Valuation of Investments and Financial Instrument Assets Liabilities By Pricing Levels (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Fair Value Assets And Liabilities Measured On Recurring Or Nonrecurring Basis Disclosure Items [Line Items]
Money market fund investments	$ 430
Equity securities	11	10
Auction rate securities	34	32
Total	685	179
Commodity Option [Member]
Fair Value Assets And Liabilities Measured On Recurring Or Nonrecurring Basis Disclosure Items [Line Items]
Oil and gas derivative contracts	191	81
Oil and gas derivative swap and basis contracts [Member]
Fair Value Assets And Liabilities Measured On Recurring Or Nonrecurring Basis Disclosure Items [Line Items]
Oil and gas derivative contracts	19	56
Quoted Prices In Active Markets for Identical Assets or Liabilities (Level 1) [Member]
Fair Value Assets And Liabilities Measured On Recurring Or Nonrecurring Basis Disclosure Items [Line Items]
Money market fund investments	430
Equity securities	11	10
Auction rate securities	0	0
Total	441	10
Quoted Prices In Active Markets for Identical Assets or Liabilities (Level 1) [Member] | Commodity Option [Member]
Fair Value Assets And Liabilities Measured On Recurring Or Nonrecurring Basis Disclosure Items [Line Items]
Oil and gas derivative contracts	0	0
Quoted Prices In Active Markets for Identical Assets or Liabilities (Level 1) [Member] | Oil and gas derivative swap and basis contracts [Member]
Fair Value Assets And Liabilities Measured On Recurring Or Nonrecurring Basis Disclosure Items [Line Items]
Oil and gas derivative contracts	0	0
Significant Other Observable Inputs (Level 2) [Member]
Fair Value Assets And Liabilities Measured On Recurring Or Nonrecurring Basis Disclosure Items [Line Items]
Money market fund investments	0
Equity securities	0	0
Auction rate securities	0	0
Total	25	66
Significant Other Observable Inputs (Level 2) [Member] | Commodity Option [Member]
Fair Value Assets And Liabilities Measured On Recurring Or Nonrecurring Basis Disclosure Items [Line Items]
Oil and gas derivative contracts	0	0
Significant Other Observable Inputs (Level 2) [Member] | Oil and gas derivative swap and basis contracts [Member]
Fair Value Assets And Liabilities Measured On Recurring Or Nonrecurring Basis Disclosure Items [Line Items]
Oil and gas derivative contracts	25	66
Significant Unobservable Inputs (Level 3) [Member]
Fair Value Assets And Liabilities Measured On Recurring Or Nonrecurring Basis Disclosure Items [Line Items]
Money market fund investments	0
Equity securities	0	0
Auction rate securities	34	32
Total	219	103
Significant Unobservable Inputs (Level 3) [Member] | Commodity Option [Member]
Fair Value Assets And Liabilities Measured On Recurring Or Nonrecurring Basis Disclosure Items [Line Items]
Oil and gas derivative contracts	191	81
Significant Unobservable Inputs (Level 3) [Member] | Oil and gas derivative swap and basis contracts [Member]
Fair Value Assets And Liabilities Measured On Recurring Or Nonrecurring Basis Disclosure Items [Line Items]
Oil and gas derivative contracts	$ (6)	$ (10)