Income Taxes (Significant Components Of Income Tax Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current income taxes
Federal	$ (31)	$ (67)	$ 0
State and local	28	0	6
Total Current Income Tax Expense	(3)	(67)	6
Deferred income taxes
Federal	97	112	368
State and local	32	58	36
Total Deferred Income Tax Expense	129	170	404
Deferred income tax credit	21	12	14
Tax expense	147	115	424
Consumers Energy Company
Current income taxes
Federal	107	6	159
State and local	41	13	17
Total Current Income Tax Expense	148	19	176
Deferred income taxes
Federal	(10)	60	120
State and local	26	51	29
Total Deferred Income Tax Expense	16	111	149
Deferred income tax credit	21	12	14
Tax expense	$ 185	$ 142	$ 339