Leases and Palisades Financing - Assets and Liabilities of Lessee (Details) $ in Millions	Dec. 31, 2019 USD ($)
Operating leases
Right-of-use assets	$ 47
Lease liabilities
Current lease liabilities	9
Noncurrent lease liabilities	37
Finance lease liability	66
Finance leases
Right-of-use assets	71
Lease liabilities
Current lease liabilities	6
Non‑current lease liabilities	$ 60
Weighted-average remaining lease term (in years)
Operating leases	17 years
Finance leases	12 years
Weighted-average discount rate
Operating leases	3.80%
Finance leases	1.90%
Consumers Energy Company
Operating leases
Right-of-use assets	$ 40
Lease liabilities
Current lease liabilities	8
Noncurrent lease liabilities	32
Finance lease liability	66
Finance leases
Right-of-use assets	71
Lease liabilities
Current lease liabilities	6
Non‑current lease liabilities	$ 60
Weighted-average remaining lease term (in years)
Operating leases	14 years
Finance leases	12 years
Weighted-average discount rate
Operating leases	3.70%
Finance leases	1.90%
Related Party Lease
Lease liabilities
Finance lease liability	$ 25
Related Party Lease | Consumers Energy Company
Lease liabilities
Finance lease liability	25
Lease liabilities
Current lease liabilities	1
Maximum | Related Party Lease
Lease liabilities
Current lease liabilities	$ 1