Fair Value Measurements (Details) (USD $)	Jun. 30, 2014		Dec. 31, 2013
Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term Debt, Fair Value	$ 2,900,000,000		$ 2,600,000,000
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds (1)	90,000,000	[1]	465,000,000	[1]
Net derivative contracts	26,000,000		(25,000,000)
Available for sale investments	37,000,000		18,000,000
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Level 3 Assets and Liabilities	0		0
Fair Value, Measurements, Recurring | Total Cost Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds (1)	90,000,000	[1]	465,000,000	[1]
Net derivative contracts	0		0
Available for sale investments	20,000,000		8,000,000
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds (1)	90,000,000	[1]	465,000,000	[1]
Net derivative contracts	0		0
Available for sale investments	37,000,000		18,000,000
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds (1)	0	[1]	0	[1]
Net derivative contracts	26,000,000		(25,000,000)
Available for sale investments	$ 0		$ 0

[1] Money market funds are comprised primarily of government obligations and other first tier obligations.