Consolidated Statements Of Comprehensive Income (Parenthetical) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Retirement benefits liability adjustments, tax expense (tax benefit)	$ 1		$ 1
Unrealized gain (loss) on investments, tax expense (tax benefit)
Consumers Energy Company [Member]
Retirement benefits liability adjustments, tax expense (tax benefit)	1		1
Unrealized gain (loss) on investments, tax expense (tax benefit)	1		1	(2)
Reclassification adjustments included in net income, tax			$ (1)