Leases - Minimum Annual Rental Commitments post Topic 842 (Details) $ in Millions	Mar. 31, 2019 USD ($)
Operating Leases
Remainder of 2019	$ 8
2020	11
2021	11
2022	5
2023	3
2024	2
2025 and thereafter	35
Total minimum lease payments	75
Less discount	21
Present value of minimum lease payments	54
Finance Leases
Remainder of 2019	19
2020	23
2021	23
2022	19
2023	19
2024	16
2025 and thereafter	90
Total minimum lease payments	209
Less discount	136
Present value of minimum lease payments	73
Consumers Energy Company
Operating Leases
Remainder of 2019	7
2020	10
2021	9
2022	4
2023	2
2024	1
2025 and thereafter	29
Total minimum lease payments	62
Less discount	17
Present value of minimum lease payments	45
Finance Leases
Remainder of 2019	19
2020	23
2021	23
2022	19
2023	19
2024	16
2025 and thereafter	90
Total minimum lease payments	209
Less discount	136
Present value of minimum lease payments	73
Railcars
Operating Leases
Remainder of 2019	5
2020	7
2021	7
2022	2
2023	1
2024	0
2025 and thereafter	0
Total minimum lease payments	22
Less discount	1
Present value of minimum lease payments	21
Railcars | Consumers Energy Company
Operating Leases
Remainder of 2019	5
2020	7
2021	7
2022	2
2023	1
2024	0
2025 and thereafter	0
Total minimum lease payments	22
Less discount	1
Present value of minimum lease payments	21
Real Estate
Operating Leases
Remainder of 2019	2
2020	3
2021	3
2022	2
2023	2
2024	2
2025 and thereafter	34
Total minimum lease payments	48
Less discount	20
Present value of minimum lease payments	28
Finance Leases
Remainder of 2019	0
2020	0
2021	0
2022	0
2023	0
2024	0
2025 and thereafter	10
Total minimum lease payments	10
Less discount	2
Present value of minimum lease payments	8
Real Estate | Consumers Energy Company
Operating Leases
Remainder of 2019	1
2020	2
2021	1
2022	1
2023	1
2024	1
2025 and thereafter	28
Total minimum lease payments	35
Less discount	16
Present value of minimum lease payments	19
Finance Leases
Remainder of 2019	0
2020	0
2021	0
2022	0
2023	0
2024	0
2025 and thereafter	10
Total minimum lease payments	10
Less discount	2
Present value of minimum lease payments	8
PPAs
Operating Leases
Remainder of 2019	1
2020	1
2021	1
2022	1
2023	0
2024	0
2025 and thereafter	1
Total minimum lease payments	5
Less discount	0
Present value of minimum lease payments	5
Finance Leases
Remainder of 2019	10
2020	13
2021	13
2022	13
2023	13
2024	13
2025 and thereafter	74
Total minimum lease payments	149
Less discount	121
Present value of minimum lease payments	28
PPAs | Consumers Energy Company
Operating Leases
Remainder of 2019	1
2020	1
2021	1
2022	1
2023	0
2024	0
2025 and thereafter	1
Total minimum lease payments	5
Less discount	0
Present value of minimum lease payments	5
Finance Leases
Remainder of 2019	10
2020	13
2021	13
2022	13
2023	13
2024	13
2025 and thereafter	74
Total minimum lease payments	149
Less discount	121
Present value of minimum lease payments	28
Service Vehicles
Finance Leases
Remainder of 2019	6
2020	6
2021	5
2022	5
2023	5
2024	2
2025 and thereafter	3
Total minimum lease payments	32
Less discount	2
Present value of minimum lease payments	30
Service Vehicles | Consumers Energy Company
Finance Leases
Remainder of 2019	6
2020	6
2021	5
2022	5
2023	5
2024	2
2025 and thereafter	3
Total minimum lease payments	32
Less discount	2
Present value of minimum lease payments	30
Gas Pipelines
Finance Leases
Remainder of 2019	3
2020	4
2021	5
2022	1
2023	1
2024	1
2025 and thereafter	3
Total minimum lease payments	18
Less discount	11
Present value of minimum lease payments	7
Gas Pipelines | Consumers Energy Company
Finance Leases
Remainder of 2019	3
2020	4
2021	5
2022	1
2023	1
2024	1
2025 and thereafter	3
Total minimum lease payments	18
Less discount	11
Present value of minimum lease payments	$ 7