Accumulated Other Comprehensive Income (Loss), Net of Tax Accumulated Other Comprehensive Income (Loss), Net of Tax (Changes in AOCI) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	$ (95)	$ (388)
Other Comprehensive Income before Reclassifications	(135)	299
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(53)	(6)
Net Current Period Other Comprehensive Income (Loss)	(188)	293	(51)
Ending Balance	(283)	(95)	(388)
Power [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	(63)	(328)
Other Comprehensive Income before Reclassifications	(110)	276
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(55)	(11)
Net Current Period Other Comprehensive Income (Loss)	(165)	265	(52)
Ending Balance	(228)	(63)	(328)
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	(2)	7
Other Comprehensive Income before Reclassifications	7	(2)
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	5	(7)
Net Current Period Other Comprehensive Income (Loss)	12	(9)
Ending Balance	10	(2)
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Power [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	(1)	9
Other Comprehensive Income before Reclassifications	7	(2)
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	5	(8)
Net Current Period Other Comprehensive Income (Loss)	12	(10)
Ending Balance	11	(1)
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	(238)	(485)
Other Comprehensive Income before Reclassifications	(184)	210
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	11	37
Net Current Period Other Comprehensive Income (Loss)	(173)	247
Ending Balance	(411)	(238)
Accumulated Defined Benefit Plans Adjustment [Member] | Power [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	(204)	(422)
Other Comprehensive Income before Reclassifications	(156)	185
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	9	33
Net Current Period Other Comprehensive Income (Loss)	(147)	218
Ending Balance	(351)	(204)
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	145	90
Other Comprehensive Income before Reclassifications	42	91
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(69)	(36)
Net Current Period Other Comprehensive Income (Loss)	(27)	55
Ending Balance	118	145
Accumulated Net Unrealized Investment Gain (Loss) [Member] | Power [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	142	85
Other Comprehensive Income before Reclassifications	39	93
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(69)	(36)
Net Current Period Other Comprehensive Income (Loss)	(30)	57
Ending Balance	$ 112	$ 142