Valuation of Investments and Financial Instrument Assets Liabilities By Pricing Levels (Details) (USD $)
In Millions | Sep. 30, 2011 | Dec. 31, 2010 |
|---|
| Fair Value Assets And Liabilities Measured On Recurring Or Nonrecurring Basis Disclosure Items [Line Items] | | |
| Equity securities | $ 8 | $ 7 |
| Auction rate securities | 32 | 30 |
| Total | 270 | 174 |
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] | | |
| Equity securities | 8 | 7 |
| Auction rate securities | 0 | 0 |
| Total | 8 | 7 |
Quoted Prices In Active Markets for Identical Assets or Liabilities (Level 1) [Member] | Oil and gas derivative swap contracts [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] | 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] | | |
| Fair Value Assets And Liabilities Measured On Recurring Or Nonrecurring Basis Disclosure Items [Line Items] | | |
| Equity securities | 0 | 0 |
| Auction rate securities | 0 | 0 |
| Total | 61 | 89 |
Significant Other Observable Inputs (Level 2) [Member] | Oil and gas derivative swap contracts [Member] | | |
| Fair Value Assets And Liabilities Measured On Recurring Or Nonrecurring Basis Disclosure Items [Line Items] | | |
| Oil and gas derivative contracts | 61 | 89 |
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 Unobservable Inputs (Level 3) [Member] | | |
| Fair Value Assets And Liabilities Measured On Recurring Or Nonrecurring Basis Disclosure Items [Line Items] | | |
| Equity securities | 0 | 0 |
| Auction rate securities | 32 | 30 |
| Total | 201 | 78 |
Significant Unobservable Inputs (Level 3) [Member] | Oil and gas derivative swap contracts [Member] | | |
| Fair Value Assets And Liabilities Measured On Recurring Or Nonrecurring Basis Disclosure Items [Line Items] | | |
| Oil and gas derivative contracts | (12) | (11) |
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 | 181 | 59 |
Oil and gas derivative swap contracts [Member] | | |
| Fair Value Assets And Liabilities Measured On Recurring Or Nonrecurring Basis Disclosure Items [Line Items] | | |
| Oil and gas derivative contracts | 49 | 78 |
Commodity Option [Member] | | |
| Fair Value Assets And Liabilities Measured On Recurring Or Nonrecurring Basis Disclosure Items [Line Items] | | |
| Oil and gas derivative contracts | $ 181 | $ 59 |