Derivative Financial Instruments Recorded in Balance Sheet (Details) (USD $)
In Millions | Sep. 30, 2011 | Dec. 31, 2010 |
|---|
| Derivative Financial Instruments That Are Recorded In Balance Sheet [Abstract] | | |
| Total | $ 230 | $ 137 |
Basis contracts [Member] | Derivative assets - current [Member] | | |
| Derivative Financial Instruments That Are Recorded In Balance Sheet [Abstract] | | |
| Derivative Asset Not Designated As Hedging Instrument, Fair Value | (4) | (5) |
Natural gas contracts [Member] | Derivative assets - current [Member] | | |
| Derivative Financial Instruments That Are Recorded In Balance Sheet [Abstract] | | |
| Derivative Asset Not Designated As Hedging Instrument, Fair Value | 130 | 201 |
Oil contracts [Member] | Derivative assets - current [Member] | | |
| Derivative Financial Instruments That Are Recorded In Balance Sheet [Abstract] | | |
| Derivative Asset Not Designated As Hedging Instrument, Fair Value | 44 | 1 |
Basis contracts [Member] | Derivative assets - noncurrent [Member] | | |
| Derivative Financial Instruments That Are Recorded In Balance Sheet [Abstract] | | |
| Derivative Asset Not Designated As Hedging Instrument, Fair Value | (1) | (6) |
Natural gas contracts [Member] | Derivative assets - noncurrent [Member] | | |
| Derivative Financial Instruments That Are Recorded In Balance Sheet [Abstract] | | |
| Derivative Asset Not Designated As Hedging Instrument, Fair Value | 43 | 45 |
Oil contracts [Member] | Derivative assets - noncurrent [Member] | | |
| Derivative Financial Instruments That Are Recorded In Balance Sheet [Abstract] | | |
| Derivative Asset Not Designated As Hedging Instrument, Fair Value | 25 | 0 |
Derivative liabilities - current [Member] | Basis contracts [Member] | | |
| Derivative Financial Instruments That Are Recorded In Balance Sheet [Abstract] | | |
| Derivative Liability Not Designated as Hedging Instrument Fair Value | (6) | 0 |
Derivative liabilities - current [Member] | Oil contracts [Member] | | |
| Derivative Financial Instruments That Are Recorded In Balance Sheet [Abstract] | | |
| Derivative Liability Not Designated as Hedging Instrument Fair Value | 0 | (53) |
Basis contracts [Member] | Derivative liabilities - noncurrent [Member] | | |
| Derivative Financial Instruments That Are Recorded In Balance Sheet [Abstract] | | |
| Derivative Liability Not Designated as Hedging Instrument Fair Value | (1) | 0 |
Natural gas contracts [Member] | Derivative liabilities - noncurrent [Member] | | |
| Derivative Financial Instruments That Are Recorded In Balance Sheet [Abstract] | | |
| Derivative Liability Not Designated as Hedging Instrument Fair Value | 0 | (4) |
Oil contracts [Member] | Derivative liabilities - noncurrent [Member] | | |
| Derivative Financial Instruments That Are Recorded In Balance Sheet [Abstract] | | |
| Derivative Liability Not Designated as Hedging Instrument Fair Value | $ 0 | $ (42) |