Regulatory Matters (Regulatory Assets) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Regulatory Assets [Line Items]
Regulatory Assets	$ 2,288	$ 3,510
Regulatory Assets, Current	(13)	(162)
Regulatory Assets, Noncurrent	2,275	3,348
Securitized Regulatory Assets, Noncurrent	231	413
Pension Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	1,257	1,815
Postretirement Benefit Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	316
Asset Retirement Obligation Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	394	424
Recoverable Michigan Income Taxes [Member]
Regulatory Assets [Line Items]
Regulatory Assets	237	253
Recoverable Income Taxes related to Securitized Regulatory Assets [Member]
Regulatory Assets [Line Items]
Regulatory Assets	126	226
Other Recoverabe Income Taxes [Member]
Regulatory Assets [Line Items]
Regulatory Assets	71	76
Cost to Achieve Performance Excellence Process [Member]
Regulatory Assets [Line Items]
Regulatory Assets	64	82
Loss on Reacquired Debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets	38	37
Enterprise Business Systems Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	13	16
Choice incentive mechanism [Member]
Regulatory Assets [Line Items]
Regulatory Assets	3	66
Accrued PSCR 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	$ 85	$ 63