Income Taxes (Significant Components Of Income Tax Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
State and Local	$ 6	$ 9	$ 24
Total Current Income Tax Expense	6	9	24
Federal, deferred income taxes	368	200	192
State and Local, deferred income taxes	36	47	36
Total Deferred Income Tax Expense	404	247	228
Deferred income tax credit	14	17	19
Tax Expense	424	273	271
Consumers Energy Company [Member]
Federal	159	9	66
State and Local	17	22	32
Total Current Income Tax Expense	176	31	98
Federal, deferred income taxes	120	227	153
State and Local, deferred income taxes	29	45	32
Total Deferred Income Tax Expense	149	272	185
Deferred income tax credit	14	17	19
Tax Expense	$ 339	$ 320	$ 302