Income Taxes (Details 2) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Deferred Tax Liability Not Recognized [Line Items]
Property, plant and equipment	$ (2,578)	$ (2,285)
Securitized regulatory assets	(261)	(384)
Pension and benefits	73	67
Other comprehensive income	15	15
Other, net	(24)	(182)
Deferred Tax Assets Liabilities Gross	(2,775)	(2,769)
Current deferred income tax Liability (included in Current Liabilities - Other)	(14)	(68)
Long-term deferred income tax liability	(2,761)	(2,701)
Deferred income tax assets	557	608
Deferred income tax liabilities	$ (3,332)	$ (3,377)