Fair Value Measurements Fair Value of Derivatives by Balance Sheet Location (Details) (USD $)	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
Derivatives Fair Value [Line Items]
Maximum maturity of outstanding cash flow hedges, in months	36 months
Gain related to ineffective portion of hedging relationships	$ 0	$ 0
Unamortized losses on senior notes	4,000,000		4,000,000
Notional Amount of Interest Rate Derivatives	0		0
Unamortized gains on senior notes	71,000,000		73,000,000
Unrealized gain on interest rate cash flow hedges, pretax, AOCI	6,000,000		7,000,000
Derivative Assets	74,000,000		87,000,000
Derivative Liabilities	79,000,000		131,000,000
Designated as Hedging Instrument [Member]
Derivatives Fair Value [Line Items]
Derivative Instruments in Hedges, Assets, at Fair Value	45,000,000		51,000,000
Derivative Instruments in Hedges, Liabilities, at Fair Value	61,000,000		118,000,000
Designated as Hedging Instrument [Member] | Prepaid And Other Current Assets [Member]
Derivatives Fair Value [Line Items]
Derivative Instruments in Hedges, Assets, at Fair Value	18,000,000		31,000,000
Designated as Hedging Instrument [Member] | Other Long Term Assets [Member]
Derivatives Fair Value [Line Items]
Derivative Instruments in Hedges, Assets, at Fair Value	27,000,000		20,000,000
Designated as Hedging Instrument [Member] | Other current liabilities [Member]
Derivatives Fair Value [Line Items]
Derivative Instruments in Hedges, Liabilities, at Fair Value	41,000,000		69,000,000
Designated as Hedging Instrument [Member] | Other Long Term Liabilities [Member]
Derivatives Fair Value [Line Items]
Derivative Instruments in Hedges, Liabilities, at Fair Value	20,000,000		49,000,000
Not Designated as Hedging Instrument [Member] | Prepaid And Other Current Assets [Member]
Derivatives Fair Value [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	29,000,000		36,000,000
Not Designated as Hedging Instrument [Member] | Other current liabilities [Member]
Derivatives Fair Value [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	$ 18,000,000		$ 13,000,000