Fair Value Measurements (Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) (USD $)	Dec. 31, 2011		Dec. 31, 2010
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money Market Funds	$ 340,000,000	[1]	$ 414,000,000	[1]
Net derivative contracts	(57,000,000)		125,000,000
Available for sale investments	15,000,000		25,000,000
Carrying (Reported) Amount, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money Market Funds	340,000,000		414,000,000
Net derivative contracts
Available for sale investments	21,000,000		27,000,000
Quoted Prices (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money Market Funds	340,000,000	[1]	414,000,000	[1]
Net derivative contracts
Available for sale investments	15,000,000		25,000,000
Other Significant Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money Market Funds	0		0
Net derivative contracts	(57,000,000)		125,000,000
Available for sale investments

[1] Money market funds are primarily comprised of United States government obligations.