Accumulated Other Comprehensive Income (Loss), Net of Tax (Changes of AOCI) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended			6 Months Ended
	Jun. 30, 2014	Mar. 31, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	$ (87)	$ (95)	$ (355)	$ (95)	$ (388)
Other Comprehensive Income before Reclassifications	24		(16)	30	11
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(10)		9	(8)	15
Other Comprehensive Income (Loss), net of tax	14		(7)	22	26
Accumulated Other Comprehensive Income (Loss), Ending Balance	(73)		(362)	(73)	(362)
Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	0	(2)	3	(2)	7
Other Comprehensive Income before Reclassifications	1	(5)	0	(4)	0
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	0	7	0	7	(4)
Other Comprehensive Income (Loss), net of tax	1		0	3	(4)
Accumulated Other Comprehensive Income (Loss), Ending Balance	1	0	3	1	3
Pension and OPEB Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	(234)	(238)	(475)	(238)	(485)
Other Comprehensive Income before Reclassifications	0		0	0	0
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	2		9	6	19
Other Comprehensive Income (Loss), net of tax	2		9	6	19
Accumulated Other Comprehensive Income (Loss), Ending Balance	(232)		(466)	(232)	(466)
Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	147	145	117	145	90
Other Comprehensive Income before Reclassifications	23		(16)	34	11
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(12)		0	(21)	0
Other Comprehensive Income (Loss), net of tax	11		(16)	13	11
Accumulated Other Comprehensive Income (Loss), Ending Balance	158		101	158	101
Power [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	(57)	(63)	(296)	(63)	(328)
Other Comprehensive Income before Reclassifications	23		(14)	27	13
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(10)		7	(8)	12
Other Comprehensive Income (Loss), net of tax	13		(7)	19	25
Accumulated Other Comprehensive Income (Loss), Ending Balance	(44)		(303)	(44)	(303)
Power [Member] | Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	0	(1)	5	(1)	9
Other Comprehensive Income before Reclassifications	2		0	(4)	0
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	0		(1)	7	(5)
Other Comprehensive Income (Loss), net of tax	2		(1)	3	(5)
Accumulated Other Comprehensive Income (Loss), Ending Balance	2		4	2	4
Power [Member] | Pension and OPEB Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	(201)	(204)	(413)	(204)	(422)
Other Comprehensive Income before Reclassifications	0		0	0	0
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	2		8	5	17
Other Comprehensive Income (Loss), net of tax	2		8	5	17
Accumulated Other Comprehensive Income (Loss), Ending Balance	(199)		(405)	(199)	(405)
Power [Member] | Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	144	142	112	142	85
Other Comprehensive Income before Reclassifications	21		(14)	31	13
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(12)		0	(20)	0
Other Comprehensive Income (Loss), net of tax	9		(14)	11	13
Accumulated Other Comprehensive Income (Loss), Ending Balance	$ 153		$ 98	$ 153	$ 98