Contingencies And Commitments (Guarantees) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2017 USD ($)
Guarantees [Member]
Guarantees And Other Contingencies [Line Items]
Guarantee Description	Guarantees	[1]
Expiration Date	Indefinite	[1]
Maximum obligation	$ 45	[1]
Guarantees [Member] | Consumers Energy Company [Member]
Guarantees And Other Contingencies [Line Items]
Guarantee Description	Guarantee	[1]
Expiration Date	Indefinite	[1]
Maximum obligation	$ 30	[1]
Indemnity Obligations From Stock And Asset Sales Agreements [Member]
Guarantees And Other Contingencies [Line Items]
Guarantee Description	Indemnity obligations from stock and asset sales agreements	[2]
Expiration Date	Indefinite	[2]
Maximum obligation	$ 153	[2]
Carrying Amount	7	[2]
Tax And Other Indemnity Obligations [Member] | Consumers Energy Company [Member]
Guarantees And Other Contingencies [Line Items]
Carrying Amount	$ 1

[1] At Consumers, this obligation comprises a guarantee provided to the U.S. Department of Energy in connection with a settlement agreement regarding damages resulting from the department's failure to accept spent nuclear fuel from nuclear power plants formerly owned by Consumers. At CMS Energy, the guarantee obligations comprise Consumers' guarantee to the U.S. Department of Energy and CMS Energy's 1994 guarantee of non-recourse revenue bonds issued by Genesee.

[2] These obligations arose from stock and asset sale agreements under which CMS Energy or a subsidiary of CMS Energy indemnified the purchaser for losses resulting from various matters, primarily claims related to taxes. CMS Energy believes the likelihood of material loss to be remote for the indemnity obligations not recorded as liabilities.