Contingencies And Commitments (Guarantees) (Details) $ in Millions		1 Months Ended	12 Months Ended
		Dec. 31, 2015 USD ($) $ / MWh MW	Dec. 31, 2015 USD ($) $ / MWh MW	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Guarantor Obligations [Line Items]
Interest expense reduction			$ (14)	$ (17)	$ (16)
Interest income			$ 12	5	3
Consumers Energy Company [Member]
Guarantor Obligations [Line Items]
Expiration Date	[1]		Indefinite
Maximum obligation	[1]	$ 30	$ 30
Interest expense reduction			(2)	(10)	(11)
Interest income			11	4	2
Consumers Energy Company [Member] | Settlement with Taxing Authority [Member]
Guarantor Obligations [Line Items]
Tax examination refund		37	37
Interest expense reduction		12
Interest income		6
PPE reduction resulting from tax refund		19
Reduction of income tax expense		5
Consumers Energy Company [Member] | Refund Of Taxes Paid Receivable [Member] | Settlement with Taxing Authority [Member]
Guarantor Obligations [Line Items]
Tax examination refund		19	19
Consumers Energy Company [Member] | Refund Of Interest Paid Receivable [Member] | Settlement with Taxing Authority [Member]
Guarantor Obligations [Line Items]
Tax examination refund		12	12
Consumers Energy Company [Member] | Interest Receivable [Member] | Settlement with Taxing Authority [Member]
Guarantor Obligations [Line Items]
Tax examination refund		6	$ 6
Guarantees [Member]
Guarantor Obligations [Line Items]
Expiration Date	[1]		Indefinite
Maximum obligation	[1]	51	$ 51
Indemnity Obligations From Asset Sales And Other Agreements [Member]
Guarantor Obligations [Line Items]
Expiration Date	[2]		Indefinite
Maximum obligation	[2]	143	$ 143
Carrying Amount	[2]	7	7
Tax And Other Indemnity Obligations [Member] | Consumers Energy Company [Member] | Maximum [Member]
Guarantor Obligations [Line Items]
Carrying Amount		1	1
MCV PPA [Member] | Consumers Energy Company [Member]
Guarantor Obligations [Line Items]
Purchase Obligations Total		3,003	3,003
Purchase Obligations Due in Year One		335	335
Purchase Obligations Due in Year Two		345	345
Purchase Obligations Due in Year Three		277	277
Purchase Obligations Due in Year Four		321	321
Purchase Obligations Due in Year Five		296	296
Purchase Obligations Due After Year Five		$ 1,429	$ 1,429
Term of Unrecorded Unconditional Purchase Obligations			35 years
Unrecorded Unconditional Purchase Obligations, Minimum Quantity Required | MW		1,240	1,240
Unrecorded Unconditional Purchase Obligation Capacity Charge Per Mwh | $ / MWh		10.14	10.14
Unrecorded Unconditional Purchase Obligation, Annual Contribution to Renewable Resources Program By Counterparty			$ 5
Unrecorded Unconditional Purchase Obligation, Contract Extension Period			5 years
Unrecorded Unconditional Purchase Obligation, Purchases			$ 282	300	278
Palisades PPA [Member] | Consumers Energy Company [Member]
Guarantor Obligations [Line Items]
Purchase Obligations Total		$ 2,327	2,327
Purchase Obligations Due in Year One		342	342
Purchase Obligations Due in Year Two		352	352
Purchase Obligations Due in Year Three		363	363
Purchase Obligations Due in Year Four		374	374
Purchase Obligations Due in Year Five		387	387
Purchase Obligations Due After Year Five		509	509
Unrecorded Unconditional Purchase Obligation, Purchases			$ 352	302	338
Unrecorded Unconditional Purchase Obligations, Maximum Quantity | MW			798
Related Parties PPA [Member] | Consumers Energy Company [Member]
Guarantor Obligations [Line Items]
Purchase Obligations Total		977	$ 977
Purchase Obligations Due in Year One		82	82
Purchase Obligations Due in Year Two		82	82
Purchase Obligations Due in Year Three		82	82
Purchase Obligations Due in Year Four		85	85
Purchase Obligations Due in Year Five		87	87
Purchase Obligations Due After Year Five		559	559
Other PPA [Member] | Consumers Energy Company [Member]
Guarantor Obligations [Line Items]
Purchase Obligations Total		3,640	3,640
Purchase Obligations Due in Year One		240	240
Purchase Obligations Due in Year Two		248	248
Purchase Obligations Due in Year Three		247	247
Purchase Obligations Due in Year Four		223	223
Purchase Obligations Due in Year Five		225	225
Purchase Obligations Due After Year Five		2,457	2,457
Unrecorded Unconditional Purchase Obligation, Purchases			347	$ 354	$ 345
PPA [Member] | Consumers Energy Company [Member]
Guarantor Obligations [Line Items]
Purchase Obligations Total		9,947	9,947
Purchase Obligations Due in Year One		999	999
Purchase Obligations Due in Year Two		1,027	1,027
Purchase Obligations Due in Year Three		969	969
Purchase Obligations Due in Year Four		1,003	1,003
Purchase Obligations Due in Year Five		995	995
Purchase Obligations Due After Year Five		4,954	4,954
Other Purchase Obligations [Member]
Guarantor Obligations [Line Items]
Purchase Obligations Total		2,200	2,200
Purchase Obligations Due in Year One		904	904
Purchase Obligations Due in Year Two		580	580
Purchase Obligations Due in Year Three		251	251
Purchase Obligations Due in Year Four		111	111
Purchase Obligations Due in Year Five		63	63
Purchase Obligations Due After Year Five		291	291
Other Purchase Obligations [Member] | Consumers Energy Company [Member]
Guarantor Obligations [Line Items]
Purchase Obligations Total		1,908	1,908
Purchase Obligations Due in Year One		870	870
Purchase Obligations Due in Year Two		551	551
Purchase Obligations Due in Year Three		224	224
Purchase Obligations Due in Year Four		83	83
Purchase Obligations Due in Year Five		34	34
Purchase Obligations Due After Year Five		$ 146	$ 146

[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. For additional details on this guarantee, see Note 19, Variable Interest Entities.

[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.