Contingencies And Commitments (Guarantees) (Details) - USD ($) $ in Millions		3 Months Ended		12 Months Ended
		Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Guarantor Obligations [Line Items]
Interest expense reduction		$ (7)	$ (6)
Interest income		1	1
Consumers Energy Company [Member]
Guarantor Obligations [Line Items]
Interest expense reduction		(3)	(3)
Interest income		$ 1	$ 1
Consumers Energy Company [Member] | Settlement with Taxing Authority [Member]
Guarantor Obligations [Line Items]
Tax examination refund				$ 37
PPE reduction resulting from tax refund				19
Interest expense reduction				12
Interest income				$ 6
Guarantees [Member]
Guarantor Obligations [Line Items]
Guarantee Description	[1]	Guarantees2
Expiration Date	[1]	Indefinite
Maximum obligation	[1]	$ 49
Guarantees [Member] | Consumers Energy Company [Member]
Guarantor Obligations [Line Items]
Guarantee Description	[1]	Gurarantee2
Expiration Date	[1]	Indefinite
Maximum obligation	[1]	$ 30
Indemnity Obligations From Asset Sales And Other Agreements [Member]
Guarantor Obligations [Line Items]
Guarantee Description	[2]	Indemnity obligations from asset sales   and other agreements1
Expiration Date	[2]	Indefinite
Maximum obligation	[2]	$ 153
Carrying Amount	[2]	7
Tax And Other Indemnity Obligations [Member] | Consumers Energy Company [Member] | Maximum [Member]
Guarantor Obligations [Line Items]
Carrying Amount		$ 1

[1] At Consumers, this obligation comprises a guarantee provided to the DOE in connection with a settlement agreement regarding damages resulting from the DOE'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 DOE 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.