Financings and Capitalization (Narrative) (Details) (USD $)		3 Months Ended		3 Months Ended	23 Months Ended
	Mar. 31, 2013	Mar. 31, 2013 CMS Energy [Member]	Mar. 31, 2013 Consumers Energy Company [Member]	Mar. 31, 2013 Short-Term Borrowings [Member] Consumers Energy Company [Member]	Apr. 25, 2013 Continuous Equity Program [Member]	Mar. 31, 2013 Senior Notes 5.5% Due June 2029 [Member]
Financing And Capitalization [Line Items]
Amount of Facility				$ 250,000,000
Accounts receivable sales facility, current borrowing capacity				250,000,000
Average short-term borrowings				20,000,000
Weighted average annual interest rate				0.94%
Number of trading days, adjusted trigger price contingencies were met						20 days
Number of trading days						30 days
Limitation on payment of stock dividends	3,300,000,000
Unrestricted retained earnings			605,000,000
Common stock dividends from Consumers		93,000,000
Aggregate sales price of an equity offering program					$ 50,000,000