Regulatory Matters (Schedule of Regulatory Assets) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Regulatory Assets [Line Items]
Regulatory Assets	$ 2,863	$ 4,417
Regulatory Assets, Current	(26)	(182)
Regulatory Assets, Noncurrent	2,837	4,235
Securitized Regulatory Assets, Noncurrent	231	413
Pension Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	1,660	2,420
Postretirment Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	426
Asset Retirement Obligation Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	394	424
Recoverable Michigan Income Taxes [Member]
Regulatory Assets [Line Items]
Regulatory Assets	286	304
Recoverable Income Taxes related to Securitized Regulatory Assets [Member]
Regulatory Assets [Line Items]
Regulatory Assets	126	226
Cost to Achieve Performance Excellence Process [Member]
Regulatory Assets [Line Items]
Regulatory Assets	75	96
Other Recoverabe Income Taxes [Member]
Regulatory Assets [Line Items]
Regulatory Assets	71	76
Unamortized Loss on Reacquired Debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets	63	63
Environmental Restoration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	59	58
Enterprise Business Systems Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	13	16
Regulatory Clause Revenues, under-recovered [Member]
Regulatory Assets [Line Items]
Regulatory Assets	9	28
Choice Incentive Mechanism [Member]
Regulatory Assets [Line Items]
Regulatory Assets	3	66
Accrued PSCRandGCR Revenue [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	87
Recoverable Restoration Expense [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	49
Other Assets [Member]
Regulatory Assets [Line Items]
Regulatory Assets	$ 104	$ 78