Income Taxes (The Companies Deferred Income Taxes Components) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Total deferred income tax assets	$ 2,229	$ 1,642
Total deferred income tax liabilities	7,424	6,233
Plant and equipment, primarily depreciation method and basis differences	4,008	3,027
Nuclear decommissioning	913	749
Deferred state income taxes	493	446
Federal benefit of deferred state income taxes	(173)	(156)
Deferred fuel, purchased energy and gas cots	161	120
Pension benefits	396	521
Other postretirement benefits	(167)	(186)
Loss and credit carryforwards	(577)	(181)
Reserve for rate proceedings	(54)	(56)
Partnership basis differences	274	265
Valuation allowances	96	68
Other	(175)	(26)
Total net deferred income tax liabilities	$ (5,195)	$ (4,591)