Contingencies And Commitments (Guarantees) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) $ / MW MW	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Guarantees
Guarantees And Other Contingencies [Line Items]
Expiration Date	indefinite
Maximum Obligation	$ 39
Carrying Amount	$ 0
Guarantees | Consumers Energy Company
Guarantees And Other Contingencies [Line Items]
Expiration Date	indefinite
Maximum Obligation	$ 30
Carrying Amount	$ 0
Indemnity Obligations From Stock And Asset Sales Agreements
Guarantees And Other Contingencies [Line Items]
Expiration Date	indefinite
Maximum Obligation	$ 153
Carrying Amount	3
Tax And Other Indemnity Obligations | Consumers Energy Company
Guarantees And Other Contingencies [Line Items]
Carrying Amount	1
MCV PPA | Consumers Energy Company
Guarantees And Other Contingencies [Line Items]
Total	3,880
2019	330
2020	318
2021	289
2022	275
2023	279
Beyond 2023	$ 2,389
Term of unrecorded PPA	35 years
PPA minimum quantity required | MW	1,240
PPA capacity charge per MWh (in dollars per MWh) | $ / MW	10.14
Annual contribution to renewable resources program by counterparty	$ 5
Contract extension period	5 years
Purchases	$ 353	$ 321	$ 305
Palisades PPA | Consumers Energy Company
Guarantees And Other Contingencies [Line Items]
Total	1,280
2019	378
2020	388
2021	400
2022	114
2023	0
Beyond 2023	0
Purchases	$ 375	366	363
Annual average capacity (in MW) | MW	798
Related-party PPAs | Consumers Energy Company
Guarantees And Other Contingencies [Line Items]
Total	$ 692
2019	85
2020	85
2021	86
2022	86
2023	87
Beyond 2023	263
Other PPAs | Consumers Energy Company
Guarantees And Other Contingencies [Line Items]
Total	4,078
2019	256
2020	260
2021	268
2022	269
2023	272
Beyond 2023	2,753
Purchases	350	$ 349	$ 348
Total PPAs | Consumers Energy Company
Guarantees And Other Contingencies [Line Items]
Total	9,930
2019	1,049
2020	1,051
2021	1,043
2022	744
2023	638
Beyond 2023	5,405
Other
Guarantees And Other Contingencies [Line Items]
Total	2,341
2019	1,276
2020	405
2021	163
2022	137
2023	117
Beyond 2023	243
Other | Consumers Energy Company
Guarantees And Other Contingencies [Line Items]
Total	2,075
2019	1,237
2020	373
2021	148
2022	124
2023	103
Beyond 2023	$ 90