Financings and Capitalization (Short-term Borrowings) (Details) (Short-term Borrowings [Member], Consumers Energy Company [Member], USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2012
Short-term Borrowings [Member] | Consumers Energy Company [Member]
Accounts receivable sales facility, maximum borrowing capacity	$ 250
Accounts receivable sales facility, current borrowing capacity	250
Maximum outstanding during the period	0
Average short-term borrowings	$ 16
Weighted average annual interest rate	0.90%