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]
Tax Payable to or Receivable from Parent		$ 13,000,000	$ 48,000,000
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
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		(3,000,000)	1,000,000	1,000,000
Unrecognized Tax Benefits, Increases Resulting from Prior Period Tax Positions		0	45,000,000	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					30,000,000
Reduction of Net Deferred Tax Assets	0
Decrease in Deferred Tax Liabilities Attributaable to Regulated Utilities	342,000,000
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		$ 52,000,000