Income Taxes (Details 2) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Deferred Tax Liability Not Recognized [Line Items]
Deferred Tax Liabilities, Property, Plant and Equipment	$ (3,131)	$ (2,558)
Deferred Tax Liabilities, Regulatory Assets	(360)	(396)
Deferred Tax Assets, Tax Credit Carryforwards, Alternative Minimum Tax	294	337
Deferred Tax Assets Merger Basis Differences	50	49
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits	(39)	(36)
Deferred Tax Assets, Other Comprehensive Loss	99	83
Deferred Tax Assets Liabilities Derivative	64	29
Deferred Tax Assets State Net Operating Loss and Credit Carry Forwards	30	33
Deferred Tax Assets, Other	(45)	(2)
Deferred Tax Assets Liabilities Gross	(3,038)	(2,461)
Deferred Tax Assets, Valuation Allowance	(27)	(32)
Deferred Tax Assets (Liabilities), Net	(3,065)	(2,493)
Deferred Tax Assets, Net, Current	51	139
Deferred Tax Liabilities, Noncurrent	(3,116)	(2,632)
Deferred Tax Assets, Net	1,048	1,418
Deferred Tax Liabilities	$ (4,113)	$ (3,911)