Consolidated Statements Of Comprehensive Income (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Net gain (loss) arising during the period, tax		$ (18)	$ 16
Tax on prior service credit adjustment			3
Amortization of net actuarial loss, tax	$ 4	$ 1	$ 3
Amortization of prior service credit, tax
Unrealized gain (loss) on investments, tax expense (tax benefit)	$ (1)	$ (1)	$ (1)
Consumers Energy Company [Member]
Net gain (loss) arising during the period, tax	2	(7)	4
Amortization of net actuarial loss, tax	2	1	2
Unrealized gain (loss) on investments, tax expense (tax benefit)	(1)	$ 2
Reclassification adjustments included in net income, tax	$ (3)		$ (1)