Income Taxes (Details Textuals) (USD $)	3 Months Ended	12 Months Ended
	Jun. 30, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Jun. 30, 2010
Federal and State Income Tax [Line Items]
Production Tax Credits Earned In Prior Years But Not Utilized Carried Forward Indefinitely As Alternative Minimum Tax Credits		$ 254,000,000
Deferred Tax Assets State Net Operating Loss and Credit Carry Forwards 1		37,000,000		30,000,000
Valuation Allowance, Amount		33,000,000		27,000,000
Unrecognized Tax Benefits that Would Impact Effective Tax Rate		3,000,000		4,000,000
Time Period of Unrecognized Tax Benefits that Would Impact Effective Tax Rate		12 months
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit		1,000,000
Unrecognized Tax Benefits, Interest on Income Taxes Accrued		1,000,000		2,000,000
Unrecognized Tax Benefits, Income Tax Penalties Accrued		0
Unrecognized Tax Benefits, Interest on Income Taxes Expense		(1,000,000)	(2,000,000)	1,000,000
Michigan Corporate Income Tax	6.00%
Time Period for the MBT Deferred Tax Asset		1 year
Deferred Tax Liabilities Attributable to Regulated Utilities					36,000,000
Reduction of Net Deferred Tax Assets	0
Reduction of Net Deferred Tax Assets1	308,000,000
Decrease in Deferred Tax Liabilities Attributaable to Regulated Utilities	395,000,000
Income Tax Expense (Benefit)	87,000,000	286,000,000	268,000,000	315,000,000
Consistnet with Orginal Treatment of Deferred Tax Liabilities No Cash Flow Impact	0
Settlement with Taxing Authority [Member]
Federal and State Income Tax [Line Items]
Unrecognized Tax Benefits, Increases Resulting from Prior Period Tax Positions		$ 30,000,000