Fair Value (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Assets [Abstract]
Nuclear decommissioning trusts	$ 937	$ 939
Other investments	111	111
Derivative assets Abstract [Abstract]
Derivative Asset, Fair Value, Gross Asset	2,805	2,848
Derivative Assets	1,344	1,258
Liabilities [Abstract]
Derivative Liability, Fair Value, Gross Liability	(2,811)	(2,936)
Derivative Liabilities	(247)	(252)
Derivative Assets (Liabilities), at Fair Value, Net	1,097	1,006
Derivative Assets, Current	222	131
Derivative Assets, Noncurrent	74	77
Derivative Liabilities, Current	158	142
Derivative Liabilities, Noncurrent	89	110
Current Asset [Member]
Liabilities [Abstract]
Derivative Assets, Current	222	131
Non Current Asset [Member]
Liabilities [Abstract]
Derivative Assets, Noncurrent	1,122	1,127
Current Liability [Member]
Liabilities [Abstract]
Derivative Liabilities, Current	(158)	(142)
Noncurrent Liability [Member]
Liabilities [Abstract]
Derivative Liabilities, Noncurrent	(89)	(110)
Foreign currency exchange contracts [Member]
Derivative assets Abstract [Abstract]
Derivative Asset, Fair Value, Gross Asset	0	0
Liabilities [Abstract]
Derivative Liability, Fair Value, Gross Liability	(2)	(10)
Interest rate contracts [Member]
Liabilities [Abstract]
Derivative Liability, Fair Value, Gross Liability	(1)	(1)
Natural Gas [Member]
Derivative assets Abstract [Abstract]
Derivative Asset, Fair Value, Gross Asset	33	26
Liabilities [Abstract]
Derivative Liability, Fair Value, Gross Liability	(104)	(163)
Electricity [Member]
Derivative assets Abstract [Abstract]
Derivative Asset, Fair Value, Gross Asset	257	177
Liabilities [Abstract]
Derivative Liability, Fair Value, Gross Liability	(140)	(73)
Other [Member]
Derivative assets Abstract [Abstract]
Derivative Asset, Fair Value, Gross Asset	6	5
Liabilities [Abstract]
Derivative Liability, Fair Value, Gross Liability	0	(5)
Total derivative assets [Member]
Derivative assets Abstract [Abstract]
Derivative Assets	296	208
Total derivative liabilities [Member]
Liabilities [Abstract]
Derivative Liabilities	(247)	(252)
Fair Value, Inputs, Level 1 [Member]
Assets [Abstract]
Nuclear decommissioning trusts	577	599
Other investments	57	56
Derivative assets Abstract [Abstract]
Derivative Assets	2,583	2,569
Liabilities [Abstract]
Derivative Liabilities	(1,959)	(1,907)
Derivative Assets (Liabilities), at Fair Value, Net	624	662
Derivative Assets, Current	1,571	1,299
Derivative Assets, Noncurrent	1,012	1,270
Derivative Liabilities, Current	(1,603)	(1,290)
Derivative Liabilities, Noncurrent	(356)	(617)
Fair Value, Inputs, Level 1 [Member] | Foreign currency exchange contracts [Member]
Derivative assets Abstract [Abstract]
Derivative Asset, Fair Value, Gross Asset	0	0
Liabilities [Abstract]
Derivative Liability, Fair Value, Gross Liability	0	0
Fair Value, Inputs, Level 1 [Member] | Interest rate contracts [Member]
Liabilities [Abstract]
Derivative Liability, Fair Value, Gross Liability	0	0
Fair Value, Inputs, Level 1 [Member] | Natural Gas [Member]
Derivative assets Abstract [Abstract]
Derivative Asset, Fair Value, Gross Asset	1,926	1,846
Liabilities [Abstract]
Derivative Liability, Fair Value, Gross Liability	(1,940)	(1,844)
Fair Value, Inputs, Level 1 [Member] | Electricity [Member]
Derivative assets Abstract [Abstract]
Derivative Asset, Fair Value, Gross Asset	0	0
Liabilities [Abstract]
Derivative Liability, Fair Value, Gross Liability	0	0
Fair Value, Inputs, Level 1 [Member] | Other [Member]
Derivative assets Abstract [Abstract]
Derivative Asset, Fair Value, Gross Asset	23	68
Liabilities [Abstract]
Derivative Liability, Fair Value, Gross Liability	(19)	(63)
Fair Value, Inputs, Level 1 [Member] | Total derivative assets [Member]
Derivative assets Abstract [Abstract]
Derivative Assets	1,949	1,914
Fair Value, Inputs, Level 1 [Member] | Total derivative liabilities [Member]
Liabilities [Abstract]
Derivative Liabilities	(1,959)	(1,907)
Fair Value, Inputs, Level 2 [Member]
Assets [Abstract]
Nuclear decommissioning trusts	360	340
Other investments	54	55
Derivative assets Abstract [Abstract]
Derivative Assets	1,020	1,196
Liabilities [Abstract]
Derivative Liabilities	(646)	(955)
Derivative Assets (Liabilities), at Fair Value, Net	374	241
Derivative Assets, Current	520	663
Derivative Assets, Noncurrent	500	533
Derivative Liabilities, Current	(527)	(730)
Derivative Liabilities, Noncurrent	(119)	(225)
Fair Value, Inputs, Level 2 [Member] | Foreign currency exchange contracts [Member]
Derivative assets Abstract [Abstract]
Derivative Asset, Fair Value, Gross Asset	3	20
Liabilities [Abstract]
Derivative Liability, Fair Value, Gross Liability	(5)	(30)
Fair Value, Inputs, Level 2 [Member] | Interest rate contracts [Member]
Liabilities [Abstract]
Derivative Liability, Fair Value, Gross Liability	(1)	(1)
Fair Value, Inputs, Level 2 [Member] | Natural Gas [Member]
Derivative assets Abstract [Abstract]
Derivative Asset, Fair Value, Gross Asset	78	128
Liabilities [Abstract]
Derivative Liability, Fair Value, Gross Liability	(126)	(263)
Fair Value, Inputs, Level 2 [Member] | Electricity [Member]
Derivative assets Abstract [Abstract]
Derivative Asset, Fair Value, Gross Asset	523	649
Liabilities [Abstract]
Derivative Liability, Fair Value, Gross Liability	(513)	(653)
Fair Value, Inputs, Level 2 [Member] | Other [Member]
Derivative assets Abstract [Abstract]
Derivative Asset, Fair Value, Gross Asset	2	4
Liabilities [Abstract]
Derivative Liability, Fair Value, Gross Liability	(1)	(8)
Fair Value, Inputs, Level 2 [Member] | Total derivative assets [Member]
Derivative assets Abstract [Abstract]
Derivative Assets	606	801
Fair Value, Inputs, Level 2 [Member] | Total derivative liabilities [Member]
Liabilities [Abstract]
Derivative Liabilities	(646)	(955)
Fair Value, Inputs, Level 3 [Member]
Assets [Abstract]
Nuclear decommissioning trusts	0	0
Other investments	0	0
Derivative assets Abstract [Abstract]
Derivative Assets	250	133
Liabilities [Abstract]
Derivative Liabilities	(206)	(74)
Derivative Assets (Liabilities), at Fair Value, Net	44	59
Derivative Assets, Current	181	49
Derivative Assets, Noncurrent	69	84
Derivative Liabilities, Current	(152)	(21)
Derivative Liabilities, Noncurrent	(54)	(53)
Fair Value, Inputs, Level 3 [Member] | Foreign currency exchange contracts [Member]
Derivative assets Abstract [Abstract]
Derivative Asset, Fair Value, Gross Asset	0	0
Liabilities [Abstract]
Derivative Liability, Fair Value, Gross Liability	0	0
Fair Value, Inputs, Level 3 [Member] | Interest rate contracts [Member]
Liabilities [Abstract]
Derivative Liability, Fair Value, Gross Liability	0	0
Fair Value, Inputs, Level 3 [Member] | Natural Gas [Member]
Derivative assets Abstract [Abstract]
Derivative Asset, Fair Value, Gross Asset	20	12
Liabilities [Abstract]
Derivative Liability, Fair Value, Gross Liability	(14)	(11)
Fair Value, Inputs, Level 3 [Member] | Electricity [Member]
Derivative assets Abstract [Abstract]
Derivative Asset, Fair Value, Gross Asset	224	117
Liabilities [Abstract]
Derivative Liability, Fair Value, Gross Liability	(192)	(63)
Fair Value, Inputs, Level 3 [Member] | Other [Member]
Derivative assets Abstract [Abstract]
Derivative Asset, Fair Value, Gross Asset	6	4
Liabilities [Abstract]
Derivative Liability, Fair Value, Gross Liability	0	0
Fair Value, Inputs, Level 3 [Member] | Total derivative assets [Member]
Derivative assets Abstract [Abstract]
Derivative Assets	250	133
Fair Value, Inputs, Level 3 [Member] | Total derivative liabilities [Member]
Liabilities [Abstract]
Derivative Liabilities	(206)	(74)
Netting Adjustments [Member]
Assets [Abstract]
Nuclear decommissioning trusts	0	0
Other investments	0	0
Derivative assets Abstract [Abstract]
Derivative Assets	(2,509)	(2,640)
Liabilities [Abstract]
Derivative Liabilities	2,564	2,684
Derivative Assets (Liabilities), at Fair Value, Net	55	44
Derivative Assets, Current	(2,050)	(1,880)
Derivative Assets, Noncurrent	(459)	(760)
Derivative Liabilities, Current	2,124	1,899
Derivative Liabilities, Noncurrent	440	785
Netting Adjustments [Member] | Foreign currency exchange contracts [Member]
Derivative assets Abstract [Abstract]
Derivative Asset, Fair Value, Gross Asset	(3)	(20)
Liabilities [Abstract]
Derivative Liability, Fair Value, Gross Liability	3	20
Netting Adjustments [Member] | Interest rate contracts [Member]
Liabilities [Abstract]
Derivative Liability, Fair Value, Gross Liability	0	0
Netting Adjustments [Member] | Natural Gas [Member]
Derivative assets Abstract [Abstract]
Derivative Asset, Fair Value, Gross Asset	(1,991)	(1,960)
Liabilities [Abstract]
Derivative Liability, Fair Value, Gross Liability	1,976	1,955
Netting Adjustments [Member] | Electricity [Member]
Derivative assets Abstract [Abstract]
Derivative Asset, Fair Value, Gross Asset	(490)	(589)
Liabilities [Abstract]
Derivative Liability, Fair Value, Gross Liability	565	643
Netting Adjustments [Member] | Other [Member]
Derivative assets Abstract [Abstract]
Derivative Asset, Fair Value, Gross Asset	(25)	(71)
Liabilities [Abstract]
Derivative Liability, Fair Value, Gross Liability	20	66
Netting Adjustments [Member] | Total derivative assets [Member]
Derivative assets Abstract [Abstract]
Derivative Assets	(2,509)	(2,640)
Netting Adjustments [Member] | Total derivative liabilities [Member]
Liabilities [Abstract]
Derivative Liabilities	$ 2,564	$ 2,684