Regulatory Matters (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Regulatory Asset and Liability [Line Items]
Regulatory Assets	$ 4,853	$ 4,158
Regulatory Assets, Current	(314)	(100)
Regulatory Assets, Noncurrent	4,539	4,058
Securitized Regulatory Assets, Noncurrent	577	729
Regulatory Liabilities	1,073	1,422
Regulatory Liability, Current	(54)	(94)
Regulatory Liability, Noncurrent	1,019	1,328
Asset Removal Costs [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Liabilities	419	479
Deferred Income Taxes [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Liabilities	0	418
Renewable Energy [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Liabilities	192	125
Refundable Revenue Decoupling [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Liabilities	127	47
Pension Cost [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Liabilities	120	129
Refundable Income Taxes [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Liabilities	66	77
Energy Optimization [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Liabilities	34	27
Refundable Uncollectible Expense [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Liabilities	31	0
Accrued PSCR GCR Refund [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Liabilities	26	8
Low Income Energy Efficiency Fund [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Liabilities	26	0
Refueling Outage [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Liabilities	23	3
Revenue Subject to Refund [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Liabilities	1	52
Refundable Costs Under PA 141 [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Liabilities	0	33
Refundable Restoration Expense [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Liabilities	0	15
Other Liabilities [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Liabilities	8	9
Pension [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Assets	2,208	1,742
Postretirment costs [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Assets	778	624
Asset retirement obligation [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Assets	420	336
Recoverable Michigan income taxes [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Assets	324	383
Recoverable income taxes related to securitized regulatory assets [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Assets	316	400
Choice incentive mechanism [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Assets	166	105
Accrued PSCR/GCR revenue [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Assets	147	52
Cost to Achieve Performance Excellence Process [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Assets	116	137
Other recoverabe income taxes [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Assets	81	85
Unamortized loss on reacquired debt [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Assets	64	65
Recoverable restoration expense [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Assets	58	19
Deferred environmental costs [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Assets	49	41
Recoverable uncollectible expense [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Assets	42	90
Enterprise Business Systems Costs [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Assets	18	21
Recoverable revenue decoupling [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Assets	18	5
Other [Member]
Regulatory Asset and Liability [Line Items]
Regulatory Assets	$ 48	$ 53