Income Taxes (Tables)

12 Months Ended

Dec. 31, 2011

Income Tax Disclosure [Abstract]

Schedule of deferred tax assets and liabilities

(in millions)			2011		2010
Deferred income tax assets
	Derivative instruments		$	309	$	204
	Income taxes refundable through future rates			375		271
	Pension and other postretirement benefits			591		447
	Other			522		501
	Tax credit carry forwards			872		839
	Net operating loss carry forwards			291		105
	Valuation allowance			(71)		(60)
		Total deferred income tax assets		2,889		2,307
Deferred income tax liabilities
	Accumulated depreciation and property cost differences			(3,098)		(2,439)
	Income taxes recoverable through future rates			(1,271)		(875)
	Other			(303)		(386)
		Total deferred income tax liabilities		(4,672)		(3,700)
		Total net deferred income tax liabilities	$	(1,783)	$	(1,393)

Schedule of balance sheet classification of deferred tax assets and liabilities

(in millions)		2011		2010
Current deferred income tax assets, included in deferred tax assets		$	371	$	156
Noncurrent deferred income tax assets, included in other assets and deferred debits			27		34
Noncurrent deferred income tax liabilities, included in noncurrent income tax liabilities			(2,181)		(1,583)
	Total net deferred income tax liabilities	$	(1,783)	$	(1,393)

Schedule of effective income tax rate reconciliation

		2011			2010		2009
Effective income tax rate			35.6	%	38.3	%	32.1	%
State income taxes, net of federal benefit			(4.3)		(4.3)		(3.7)
Investment tax credit amortization			0.8		0.5		0.8
Employee stock ownership plan dividends			1.4		0.9		1.0
Domestic manufacturing deduction			0.0		0.0		0.8
AFUDC equity			2.6		1.4		2.2
Other differences, net			(1.1)		(1.8)		1.8
	Statutory federal income tax rate		35.0	%	35.0	%	35.0	%

Schedule of components of income tax expense (benefit)

(in millions)			2011		2010		2009
Current
	Federal		$	(91)	$	(46)	$	227
	State			29		(13)		41
		Total current income tax expense (benefit)		(62)		(59)		268
Deferred
	Federal			578		542		114
	State			27		100		25
		Total deferred income tax expense		605		642		139
	Investment tax credit			(7)		(7)		(10)
	Net operating loss carry forward			(213)		(37)		0
		Total income tax expense	$	323	$	539	$	397

Changes to unrecognized tax benefits during the year

(in millions)	2011		2010		2009
Unrecognized tax benefits at beginning of period	$	176	$	160	$	104
Gross amounts of increases as a result of tax positions taken in a prior period		88		10		11
Gross amounts of decreases as a result of tax positions taken in a prior period		(24)		(4)		(3)
Gross amounts of increases as a result of tax positions taken in the current period		9		14		52
Gross amounts of decreases as a result of tax positions taken in the current period		(8)		(4)		(4)
Amounts of net decreases relating to settlements with taxing authorities		(68)		0		0
Unrecognized tax benefits at end of period	$	173	$	176	$	160