Derivative Instruments (Balance Sheet Disclosure) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 8,738	$ 7,024
Derivative Liability, Fair Value, Gross Liability	8,470	6,758
Not Designated as Hedging Instrument [Member] | Commodity contracts [Member] | Current derivative assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	1,447	1,127
Derivative Liability, Fair Value, Gross Liability	510	432
Not Designated as Hedging Instrument [Member] | Commodity contracts [Member] | Current derivative liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	4,244	3,358
Derivative Liability, Fair Value, Gross Liability	5,636	4,494
Not Designated as Hedging Instrument [Member] | Commodity contracts [Member] | Non Current Other Assets Member
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	1,631	1,290
Derivative Liability, Fair Value, Gross Liability	413	250
Not Designated as Hedging Instrument [Member] | Commodity contracts [Member] | Noncurrent derivative liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	1,416	1,222
Derivative Liability, Fair Value, Gross Liability	1,898	1,579
Not Designated as Hedging Instrument [Member] | Foreign currency swaps [Member] | Current derivative liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	0	0
Derivative Liability, Fair Value, Gross Liability	3	3
Not Designated as Hedging Instrument [Member] | Foreign currency swaps [Member] | Non Current Other Assets Member
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	0	27
Derivative Liability, Fair Value, Gross Liability	0	0
Not Designated as Hedging Instrument [Member] | Foreign currency swaps [Member] | Noncurrent derivative liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	0	0
Derivative Liability, Fair Value, Gross Liability	10	0
Derivatives designated as hedging instruments [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	43	37
Derivative Liability, Fair Value, Gross Liability	320	326
Derivatives designated as hedging instruments [Member] | Interest Rate Contract [Member] | Current derivative assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	34	22
Derivative Liability, Fair Value, Gross Liability	0	0
Derivatives designated as hedging instruments [Member] | Interest Rate Contract [Member] | Current derivative liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	0	0
Derivative Liability, Fair Value, Gross Liability	63	60
Derivatives designated as hedging instruments [Member] | Interest Rate Contract [Member] | Non Current Other Assets Member
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	9	15
Derivative Liability, Fair Value, Gross Liability	0	0
Derivatives designated as hedging instruments [Member] | Interest Rate Contract [Member] | Noncurrent derivative liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	0	0
Derivative Liability, Fair Value, Gross Liability	243	260
Derivatives designated as hedging instruments [Member] | Foreign currency swaps [Member] | Current derivative liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	0	0
Derivative Liability, Fair Value, Gross Liability	3	3
Derivatives designated as hedging instruments [Member] | Foreign currency swaps [Member] | Noncurrent derivative liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	0	0
Derivative Liability, Fair Value, Gross Liability	$ 11	$ 3