Accumulated Other Comprehensive Income (Loss), Net of Tax (Reclassifications of AOCI) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Operating Revenues	$ 2,554	$ 2,402	$ 7,650	$ 7,375
Interest Expense	100	106	303	310
Income (Loss) from Continuing Operations before Income Taxes	660	588	1,751	1,650
Tax (Expense) Benefit	(270)	(241)	(708)	(599)
Net Income (Loss)	390	347	1,043	1,051
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Income (Loss) from Continuing Operations before Income Taxes	11		17
Tax (Expense) Benefit	(7)		(13)
Net Income (Loss)	4		4
Energy Related Contracts [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Operating Revenues	3		11
Tax (Expense) Benefit	(1)		(4)
Net Income (Loss)	2		7
Interest Rate Swap [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Interest Expense	0		(1)
Tax (Expense) Benefit	0		0
Net Income (Loss)	0		(1)
Pension and OPEB Plans [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Amortization of Prior Service Cost, Pre-Tax	3		8
Amortization of Prior Service Cost, Tax	(1)		(3)
Amortization of Prior Service Cost, After-Tax	2		5
Amortization of Actuarial Loss, Pre-Tax	(18)		(56)
Amortization of Actuarial Loss, Tax	7		23
Amortization of Actuarial Loss, After-Tax	(11)		(33)
Available-for-Sale Securities [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Realized Gains, Pre-Tax	35		99
Realized Gains, Tax	(18)		(51)
Realized Gains. After-Tax	17		48
Realized Losses, Pre-Tax	(9)		(37)
Realized Losses, Tax	4		18
Realized Losses, After-Tax	(5)		(19)
Other-Than-Temporary Impairments, Pre-Tax	(3)		(7)
Other-Than-Temporary Impairments, Tax	2		4
Other-Than-Temporary Impairments, After-Tax	(1)		(3)
Power [Member]
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Operating Revenues	1,169	1,038	3,806	3,584
Interest Expense	26	35	85	97
Income (Loss) from Continuing Operations before Income Taxes	374	314	945	912
Tax (Expense) Benefit	(153)	(133)	(383)	(374)
Net Income (Loss)	221	181	562	538
Power [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Income (Loss) from Continuing Operations before Income Taxes	12		23
Tax (Expense) Benefit	(7)		(15)
Net Income (Loss)	5		8
Power [Member] | Energy Related Contracts [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Operating Revenues	3		11
Tax (Expense) Benefit	(1)		(4)
Net Income (Loss)	2		7
Power [Member] | Pension and OPEB Plans [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Amortization of Prior Service Cost, Pre-Tax	3		7
Amortization of Prior Service Cost, Tax	(1)		(3)
Amortization of Prior Service Cost, After-Tax	2		4
Amortization of Actuarial Loss, Pre-Tax	(17)		(49)
Amortization of Actuarial Loss, Tax	7		20
Amortization of Actuarial Loss, After-Tax	(10)		(29)
Power [Member] | Available-for-Sale Securities [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Realized Gains, Pre-Tax	35		95
Realized Gains, Tax	(18)		(49)
Realized Gains. After-Tax	17		46
Realized Losses, Pre-Tax	(9)		(34)
Realized Losses, Tax	4		17
Realized Losses, After-Tax	(5)		(17)
Other-Than-Temporary Impairments, Pre-Tax	(3)		(7)
Other-Than-Temporary Impairments, Tax	2		4
Other-Than-Temporary Impairments, After-Tax	$ (1)		$ (3)