Income Taxes (Details Textuals) (USD $)	3 Months Ended	12 Months Ended
	Jun. 30, 2011 percent	Dec. 31, 2011 months	Dec. 31, 2010	Dec. 31, 2009	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		$ 294,000,000
Deferred Tax Assets State Net Operating Loss and Credit Carry Forwards 1		30,000,000	33,000,000
Valuation Allowance, Amount		27,000,000	32,000,000
Unrecognized Tax Benefits that Would Impact Effective Tax Rate		4,000,000	5,000,000
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit		31,000,000
Time Period of Unrecognized Tax Benefits that Would Impact Effective Tax Rate		12
Unrecognized Tax Benefits, Interest on Income Taxes Accrued		2,000,000	3,000,000
Unrecognized Tax Benefits, Income Tax Penalties Accrued		0
Unrecognized Tax Benefits, Interest on Income Taxes Expense		(2,000,000)	1,000,000	(2,000,000)
Unrecognized Tax Benefits, Increases Resulting from Prior Period Tax Positions			53,000,000
Michigan Corporate Income Tax	6.00%
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	267,000,000	311,000,000	247,000,000
Consistnet with Orginal Treatment of Deferred Tax Liabilities No Cash Flow Impact	$ 0