Income Taxes (Significant Components Of Income Tax Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Current income taxes
Federal	$ (35)	$ (31)	$ (67)
State and local	(2)	28	0
Total Current Income Tax Expense	(37)	(3)	(67)
Deferred income taxes
Federal	115	97	112
State and local	60	32	58
Total Deferred Income Tax Expense	175	129	170
Deferred income tax credit	(5)	21	12
Income tax expense	133	147	115
Consumers Energy Company
Current income taxes
Federal	3	107	6
State and local	(7)	41	13
Total Current Income Tax Expense	(4)	148	19
Deferred income taxes
Federal	115	(10)	60
State and local	67	26	51
Total Deferred Income Tax Expense	182	16	111
Deferred income tax credit	(5)	21	12
Income tax expense	$ 173	$ 185	$ 142