Financings and Capitalization (Short-term Borrowings) (Details) (Consumers Energy Company [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Maximum outstanding during the period	$ 0	$ 50
Average short-term borrowings		1
Weighted average annual interest rate		0.20%
Short-term Borrowings [Member]
Accounts receivable sales facility, maximum borrowing capacity	250
Accounts receivable sales facility, current borrowing capacity	$ 250