Asset Retirement Obligations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO Liability, at beginning of period	$ 477	$ 432
Incurred	65	55
Settled	(41)	(38)
Accretion	24	21
Cash Flow Revisions	28	7
ARO Liability, end of period	553	477
Consumers Energy Company
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO Liability, at beginning of period	474	428
Incurred	46	55
Settled	(41)	(37)
Accretion	23	21
Cash Flow Revisions	28	7
ARO Liability, end of period	530	474
Gas treating plant and gas wells
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO Liability, at beginning of period	0	1
Incurred		0
Settled		(1)
Accretion		0
Cash Flow Revisions		0
ARO Liability, end of period		0
Renewable generation assets
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO Liability, at beginning of period	3	3
Incurred	19	0
Settled	0	0
Accretion	1	0
Cash Flow Revisions	0	0
ARO Liability, end of period	23	3
Renewable generation assets | Consumers Energy Company
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO Liability, at beginning of period	21	11
Incurred	24	10
Settled	0	0
Accretion	1	0
Cash Flow Revisions	28	0
ARO Liability, end of period	74	21
Coal ash disposal areas | Consumers Energy Company
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO Liability, at beginning of period	166	179
Incurred	0	0
Settled	(24)	(27)
Accretion	6	7
Cash Flow Revisions	0	7
ARO Liability, end of period	148	166
Gas distribution cut, purge, and cap | Consumers Energy Company
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO Liability, at beginning of period	231	205
Incurred	1	22
Settled	(5)	(8)
Accretion	13	12
Cash Flow Revisions	0	0
ARO Liability, end of period	240	231
Asbestos abatement | Consumers Energy Company
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO Liability, at beginning of period	34	33
Incurred	0	0
Settled	0	(1)
Accretion	2	2
Cash Flow Revisions	0	0
ARO Liability, end of period	36	34
Gas wells plug and abandon | Consumers Energy Company
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO Liability, at beginning of period	22	0
Incurred	16	23
Settled	(7)	(1)
Accretion	1	0
Cash Flow Revisions	0	0
ARO Liability, end of period	32	22
Cable under Straits of Mackinac | Consumers Energy Company
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO Liability, at beginning of period	0
Incurred	5
Settled	(5)
Accretion	0
Cash Flow Revisions	0
ARO Liability, end of period	$ 0	$ 0