Income Taxes (Significant Components Of Income Tax Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
State and Local	$ 24	$ 24	$ 34
Total Current Income Tax Expense	24	24	34
Federal, deferred income taxes	192	198	248
State and Local, deferred income taxes	36	31	23
Total Deferred Income Tax Expense	228	229	271
Deferred income tax credit	19	(3)	(3)
Tax Expense	271	250	302
Consumers Energy Company [Member]
Federal	66	8	137
State and Local	32	36	45
Total Current Income Tax Expense	98	44	182
Federal, deferred income taxes	153	236	147
State and Local, deferred income taxes	32	29	20
Total Deferred Income Tax Expense	185	265	167
Deferred income tax credit	19	(3)	(3)
Tax Expense	$ 302	$ 306	$ 346