Quarterly report pursuant to Section 13 or 15(d)

FAIR VALUE MEASUREMENTS - Carrying Value And Fair Value Of Financial Instruments Disclosure (Details)

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FAIR VALUE MEASUREMENTS - Carrying Value And Fair Value Of Financial Instruments Disclosure (Details) - USD ($)
$ in Millions
Mar. 31, 2021
Dec. 31, 2020
Carrying Value    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Total long-term debt $ 5,734 $ 5,424
Fair Value    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Total long-term debt 6,451 6,065
Senior Notes | Carrying Value | Level 1    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Total long-term debt 3,957 3,802
Senior Notes | Fair Value | Level 1    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Total long-term debt 4,674 4,446
Industrial Revenue Bonds | Carrying Value | Level 1    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Total long-term debt 94 94
Industrial Revenue Bonds | Fair Value | Level 1    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Total long-term debt 94 91
Line of Credit | Carrying Value | Level 2 | ABC Facility    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Total long-term debt 1,630 1,510
Line of Credit | Carrying Value | Level 2 | EDC Revolving Facilities - outstanding balance    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Total long-term debt 53 18
Line of Credit | Fair Value | Level 2 | ABC Facility    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Total long-term debt 1,630 1,510
Line of Credit | Fair Value | Level 2 | EDC Revolving Facilities - outstanding balance    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Total long-term debt $ 53 $ 18