Regulatory Matters (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Regulatory Asset and Liability [Line Items]
Regulatory Assets	$ 4,417	$ 4,853
Regulatory Assets, Current	(182)	(314)
Regulatory Assets, Noncurrent	4,235	4,539
Securitized Regulatory Assets, Noncurrent	413	577
Regulatory Liabilities	1,120	1,126
Regulatory Liability, Current	(89)	(107)
Regulatory Liability, Noncurrent	1,031	1,019
Asset Removal Costs [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Liabilities	439	419
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
Pension Cost [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Liabilities	105	120
Refundable Income Taxes [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Liabilities	56	66
Over Recovery of Securitization [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Liabilities	54	53
Refundable Uncollectible Expense [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Liabilities	37	31
Energy Optimization [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Liabilities	34	34
Accrued PSCR GCR Refund [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Liabilities	16	26
Refueling Outage [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Liabilities	12	23
Low Income Energy Efficiency Fund [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Liabilities	0	26
Other Liabilities [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Liabilities	10	9
Pension [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Assets	2,420	2,208
Postretirment costs [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Assets	426	778
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	304	324
Recoverable income taxes related to securitized regulatory assets [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Assets	226	316
Cost to Achieve Performance Excellence Process [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Assets	96	116
Accrued PSCR/GCR revenue [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Assets	87	147
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
Loss on Reacquired Debt [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Assets	63	64
Deferred environmental costs [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Assets	58	49
Recoverable restoration expense [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Assets	49	58
Recoverable revenue decoupling [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Assets	28	18
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	$ 78	$ 90