Accumulated Other Comprehensive Income (Loss), Net of Tax (Changes of AOCI) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Jun. 30, 2014	Sep. 30, 2014	Sep. 30, 2013
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	$ (73)	$ (362)	$ (95)	$ (95)	$ (388)
Other Comprehensive Income before Reclassifications	(13)	28		17	54
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(13)	(4)		(21)	(4)
Other Comprehensive Income (Loss), net of tax	(26)	24		(4)	50
Accumulated Other Comprehensive Income (Loss), Ending Balance	(99)	(338)		(99)	(338)
Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	1	3	(2)	(2)	7
Other Comprehensive Income before Reclassifications	2	1	(4)	(2)	1
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(1)	(2)	7	6	(6)
Other Comprehensive Income (Loss), net of tax	1	(1)		4	(5)
Accumulated Other Comprehensive Income (Loss), Ending Balance	2	2	1	2	2
Pension and OPEB Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	(232)	(466)	(238)	(238)	(485)
Other Comprehensive Income before Reclassifications	0	0		0	0
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	3	9		9	28
Other Comprehensive Income (Loss), net of tax	3	9		9	28
Accumulated Other Comprehensive Income (Loss), Ending Balance	(229)	(457)		(229)	(457)
Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	158	101	145	145	90
Other Comprehensive Income before Reclassifications	(15)	27		19	53
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(15)	(11)		(36)	(26)
Other Comprehensive Income (Loss), net of tax	(30)	16		(17)	27
Accumulated Other Comprehensive Income (Loss), Ending Balance	128	117		128	117
Power [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	(44)	(303)	(63)	(63)	(328)
Other Comprehensive Income before Reclassifications	(12)	29		15	57
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(15)	(5)		(23)	(8)
Other Comprehensive Income (Loss), net of tax	(27)	24		(8)	49
Accumulated Other Comprehensive Income (Loss), Ending Balance	(71)	(279)		(71)	(279)
Power [Member] | Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	2	4	(1)	(1)	9
Other Comprehensive Income before Reclassifications	2	1		(2)	1
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(1)	(2)		6	(7)
Other Comprehensive Income (Loss), net of tax	1	(1)		4	(6)
Accumulated Other Comprehensive Income (Loss), Ending Balance	3	3		3	3
Power [Member] | Pension and OPEB Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	(199)	(405)	(204)	(204)	(422)
Other Comprehensive Income before Reclassifications	0	0		0	0
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	2	8		7	25
Other Comprehensive Income (Loss), net of tax	2	8		7	25
Accumulated Other Comprehensive Income (Loss), Ending Balance	(197)	(397)		(197)	(397)
Power [Member] | Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	153	98	142	142	85
Other Comprehensive Income before Reclassifications	(14)	28		17	56
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(16)	(11)		(36)	(26)
Other Comprehensive Income (Loss), net of tax	(30)	17		(19)	30
Accumulated Other Comprehensive Income (Loss), Ending Balance	$ 123	$ 115		$ 123	$ 115