Consolidated Statements Of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Net Income	$ 752	$ 682	$ 659
Retirement Benefits Liability
Net loss arising during the period, net of tax	(15)	(7)	(4)
Settlement arising during the period, net of tax	1	0	0
Prior service credit adjustment, net of tax	(1)	0	(1)
Amortization of net actuarial loss, net of tax	5	3	4
Amortization of prior service credit, net of tax	(1)	(2)	(1)
Derivatives
Unrealized loss on derivative instruments, net of tax of $(2), $(1), and $—	(4)	(3)	(2)
Reclassification adjustments included in net income, net of tax of $— for all periods	2	1	0
Other Comprehensive Loss	(13)	(8)	(4)
Comprehensive Income	739	674	655
Comprehensive Income (Loss) Attributable to Noncontrolling Interests	(3)	2	2
Comprehensive Income Attributable to CMS Energy	742	672	653
Consumers Energy Company
Net Income	816	743	705
Retirement Benefits Liability
Net loss arising during the period, net of tax	(9)	(8)	6
Amortization of net actuarial loss, net of tax	1	1	2
Investments
Unrealized gain on investments, net of tax	0	0	(1)
Reclassification adjustments included in net income, net of tax	0	0	1
Derivatives
Other Comprehensive Loss	(8)	(7)	8
Comprehensive Income	$ 808	$ 736	$ 713