Income Taxes (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Deferred income tax assets
Derivative instruments	$ 309,000,000	$ 204,000,000
Income taxes refundable through future rates	375,000,000	271,000,000
Pension and other postretirement benefits	591,000,000	447,000,000
Other	522,000,000	501,000,000
Tax credit carry forwards	872,000,000	839,000,000
Net operating loss carry forwards	291,000,000	105,000,000
Valuation allowance	(71,000,000)	(60,000,000)
Total deferred income tax assets	2,889,000,000	2,307,000,000
Deferred income tax liabilities
Accumulated depreciation and property cost differences	(3,098,000,000)	(2,439,000,000)
Income taxes recoverable through future rates	(1,271,000,000)	(875,000,000)
Other	(303,000,000)	(386,000,000)
Total deferred income tax liabilities	(4,672,000,000)	(3,700,000,000)
Total net deferred income tax liabilities	(1,783,000,000)	(1,393,000,000)
Net deferred income tax classification
Current deferred income tax assets, included in deferred tax assets	371,000,000	156,000,000
Noncurrent deferred income tax assets, included in other assets and deferred debits	27,000,000	34,000,000
Noncurrent deferred income tax liabilities, included in noncurrent income tax liabilities	(2,181,000,000)	(1,583,000,000)
Total net deferred income tax liabilities	(1,783,000,000)	(1,393,000,000)
Alternative minimum tax credits included in tax credit carry forwards	868,000,000
Federal general business credits included in tax credit carry forwards	4,000,000
Federal GBC income tax credits included in tax credit carry forwards, expiration dates	2028 through 2031
Gross federal net operating loss carry forwards, amount	623,000,000
Gross federal net operating loss carry forwards, expiration dates	2031
Amount of gross federal net operating loss attributable to excess tax deductions attributable to stock based compensation	14,000,000
Gross state net operating loss carry forwards, amount	1,900,000,000
Gross state net operating loss carry forwards, expiration dates	2012 through 2031
Valuation allowances, increase in current year	11,000,000
Reconciliations of effective income tax rate to the statutory federal income tax rate
Effective income tax rate	35.60%	38.30%	32.10%
State income taxes, net of federal benefit	(4.30%)	(4.30%)	(3.70%)
Investment tax credit amortization	0.80%	0.50%	0.80%
Employee stock ownership plan dividends	1.40%	0.90%	1.00%
Domestic manufacturing deduction	0.00%	0.00%	0.80%
AFUDC equity	2.60%	1.40%	2.20%
Other differences, net	(1.10%)	(1.80%)	1.80%
Statutory federal income tax rate	35.00%	35.00%	35.00%
Income tax expense applicable to continuing operations composition
Current - federal	(91,000,000)	(46,000,000)	227,000,000
Current - state	29,000,000	(13,000,000)	41,000,000
Total current income tax expense (benefit)	(62,000,000)	(59,000,000)	268,000,000
Deferred - federal	578,000,000	542,000,000	114,000,000
Deferred - state	27,000,000	100,000,000	25,000,000
Total deferred income tax expense (benefit)	605,000,000	642,000,000	139,000,000
Investment tax credit	(7,000,000)	(7,000,000)	(10,000,000)
Net operating loss carry forward	(213,000,000)	(37,000,000)	0
Beginning-of-the-year valuation allowance change	0	0	0
Total income tax expense	323,000,000	539,000,000	397,000,000
Changes to unrecognized tax benefits
Amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate for income from continuing operations	6,000,000	8,000,000	9,000,000
Unrecognized tax benefits at beginning of period	176,000,000	160,000,000	104,000,000
Gross amounts of increases as a result of tax positions taken in a prior period	88,000,000	10,000,000	11,000,000
Gross amounts of decreases as a result of tax positions taken in a prior period	(24,000,000)	(4,000,000)	(3,000,000)
Gross amounts of increases as a result of tax positions taken in the current period	9,000,000	14,000,000	52,000,000
Gross amounts of decreases as a result of tax positions taken in the current period	(8,000,000)	(4,000,000)	(4,000,000)
Amount of net increases (decreases) relating to settlements with taxing authorities	(68,000,000)	0	0
Unrecognized tax benefits at end of period	173,000,000	176,000,000	160,000,000
Open tax years by jurisdiction	Our federal tax years are open for examination from 2007 forward, and our open state tax years in our major jurisdictions generally are from 2003 forward.
Significant change in unrecognized tax benefits is reasonably possible	25,000,000
Net interest expense related to unrecognized tax benefits	(24,000,000)	9,000,000	9,000,000
Net interest expense related to unrecognized tax benefits, deferred as a regulatory asset	(22,000,000)	5,000,000	5,000,000
Interest and penalties accrued	$ 21,000,000	$ 45,000,000	$ 36,000,000