Consolidated Statements Of Comprehensive Income (Parenthetical) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Retirement benefits liability adjustments, tax expense (tax benefit)		$ 1		$ 1
Unrealized gain (loss) on investments, tax expense (tax benefit)	1		1
Consumers Energy Company [Member]
Retirement benefits liability adjustments, tax expense (tax benefit)
Unrealized gain (loss) on investments, tax expense (tax benefit)	$ 1		$ (1)	$ (1)