Condensed Consolidating Statements (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011	Dec. 31, 2010
Operating revenues
Operating revenues	$ 2,092	$ 2,167
Affiliate revenues	0	0
Total revenues	2,092	2,167
Operating expenses
Fuel used in electric generation	685	718
Purchased power	210	220
Operation and maintenance	529	494
Depreciation, amortization and accretion	166	154
Taxes other than on income	138	140
Other	0	(10)
Total operating expenses	1,728	1,716
Operating (loss) income	364	451
Other income (expense)
Interest income	1	1
Allowance for equity funds used during construction	24	29
Other, net	13	3
Total other income (expense), net	38	33
Interest charges
Interest charges	194	199
Allowance for borrowed funds used during construction	(9)	(9)
Total interest charges, net	185	190
(Loss) income from continuing operations before income tax and equity in earnings of consolidated subsidiaries	217	294
Income tax (benefit) expense	76	107
Income from continuing operations	141	187
Discontinued operations, net of tax	11	(2)
Net income (loss)	152	185
Net income attributable to noncontrolling interests, net of tax	(2)	(1)
Net income attributable to controlling interests	150	184
Comprehensive income
Comprehensive income	157	189
Comprehensive (income) loss attributable to noncontrolling interests, net of tax	(2)	(1)
Comprehensive income attributable to controlling interests	155	188
ASSETS
Utility plant, net	22,805		22,497
Current assets
Cash and cash equivalents	565	172
Receivables, net	758		889
Notes receivable from affiliated companies	0		0
Regulatory assets	250		275
Derivative collateral posted	166		147
Prepayments and other current assets	2,096		1,942
Total current assets	3,835		3,483
Deferred debits and other assets
Investment in consolidated subsidiaries	0		0
Regulatory assets	3,123		3,025
Goodwill	3,655		3,655
Nuclear decommissioning trust funds	1,762		1,647
Other assets and deferred debits	795		752
Total deferred debits and other assets	9,335		9,079
Total assets	35,975		35,059
Equity
Common stock equity	10,009		10,021
Noncontrolling interests	2		4
Total equity	10,011	10,050	10,025	10,027
Preferred stock of subsidiaries	93		93
Long-term debt, affiliate	273		273
Long-term debt, net	11,742		11,718
Total capitalization	22,119		22,109
Current liabilities
Current portion of long-term debt	1,375		950
Short-term debt	1,056		671
Notes payable to affiliated companies	0		0
Derivative liabilities	484		436
Other current liabilities	1,847		2,028
Total current liabilities	4,762		4,085
Deferred credits and other liabilities
Noncurrent income tax liabilities	2,637		2,355
Regulatory liabilities	2,684		2,700
Other liabilities and deferred credits	3,773		3,810
Total deferred credits and other liabilities	9,094		8,865
Total capitalization and liabilities	35,975		35,059
Condensed Consolidating Statement of Cash Flows
Net cash provided (used) by operating activities	356	446
Investing activities
Gross property additions	(562)	(501)
Nuclear fuel additions	(51)	(57)
Purchases of available-for-sale securities and other investments	(363)	(1,817)
Proceeds from available-for-sale securities and other investments	359	1,809
Other investing activities	65	46
Net cash provided (used) by investing activities	(552)	(520)
Financing activities
Issuance of common stock, net	3	8
Dividends paid on common stock	(260)	(183)
Proceeds from issuance of short-term debt with original maturities greater than 90 days	65	0
Net increase (decrease) in short-term debt	320	79
Proceeds from issuance of long-term debt, net	444	494
Retirement of long-term debt	0	(700)
Other financing activities	(41)	(63)
Net cash provided (used) by financing activities	531	(365)
Net increase (decrease) in cash and cash equivalents	335	(439)
Cash and cash equivalents at beginning of period	230	611
Cash and cash equivalents at end of period	565	172
Parent
Operating revenues
Operating revenues	0	0
Affiliate revenues	0	0
Total revenues	0	0
Operating expenses
Fuel used in electric generation	0	0
Purchased power	0	0
Operation and maintenance	1	3
Depreciation, amortization and accretion	0	0
Taxes other than on income	0	0
Other	0	0
Total operating expenses	1	3
Operating (loss) income	(1)	(3)
Other income (expense)
Interest income	1	0
Allowance for equity funds used during construction	0	0
Other, net	8	0
Total other income (expense), net	9	0
Interest charges
Interest charges	66	73
Allowance for borrowed funds used during construction	0	0
Total interest charges, net	66	73
(Loss) income from continuing operations before income tax and equity in earnings of consolidated subsidiaries	(58)	(76)
Income tax (benefit) expense	(22)	(31)
Equity in earnings of consolidated subsidiaries	186	229
Income from continuing operations	150	184
Discontinued operations, net of tax	0	0
Net income (loss)	150	184
Net income attributable to noncontrolling interests, net of tax	0	0
Net income attributable to controlling interests	150	184
Comprehensive income
Comprehensive income	155	188
Comprehensive (income) loss attributable to noncontrolling interests, net of tax	0	0
Comprehensive income attributable to controlling interests	155	188
ASSETS
Utility plant, net	0		0
Current assets
Cash and cash equivalents	511	3
Receivables, net	0		0
Notes receivable from affiliated companies	63		53
Regulatory assets	0		0
Derivative collateral posted	0		0
Prepayments and other current assets	135		128
Total current assets	709		298
Deferred debits and other assets
Investment in consolidated subsidiaries	13,968		14,043
Regulatory assets	0		0
Goodwill	0		0
Nuclear decommissioning trust funds	0		0
Other assets and deferred debits	116		140
Total deferred debits and other assets	14,084		14,183
Total assets	14,793		14,481
Equity
Common stock equity	10,009		10,021
Noncontrolling interests	0		0
Total equity	10,009		10,021
Preferred stock of subsidiaries	0		0
Long-term debt, affiliate	0		0
Long-term debt, net	3,992		3,543
Total capitalization	14,001		13,564
Current liabilities
Current portion of long-term debt	450		450
Short-term debt	255		250
Notes payable to affiliated companies	0		0
Derivative liabilities	0		38
Other current liabilities	65		161
Total current liabilities	770		899
Deferred credits and other liabilities
Noncurrent income tax liabilities	0		0
Regulatory liabilities	0		0
Other liabilities and deferred credits	22		18
Total deferred credits and other liabilities	22		18
Total capitalization and liabilities	14,793		14,481
Condensed Consolidating Statement of Cash Flows
Net cash provided (used) by operating activities	227	280
Investing activities
Gross property additions	0	0
Nuclear fuel additions	0	0
Purchases of available-for-sale securities and other investments	0	0
Proceeds from available-for-sale securities and other investments	0	0
Changes in advances to affiliated companies	(10)	(75)
Contributions to consolidated subsidiaries	0	(10)
Other investing activities	(14)	0
Net cash provided (used) by investing activities	(24)	(85)
Financing activities
Issuance of common stock, net	3	8
Dividends paid on common stock	(260)	(183)
Dividends paid to parent	0	0
Proceeds from issuance of short-term debt with original maturities greater than 90 days	0
Net increase (decrease) in short-term debt	5	79
Proceeds from issuance of long-term debt, net	444	494
Retirement of long-term debt	0	(700)
Changes in advances from affiliated companies	0	0
Contributions from parent	0	0
Other financing activities	(1)	0
Net cash provided (used) by financing activities	191	(302)
Net increase (decrease) in cash and cash equivalents	394	(107)
Cash and cash equivalents at beginning of period	117	110
Cash and cash equivalents at end of period	511	3
Subsidiary Guarantor
Operating revenues
Operating revenues	1,007	1,034
Affiliate revenues	0	0
Total revenues	1,007	1,034
Operating expenses
Fuel used in electric generation	336	355
Purchased power	145	153
Operation and maintenance	160	211
Depreciation, amortization and accretion	27	25
Taxes other than on income	82	85
Other	0	(10)
Total operating expenses	750	819
Operating (loss) income	257	215
Other income (expense)
Interest income	0	1
Allowance for equity funds used during construction	9	9
Other, net	1	5
Total other income (expense), net	10	15
Interest charges
Interest charges	73	75
Allowance for borrowed funds used during construction	(4)	(4)
Total interest charges, net	69	71
(Loss) income from continuing operations before income tax and equity in earnings of consolidated subsidiaries	198	159
Income tax (benefit) expense	73	60
Equity in earnings of consolidated subsidiaries	0	0
Income from continuing operations	125	99
Discontinued operations, net of tax	11	(1)
Net income (loss)	136	98
Net income attributable to noncontrolling interests, net of tax	(1)	(1)
Net income attributable to controlling interests	135	97
Comprehensive income
Comprehensive income	137	99
Comprehensive (income) loss attributable to noncontrolling interests, net of tax	(1)	(1)
Comprehensive income attributable to controlling interests	136	98
ASSETS
Utility plant, net	10,596		10,523
Current assets
Cash and cash equivalents	33	55
Receivables, net	346		372
Notes receivable from affiliated companies	7		0
Regulatory assets	225		244
Derivative collateral posted	136		123
Prepayments and other current assets	960		852
Total current assets	1,707		1,683
Deferred debits and other assets
Investment in consolidated subsidiaries	0		0
Regulatory assets	1,659		1,602
Goodwill	0		0
Nuclear decommissioning trust funds	599		559
Other assets and deferred debits	255		242
Total deferred debits and other assets	2,513		2,403
Total assets	14,816		14,609
Equity
Common stock equity	4,759		4,728
Noncontrolling interests	2		4
Total equity	4,761		4,732
Preferred stock of subsidiaries	34		34
Long-term debt, affiliate	309		309
Long-term debt, net	4,057		4,482
Total capitalization	9,161		9,557
Current liabilities
Current portion of long-term debt	425		0
Short-term debt	360		233
Notes payable to affiliated companies	198		238
Derivative liabilities	335		268
Other current liabilities	836		839
Total current liabilities	2,154		1,578
Deferred credits and other liabilities
Noncurrent income tax liabilities	990		837
Regulatory liabilities	967		1,071
Other liabilities and deferred credits	1,544		1,566
Total deferred credits and other liabilities	3,501		3,474
Total capitalization and liabilities	14,816		14,609
Condensed Consolidating Statement of Cash Flows
Net cash provided (used) by operating activities	166	257
Investing activities
Gross property additions	(197)	(218)
Nuclear fuel additions	(13)	(7)
Purchases of available-for-sale securities and other investments	(225)	(1,661)
Proceeds from available-for-sale securities and other investments	226	1,661
Changes in advances to affiliated companies	(7)	21
Contributions to consolidated subsidiaries	0	0
Other investing activities	15	43
Net cash provided (used) by investing activities	(201)	(161)
Financing activities
Issuance of common stock, net	0	0
Dividends paid on common stock	0	0
Dividends paid to parent	(108)	(328)
Proceeds from issuance of short-term debt with original maturities greater than 90 days	65
Net increase (decrease) in short-term debt	62	0
Proceeds from issuance of long-term debt, net	0	0
Retirement of long-term debt	0	0
Changes in advances from affiliated companies	(40)	11
Contributions from parent	0	10
Other financing activities	(3)	(4)
Net cash provided (used) by financing activities	(24)	(311)
Net increase (decrease) in cash and cash equivalents	(59)	(215)
Cash and cash equivalents at beginning of period	92	270
Cash and cash equivalents at end of period	33	55
Non-Guarantor Subsidiaries
Operating revenues
Operating revenues	1,085	1,133
Affiliate revenues	59	74
Total revenues	1,144	1,207
Operating expenses
Fuel used in electric generation	349	363
Purchased power	65	67
Operation and maintenance	422	351
Depreciation, amortization and accretion	139	129
Taxes other than on income	58	59
Other	0	0
Total operating expenses	1,033	969
Operating (loss) income	111	238
Other income (expense)
Interest income	0	0
Allowance for equity funds used during construction	15	20
Other, net	2	(2)
Total other income (expense), net	17	18
Interest charges
Interest charges	55	51
Allowance for borrowed funds used during construction	(5)	(5)
Total interest charges, net	50	46
(Loss) income from continuing operations before income tax and equity in earnings of consolidated subsidiaries	78	210
Income tax (benefit) expense	27	80
Equity in earnings of consolidated subsidiaries	0	0
Income from continuing operations	51	130
Discontinued operations, net of tax	0	(1)
Net income (loss)	51	129
Net income attributable to noncontrolling interests, net of tax	0	0
Net income attributable to controlling interests	51	129
Comprehensive income
Comprehensive income	55	132
Comprehensive (income) loss attributable to noncontrolling interests, net of tax	0	0
Comprehensive income attributable to controlling interests	55	132
ASSETS
Utility plant, net	12,124		11,887
Current assets
Cash and cash equivalents	21	114
Receivables, net	412		517
Notes receivable from affiliated companies	172		219
Regulatory assets	25		31
Derivative collateral posted	30		24
Prepayments and other current assets	1,134		1,049
Total current assets	1,794		1,861
Deferred debits and other assets
Investment in consolidated subsidiaries	0		0
Regulatory assets	1,464		1,423
Goodwill	0		0
Nuclear decommissioning trust funds	1,163		1,088
Other assets and deferred debits	869		856
Total deferred debits and other assets	3,496		3,367
Total assets	17,414		17,115
Equity
Common stock equity	5,536		5,646
Noncontrolling interests	0		0
Total equity	5,536		5,646
Preferred stock of subsidiaries	59		59
Long-term debt, affiliate	0		0
Long-term debt, net	3,693		3,693
Total capitalization	9,288		9,398
Current liabilities
Current portion of long-term debt	500		500
Short-term debt	441		188
Notes payable to affiliated companies	44		34
Derivative liabilities	149		130
Other current liabilities	1,084		1,112
Total current liabilities	2,218		1,964
Deferred credits and other liabilities
Noncurrent income tax liabilities	2,062		1,976
Regulatory liabilities	1,632		1,543
Other liabilities and deferred credits	2,214		2,234
Total deferred credits and other liabilities	5,908		5,753
Total capitalization and liabilities	17,414		17,115
Condensed Consolidating Statement of Cash Flows
Net cash provided (used) by operating activities	245	337
Investing activities
Gross property additions	(365)	(283)
Nuclear fuel additions	(38)	(50)
Purchases of available-for-sale securities and other investments	(138)	(156)
Proceeds from available-for-sale securities and other investments	133	148
Changes in advances to affiliated companies	47	42
Contributions to consolidated subsidiaries	0	0
Other investing activities	64	5
Net cash provided (used) by investing activities	(297)	(294)
Financing activities
Issuance of common stock, net	0	0
Dividends paid on common stock	0	0
Dividends paid to parent	(175)	(100)
Proceeds from issuance of short-term debt with original maturities greater than 90 days	0
Net increase (decrease) in short-term debt	253	0
Proceeds from issuance of long-term debt, net	0	0
Retirement of long-term debt	0	0
Changes in advances from affiliated companies	11	0
Contributions from parent	0	0
Other financing activities	(37)	(60)
Net cash provided (used) by financing activities	52	(160)
Net increase (decrease) in cash and cash equivalents	0	(117)
Cash and cash equivalents at beginning of period	21	231
Cash and cash equivalents at end of period	21	114
Other
Operating revenues
Operating revenues	0	0
Affiliate revenues	(59)	(74)
Total revenues	(59)	(74)
Operating expenses
Fuel used in electric generation	0	0
Purchased power	0	0
Operation and maintenance	(54)	(71)
Depreciation, amortization and accretion	0	0
Taxes other than on income	(2)	(4)
Other	0	0
Total operating expenses	(56)	(75)
Operating (loss) income	(3)	1
Other income (expense)
Interest income	0	0
Allowance for equity funds used during construction	0	0
Other, net	2	0
Total other income (expense), net	2	0
Interest charges
Interest charges	0	0
Allowance for borrowed funds used during construction	0	0
Total interest charges, net	0	0
(Loss) income from continuing operations before income tax and equity in earnings of consolidated subsidiaries	(1)	1
Income tax (benefit) expense	(2)	(2)
Equity in earnings of consolidated subsidiaries	(186)	(229)
Income from continuing operations	(185)	(226)
Discontinued operations, net of tax	0	0
Net income (loss)	(185)	(226)
Net income attributable to noncontrolling interests, net of tax	(1)	0
Net income attributable to controlling interests	(186)	(226)
Comprehensive income
Comprehensive income	(190)	(230)
Comprehensive (income) loss attributable to noncontrolling interests, net of tax	(1)	0
Comprehensive income attributable to controlling interests	(191)	(230)
ASSETS
Utility plant, net	85		87
Current assets
Cash and cash equivalents	0	0
Receivables, net	0		0
Notes receivable from affiliated companies	(242)		(272)
Regulatory assets	0		0
Derivative collateral posted	0		0
Prepayments and other current assets	(133)		(87)
Total current assets	(375)		(359)
Deferred debits and other assets
Investment in consolidated subsidiaries	(13,968)		(14,043)
Regulatory assets	0		0
Goodwill	3,655		3,655
Nuclear decommissioning trust funds	0		0
Other assets and deferred debits	(445)		(486)
Total deferred debits and other assets	(10,758)		(10,874)
Total assets	(11,048)		(11,146)
Equity
Common stock equity	(10,295)		(10,374)
Noncontrolling interests	0		0
Total equity	(10,295)		(10,374)
Preferred stock of subsidiaries	0		0
Long-term debt, affiliate	(36)		(36)
Long-term debt, net	0		0
Total capitalization	(10,331)		(10,410)
Current liabilities
Current portion of long-term debt	0		0
Short-term debt	0		0
Notes payable to affiliated companies	(242)		(272)
Derivative liabilities	0		0
Other current liabilities	(138)		(84)
Total current liabilities	(380)		(356)
Deferred credits and other liabilities
Noncurrent income tax liabilities	(415)		(458)
Regulatory liabilities	85		86
Other liabilities and deferred credits	(7)		(8)
Total deferred credits and other liabilities	(337)		(380)
Total capitalization and liabilities	(11,048)		(11,146)
Condensed Consolidating Statement of Cash Flows
Net cash provided (used) by operating activities	(282)	(428)
Investing activities
Gross property additions	0	0
Nuclear fuel additions	0	0
Purchases of available-for-sale securities and other investments	0	0
Proceeds from available-for-sale securities and other investments	0	0
Changes in advances to affiliated companies	(30)	12
Contributions to consolidated subsidiaries	0	10
Other investing activities	0	(2)
Net cash provided (used) by investing activities	(30)	20
Financing activities
Issuance of common stock, net	0	0
Dividends paid on common stock	0	0
Dividends paid to parent	283	428
Proceeds from issuance of short-term debt with original maturities greater than 90 days	0
Net increase (decrease) in short-term debt	0	0
Proceeds from issuance of long-term debt, net	0	0
Retirement of long-term debt	0	0
Changes in advances from affiliated companies	29	(11)
Contributions from parent	0	(10)
Other financing activities	0	1
Net cash provided (used) by financing activities	312	408
Net increase (decrease) in cash and cash equivalents	0	0
Cash and cash equivalents at beginning of period	0	0
Cash and cash equivalents at end of period	$ 0	$ 0