Asset Sales, Discontinued Operations, And Impairment Charges (Asset Sales) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2010
Gains (Losses) on Sales of Assets	$ 1	$ 6
CMS Generation San Nicolas Company [Member]
Gains (Losses) on Sales of Assets		3
Cost-Method Investment [Member]
Gains (Losses) on Sales of Assets		3
Cost Method Investment Sold Carrying Amount		$ 0

The net gain (loss) resulting from the sale, transfer, termination, or other disposition of assets during the period, excluding transactions involving capital leases, assets-held- or available-for-lease, and other real estate owned which, to the extent appropriate, are included in gains (losses) on the disposition of assets in nonoperating income (expense).

No definition available.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration