Annual report pursuant to Section 13 and 15(d)

Fair Value Of Financial Instruments (Fair Value, Assets And Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation) (Details)

v2.4.0.6
Fair Value Of Financial Instruments (Fair Value, Assets And Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation) (Details) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Derivative Financial Instruments, Assets [Member]
    
Beginning balance - January 1 $ 45.6 $ 63.2
Total gains (losses)    
Included in earnings 403.0 851.7
Settlements (319.7) (707.5)
Transfers into Level 3 49.0  
Transfers out of Level 3 (20.0) (161.8)
Ending balance - December 31 157.9 45.6
Total gains (losses) for the period included in earnings attributable to the change in unrealized gains or losses on assets and liabilities still held at the reporting date 403.0 120.2
Derivative Financial Instruments, Liabilities [Member]
    
Total gains (losses)    
Included in earnings (19.5)  
Ending balance - December 31 (19.5)  
Total gains (losses) for the period included in earnings attributable to the change in unrealized gains or losses on assets and liabilities still held at the reporting date $ 19.5