Accounting for Derivative Instruments and Hedging Activities (Details) (USD $)	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2012 Interest Rate Swap [Member] Designated as Hedging Instrument [Member] Other long-term liabilities [Member]	Dec. 31, 2011 Interest Rate Swap [Member] Designated as Hedging Instrument [Member] Other long-term liabilities [Member]	Mar. 31, 2012 Interest Rate Swap [Member] Designated as Hedging Instrument [Member] Accumulated other comprehensive income (loss) [Member]	Dec. 31, 2011 Interest Rate Swap [Member] Designated as Hedging Instrument [Member] Accumulated other comprehensive income (loss) [Member]	Apr. 30, 2012 Entering in interest rate swap agreements [Member]
Derivatives, Fair Value [Line Items]
Fair value of interest rate derivatives designated as hedges			$ 64,000,000	$ 65,000,000	$ (64,000,000)	$ (65,000,000)
Notional amount of interest rate derivatives	$ 2,000,000,000	$ 2,000,000,000					$ 1,100,000,000