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Fair Value Measurements (Schedule Of Carrying Values And Estimated Fair Values Of Debt Instruments) (Details) (USD $)
In Millions, unless otherwise specified
Mar. 31, 2013
Dec. 31, 2012
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Carrying Value $ 4,830.8 $ 4,845.9
Estimated Fair Value 5,341.0 5,397.7
4.70% Senior notes due 2021 [Member]
   
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Carrying Value 1,475.3 1,474.7
Estimated Fair Value 1,679.6 1,715.6
Debt instrument, interest rate, stated percentage 4.70% 4.70%
6.875% Senior notes due 2020 [Member]
   
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Carrying Value 1,036.9 1,040.6
Estimated Fair Value 1,123.5 1,138.3
Debt instrument, interest rate, stated percentage 6.875% 6.875%
3.25% Senior notes due 2016 [Member]
   
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Carrying Value 995.3 995.1
Estimated Fair Value 1,066.1 1,068.9
Debt instrument, interest rate, stated percentage 3.25% 3.25%
8.50% Senior notes due 2019 [Member]
   
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Carrying Value 612.5 616.4
Estimated Fair Value 661.9 661.7
Debt instrument, interest rate, stated percentage 8.50% 8.50%
7.875% Senior notes due 2040 [Member]
   
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Carrying Value 383.5 383.8
Estimated Fair Value 433.3 423.9
Debt instrument, interest rate, stated percentage 7.875% 7.875%
7.20% Debentures due 2027 [Member]
   
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Carrying Value 149.0 149.0
Estimated Fair Value 189.3 193.2
Debt instrument, interest rate, stated percentage 7.20% 7.20%
4.33% MARAD bonds, including current maturities, due 2016 [Member]
   
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Carrying Value 104.3 112.3
Estimated Fair Value 105.0 113.0
Debt instrument, interest rate, stated percentage 4.33% 4.33%
6.36% MARAD bonds, including current maturities, due 2015 [Member]
   
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Carrying Value 38.0 38.0
Estimated Fair Value 41.2 41.7
Debt instrument, interest rate, stated percentage 6.36% 6.36%
4.65% MARAD bonds, including current maturities, due 2020 [Member]
   
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Carrying Value 36.0 36.0
Estimated Fair Value $ 41.1 $ 41.4
Debt instrument, interest rate, stated percentage 4.65% 4.65%