PENSIONS AND OTHER POSTRETIREMENT BENEFITS (Benefit Obligations, Fair Value of Plan Assets, and Net Funded Status) (Details) - USD ($)
$ in Millions |
12 Months Ended |
|
|
|
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2018 |
Jan. 01, 2018 |
Dec. 31, 2017 |
| Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |
|
|
|
|
|
|
| Fair value of plan assets — beginning of year |
$ 215.6
|
$ 202.4
|
|
|
|
|
| Employer contributions |
3.8
|
2.1
|
|
|
|
|
| Fair value of plan assets — end of year |
229.1
|
215.6
|
$ 202.4
|
|
|
|
| Funded status at December 31: |
|
|
|
|
|
|
| Defined Benefit Plan, Plan Assets, Amount |
215.6
|
202.4
|
202.4
|
$ 229.1
|
|
$ 215.6
|
| Amounts recognized in Statements of Financial Position: |
|
|
|
|
|
|
| TOTAL POSTEMPLOYMENT BENEFIT LIABILITIES |
|
|
|
(248.7)
|
$ (257.7)
|
(257.7)
|
| Pension Benefits [Member] |
|
|
|
|
|
|
| Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |
|
|
|
|
|
|
| Benefit obligations — beginning of year |
(973.1)
|
(931.6)
|
|
|
|
|
| Service cost (excluding expenses) |
18.7
|
17.1
|
17.6
|
|
|
|
| Interest cost |
30.3
|
30.5
|
30.3
|
|
|
|
| Plan amendments |
2.2
|
0.0
|
|
|
|
|
| Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Curtailment |
(0.9)
|
0.0
|
|
|
|
|
| Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss) |
(57.0)
|
54.6
|
|
|
|
|
| Defined Benefit Plan, Benefit Obligation, Benefits Paid |
60.7
|
60.7
|
|
|
|
|
| Participant contributions |
0.0
|
0.0
|
|
|
|
|
| Federal subsidy on benefits paid |
0.0
|
0.0
|
|
|
|
|
| Benefit obligations — end of year |
(905.7)
|
(973.1)
|
(931.6)
|
|
|
|
| Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |
|
|
|
|
|
|
| Fair value of plan assets — beginning of year |
749.8
|
685.8
|
|
|
|
|
| Actual return on plan assets |
(29.6)
|
100.2
|
|
|
|
|
| Participant contributions |
0.0
|
0.0
|
|
|
|
|
| Employer contributions |
27.6
|
24.4
|
|
|
|
|
| Assets Transferred to (from) Plan |
0.1
|
0.1
|
|
|
|
|
| Benefits paid |
(60.7)
|
(60.7)
|
|
|
|
|
| Fair value of plan assets — end of year |
687.2
|
749.8
|
685.8
|
|
|
|
| Funded status at December 31: |
|
|
|
|
|
|
| Defined Benefit Plan, Plan Assets, Amount |
749.8
|
685.8
|
685.8
|
687.2
|
|
749.8
|
| Defined Benefit Plan, Benefit Obligation |
(973.1)
|
(931.6)
|
(931.6)
|
(905.7)
|
|
(973.1)
|
| Defined Benefit Plan, Funded (Unfunded) Status of Plan |
|
|
|
(218.5)
|
|
(223.3)
|
| Total amount recognized |
|
|
|
(218.5)
|
|
(223.3)
|
| Amounts recognized in Statements of Financial Position: |
|
|
|
|
|
|
| Assets, Noncurrent |
|
|
|
0.0
|
|
0.0
|
| Current liabilities |
|
|
|
(0.1)
|
|
(0.5)
|
| TOTAL POSTEMPLOYMENT BENEFIT LIABILITIES |
|
|
|
(218.4)
|
|
(222.8)
|
| Total amount recognized |
|
|
|
(218.5)
|
|
(223.3)
|
| Amounts recognized in accumulated other comprehensive income: |
|
|
|
|
|
|
| Prior service cost |
|
|
|
8.5
|
|
8.8
|
| Net actuarial loss |
|
|
|
330.1
|
|
318.7
|
| Net amount recognized |
|
|
|
338.6
|
|
327.5
|
| Other Benefits [Member] |
|
|
|
|
|
|
| Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |
|
|
|
|
|
|
| Benefit obligations — beginning of year |
(265.9)
|
(264.6)
|
|
|
|
|
| Service cost (excluding expenses) |
2.2
|
1.8
|
1.7
|
|
|
|
| Interest cost |
8.3
|
8.3
|
9.1
|
|
|
|
| Plan amendments |
12.8
|
0.0
|
|
|
|
|
| Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Curtailment |
0.0
|
0.0
|
|
|
|
|
| Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss) |
(29.4)
|
7.4
|
|
|
|
|
| Defined Benefit Plan, Benefit Obligation, Benefits Paid |
24.4
|
21.4
|
|
|
|
|
| Participant contributions |
5.6
|
4.6
|
|
|
|
|
| Federal subsidy on benefits paid |
0.9
|
0.6
|
|
|
|
|
| Benefit obligations — end of year |
(241.9)
|
(265.9)
|
(264.6)
|
|
|
|
| Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |
|
|
|
|
|
|
| Fair value of plan assets — beginning of year |
262.5
|
253.0
|
|
|
|
|
| Actual return on plan assets |
(8.2)
|
24.2
|
|
|
|
|
| Participant contributions |
0.5
|
0.3
|
|
|
|
|
| Employer contributions |
3.0
|
1.7
|
|
|
|
|
| Assets Transferred to (from) Plan |
0.0
|
0.0
|
|
|
|
|
| Benefits paid |
(17.6)
|
(16.7)
|
|
|
|
|
| Fair value of plan assets — end of year |
240.2
|
262.5
|
253.0
|
|
|
|
| Funded status at December 31: |
|
|
|
|
|
|
| Defined Benefit Plan, Plan Assets, Amount |
262.5
|
253.0
|
253.0
|
240.2
|
|
262.5
|
| Defined Benefit Plan, Benefit Obligation |
(265.9)
|
(264.6)
|
$ (264.6)
|
(241.9)
|
|
(265.9)
|
| Defined Benefit Plan, Funded (Unfunded) Status of Plan |
|
|
|
(1.7)
|
|
(3.4)
|
| Total amount recognized |
|
|
|
(1.7)
|
|
(3.4)
|
| Amounts recognized in Statements of Financial Position: |
|
|
|
|
|
|
| Assets, Noncurrent |
|
|
|
32.1
|
|
35.4
|
| Current liabilities |
|
|
|
(3.5)
|
|
(3.9)
|
| TOTAL POSTEMPLOYMENT BENEFIT LIABILITIES |
|
|
|
(30.3)
|
|
(34.9)
|
| Total amount recognized |
|
|
|
(1.7)
|
|
(3.4)
|
| Amounts recognized in accumulated other comprehensive income: |
|
|
|
|
|
|
| Prior service cost |
|
|
|
(9.9)
|
|
(25.6)
|
| Net actuarial loss |
|
|
|
82.1
|
|
88.3
|
| Net amount recognized |
|
|
|
72.2
|
|
62.7
|
| Salaried Employees [Member] | Pension Benefits [Member] |
|
|
|
|
|
|
| Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |
|
|
|
|
|
|
| Benefit obligations — beginning of year |
(368.0)
|
|
|
|
|
|
| Benefit obligations — end of year |
(340.8)
|
(368.0)
|
|
|
|
|
| Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |
|
|
|
|
|
|
| Fair value of plan assets — beginning of year |
269.4
|
|
|
|
|
|
| Fair value of plan assets — end of year |
249.8
|
269.4
|
|
|
|
|
| Funded status at December 31: |
|
|
|
|
|
|
| Defined Benefit Plan, Plan Assets, Amount |
269.4
|
269.4
|
|
249.8
|
|
269.4
|
| Defined Benefit Plan, Benefit Obligation |
(368.0)
|
(368.0)
|
|
(340.8)
|
|
(368.0)
|
| Defined Benefit Plan, Funded (Unfunded) Status of Plan |
|
|
|
(91.0)
|
|
(98.6)
|
| Salaried Employees [Member] | Other Benefits [Member] |
|
|
|
|
|
|
| Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |
|
|
|
|
|
|
| Benefit obligations — beginning of year |
(37.7)
|
|
|
|
|
|
| Benefit obligations — end of year |
(32.9)
|
(37.7)
|
|
|
|
|
| Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |
|
|
|
|
|
|
| Fair value of plan assets — beginning of year |
0.0
|
|
|
|
|
|
| Fair value of plan assets — end of year |
0.0
|
0.0
|
|
|
|
|
| Funded status at December 31: |
|
|
|
|
|
|
| Defined Benefit Plan, Plan Assets, Amount |
0.0
|
0.0
|
|
0.0
|
|
0.0
|
| Defined Benefit Plan, Benefit Obligation |
(37.7)
|
(37.7)
|
|
(32.9)
|
|
(37.7)
|
| Defined Benefit Plan, Funded (Unfunded) Status of Plan |
|
|
|
(32.9)
|
|
(37.7)
|
| Hourly Employees [Member] | Pension Benefits [Member] |
|
|
|
|
|
|
| Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |
|
|
|
|
|
|
| Benefit obligations — beginning of year |
(590.0)
|
|
|
|
|
|
| Benefit obligations — end of year |
(548.9)
|
(590.0)
|
|
|
|
|
| Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |
|
|
|
|
|
|
| Fair value of plan assets — beginning of year |
473.0
|
|
|
|
|
|
| Fair value of plan assets — end of year |
429.4
|
473.0
|
|
|
|
|
| Funded status at December 31: |
|
|
|
|
|
|
| Defined Benefit Plan, Plan Assets, Amount |
473.0
|
473.0
|
|
429.4
|
|
473.0
|
| Defined Benefit Plan, Benefit Obligation |
(590.0)
|
(590.0)
|
|
(548.9)
|
|
(590.0)
|
| Defined Benefit Plan, Funded (Unfunded) Status of Plan |
|
|
|
(119.5)
|
|
(117.0)
|
| Hourly Employees [Member] | Other Benefits [Member] |
|
|
|
|
|
|
| Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |
|
|
|
|
|
|
| Benefit obligations — beginning of year |
(228.2)
|
|
|
|
|
|
| Benefit obligations — end of year |
(209.0)
|
(228.2)
|
|
|
|
|
| Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |
|
|
|
|
|
|
| Fair value of plan assets — beginning of year |
262.5
|
|
|
|
|
|
| Fair value of plan assets — end of year |
240.2
|
262.5
|
|
|
|
|
| Funded status at December 31: |
|
|
|
|
|
|
| Defined Benefit Plan, Plan Assets, Amount |
262.5
|
262.5
|
|
240.2
|
|
262.5
|
| Defined Benefit Plan, Benefit Obligation |
(228.2)
|
(228.2)
|
|
(209.0)
|
|
(228.2)
|
| Defined Benefit Plan, Funded (Unfunded) Status of Plan |
|
|
|
31.2
|
|
34.3
|
| Mining Employees [Member] | Pension Benefits [Member] |
|
|
|
|
|
|
| Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |
|
|
|
|
|
|
| Benefit obligations — beginning of year |
(10.3)
|
|
|
|
|
|
| Benefit obligations — end of year |
(10.7)
|
(10.3)
|
|
|
|
|
| Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |
|
|
|
|
|
|
| Fair value of plan assets — beginning of year |
7.4
|
|
|
|
|
|
| Fair value of plan assets — end of year |
8.0
|
7.4
|
|
|
|
|
| Funded status at December 31: |
|
|
|
|
|
|
| Defined Benefit Plan, Plan Assets, Amount |
7.4
|
7.4
|
|
8.0
|
|
7.4
|
| Defined Benefit Plan, Benefit Obligation |
(10.3)
|
(10.3)
|
|
(10.7)
|
|
(10.3)
|
| Defined Benefit Plan, Funded (Unfunded) Status of Plan |
|
|
|
(2.7)
|
|
(2.9)
|
| Supplemental Executive Retirement Plan S E R P [Member] | Pension Benefits [Member] |
|
|
|
|
|
|
| Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |
|
|
|
|
|
|
| Benefit obligations — beginning of year |
(4.8)
|
|
|
|
|
|
| Benefit obligations — end of year |
(5.3)
|
(4.8)
|
|
|
|
|
| Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |
|
|
|
|
|
|
| Fair value of plan assets — beginning of year |
0.0
|
|
|
|
|
|
| Fair value of plan assets — end of year |
0.0
|
0.0
|
|
|
|
|
| Funded status at December 31: |
|
|
|
|
|
|
| Defined Benefit Plan, Plan Assets, Amount |
0.0
|
0.0
|
|
0.0
|
|
0.0
|
| Defined Benefit Plan, Benefit Obligation |
$ (4.8)
|
$ (4.8)
|
|
(5.3)
|
|
(4.8)
|
| Defined Benefit Plan, Funded (Unfunded) Status of Plan |
|
|
|
$ (5.3)
|
|
$ (4.8)
|