Consolidated Statements Of Comprehensive Income (Parenthetical) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Net gain (loss) arising during the period, tax	$ (18)	$ 16	$ (7)
Tax on prior service credit adjustment		3
Amortization of net actuarial loss, tax	1	3	1
Unrealized gain (loss) on investments, tax expense (tax benefit)	(1)	(1)	1
Consumers Energy Company [Member]
Net gain (loss) arising during the period, tax	(7)	4	(5)
Amortization of net actuarial loss, tax	1	2	1
Unrealized gain (loss) on investments, tax expense (tax benefit)	2		2
Reclassification adjustments included in net income, tax		$ (1)	$ (2)