Income Taxes (Significant Components Of Income Tax Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current income taxes
Federal	$ (67)	$ 0	$ 0
State and local	0	6	9
Total Current Income Tax Expense	(67)	6	9
Deferred income taxes
Federal	112	368	200
State and local	58	36	47
Total Deferred Income Tax Expense	170	404	247
Deferred income tax credit	12	14	17
Tax expense	115	424	273
Consumers Energy Company
Current income taxes
Federal	6	159	9
State and local	13	17	22
Total Current Income Tax Expense	19	176	31
Deferred income taxes
Federal	60	120	227
State and local	51	29	45
Total Deferred Income Tax Expense	111	149	272
Deferred income tax credit	12	14	17
Tax expense	$ 142	$ 339	$ 320