Regulatory Matters (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Regulatory Asset and Liability [Line Items]
Regulatory Assets	$ 3,510	$ 3,890
Regulatory Assets, Current	(162)	(272)
Regulatory Assets, Noncurrent	3,348	3,618
Securitized Regulatory Assets, Noncurrent	413	577
Regulatory Liabilities	549	534
Regulatory Liability, Current	(66)	(80)
Regulatory Liability, Noncurrent	483	454
Renewable Energy [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Liabilities	230	192
Refundable Revenue Decoupling [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Liabilities	127	127
Asset Removal Costs [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Liabilities	81	73
Over Recovery of Securitization [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Liabilities	54	53
Energy Optimization [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Liabilities	26	24
Refueling Outage [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Liabilities	12	23
Refundable Uncollectible Expense [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Liabilities	10	13
Low Income Energy Efficiency Fund [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Liabilities	0	23
Other Liabilities [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Liabilities	9	6
Pension [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Assets	1,815	1,656
Postretirment costs [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Assets	316	582
Asset retirement obligation [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Assets	424	420
Recoverable Michigan Income Taxes [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Assets	253	270
Recoverable income taxes related to securitized regulatory assets [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Assets	226	316
Accrued PSCR Revenue [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Assets	87	147
Cost to Achieve Performance Excellence Process [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Assets	82	100
Other recoverabe income taxes [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Assets	76	81
Choice Incentive Mechanism [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Assets	66	166
Recoverable restoration expense [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Assets	49	58
Unamortized loss on reacquired debt [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Assets	37	36
Enterprise Business Systems Costs [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Assets	16	18
Other [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Assets	$ 63	$ 40