Income Taxes (Significant Components Of Income Tax Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
State and Local	$ 9	$ 24	$ 24
Total Current Income Tax Expense	9	24	24
Federal, deferred income taxes	200	192	198
State and Local, deferred income taxes	47	36	31
Total Deferred Income Tax Expense	247	228	229
Deferred income tax credit	17	19	(3)
Tax Expense	273	271	250
Consumers Energy Company [Member]
Federal	9	66	8
State and Local	22	32	36
Total Current Income Tax Expense	31	98	44
Federal, deferred income taxes	227	153	236
State and Local, deferred income taxes	45	32	29
Total Deferred Income Tax Expense	272	185	265
Deferred income tax credit	17	19	(3)
Tax Expense	$ 320	$ 302	$ 306