Consolidated Balance Sheets (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Allowances for doubtful accounts receivable	$ 30	$ 35
Allowances for doubtful notes receivable	5	5
Common stock, shares authorized	350,000,000	350,000,000
Common stock, shares outstanding	263,900,000	254,100,000
Consumers Energy Company [Member]
Allowances for doubtful accounts receivable	$ 28	$ 33
Common stock, shares authorized	125,000,000	125,000,000
Common stock, shares outstanding	84,100,000	84,100,000