Retirement Benefits and Trusteed Assets (Details 10) (USD $) In Millions, unless otherwise specified	1 Months Ended	12 Months Ended
	Jan. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Change in Accumulated PostRetirement Benefit Obligation [Line Items]
Consolidation of VIEs		$ 0	$ 19	$ 0
Regulatory Assets		4,853	4,158
Other Postretirement Benefit Plans, Defined Benefit [Member]
Change in Accumulated PostRetirement Benefit Obligation [Line Items]
Benefit obligation, beginning of year	2,470	2,305	2,151
Consolidation of VIEs		0	21
Service cost		64	61	59
Interest cost		121	125	133
Plan amendments		(4)	(79)
Actuarial loss		80	127
Medicare Part D subsidy		6	7
Benefits paid		(102)	(108)
Benefit obligation, end of year		2,470	2,305	2,151
Defined Benefit Plan, Fair Value of Plan Assets		985	1,029	864
Actual return on plan assets		(22)	108
Company contributions	140	111	160
Benefits paid		(133)	(103)
Funded status of the plans		(1,485)	(1,276)
Current liabilities		(1)	(1)
Noncurrent liabilities		(1,484)	(1,275)
Pension and Other Postretirement Defined Benefit Plans, Liabilities		(1,485)	(1,276)
Net actuarial loss		47	46
Prior serice cost (credit)		(20)	(28)
Net transition obligation		(1)	(2)
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax		26	16
Net actuarial loss		835	692
Prior service cost		(60)	(74)
Net transition obligation		3	6
Regulatory Assets		$ 778	$ 624