Regulatory Matters (Schedule of PSCR Reconciliation Filings Pending with the MPSC) (Details) (Power Supply Cost Recover (PSCR) [Member], Consumers Energy Company [Member], USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Power Supply Cost Recover (PSCR) [Member] | Consumers Energy Company [Member]
Regulatory Matters [Line Items]
Date of Filing	March 2013
Net Over Under Recovery Of Expense Including Interest Requested	$ (18,000,000)
PSCR Cost of Power Sold	$ 1,900,000,000	$ 1,800,000,000