Accumulated Other Comprehensive Income (Schedule of Reclassifications out of AOCI by Component Net of Tax) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Operating Revenue	$ 3,630	$ 3,523
Purchased gas	540	467
Electric fuel and other energy-related purchases	1,334	951
Interest and related charges	237	228
Other income	40	87
Income from continuing operations including noncontrolling interests before income tax expense	571	789
Income tax expense	(186)	(288)
Income from continuing operations including noncontrolling interests	385	501
Deferred gains and losses on derivatives-hedging activities | Amounts reclassified from AOCI
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income from continuing operations including noncontrolling interests before income tax expense	260	124
Income tax expense	(100)	(48)
Income from continuing operations including noncontrolling interests	160	76
Unrealized gains and losses on investment securities | Amounts reclassified from AOCI
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other income	(20)	(47)
Impairment	2	2
Income from continuing operations including noncontrolling interests before income tax expense	(18)	(45)
Income tax expense	7	18
Income from continuing operations including noncontrolling interests	(11)	(27)
Unrecognized pension and other postretirement benefit costs | Amounts reclassified from AOCI
Accumulated Other Comprehensive Income (Loss) [Line Items]
Prior service costs	(3)
Actuarial (gain) losses	17	29
Income from continuing operations including noncontrolling interests before income tax expense	14	29
Income tax expense	(6)	(9)
Income from continuing operations including noncontrolling interests	8	20
Commodity contracts | Deferred gains and losses on derivatives-hedging activities | Amounts reclassified from AOCI
Accumulated Other Comprehensive Income (Loss) [Line Items]
Operating Revenue	269	84
Purchased gas	1	34
Electric fuel and other energy-related purchases	(13)	3
Interest rate contracts | Deferred gains and losses on derivatives-hedging activities | Amounts reclassified from AOCI
Accumulated Other Comprehensive Income (Loss) [Line Items]
Interest and related charges	$ 3	$ 3