Leases and Palisades Financing - Assets and Liabilities of Lessee (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Operating leases
Right-of-use assets	$ 34	$ 47
Lease liabilities
Current lease liabilities	9	9
Noncurrent lease liabilities	25	37
Finance leases
Right-of-use assets	65	71
Lease liabilities
Finance lease liability	60
Current lease liabilities	7	6
Non-current lease liabilities	$ 53	$ 60
Weighted-average remaining lease term (in years)
Operating leases	19 years	17 years
Finance leases	12 years	12 years
Weighted-average discount rate
Operating leases	3.90%	3.80%
Finance leases	1.80%	1.90%
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:OtherAssetsNoncurrent
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesCurrent	us-gaap:OtherLiabilitiesCurrent
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesNoncurrent	us-gaap:OtherLiabilitiesNoncurrent
Consumers Energy Company
Operating leases
Right-of-use assets	$ 28	$ 40
Lease liabilities
Current lease liabilities	7	8
Noncurrent lease liabilities	21	32
Finance leases
Right-of-use assets	65	71
Lease liabilities
Finance lease liability	60
Current lease liabilities	7	6
Non-current lease liabilities	$ 53	$ 60
Weighted-average remaining lease term (in years)
Operating leases	18 years	14 years
Finance leases	12 years	12 years
Weighted-average discount rate
Operating leases	3.80%	3.70%
Finance leases	1.80%	1.90%
Related Party Lease
Lease liabilities
Finance lease liability	$ 25	$ 25
Current lease liabilities	$ 1	$ 1