Financings And Capitalization (Short-Term Borrowings) (Details) (Short-Term Borrowings [Member], Consumers Energy Company [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012
Short-Term Borrowings [Member] | Consumers Energy Company [Member]
Accounts receivable sales facility, maximum borrowing capacity	$ 250
Accounts receivable sales facility, current borrowing capacity	140
Maximum outstanding during the period	110
Average short-term borrowings	$ 20
Weighted average annual interest rate	0.94%