Schedule II - Valuation and Qualifying Accounts and Reserves (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Allowance for uncollectible accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	$ 20	$ 20	$ 20
Charged to Expense	33	29	29
Charged to Other Accounts	0	0	0
Deductions	24	29	29
Balance at End of Period	29	20	20
Allowance for uncollectible accounts | Consumers Energy Company
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	20	20	20
Charged to Expense	33	29	29
Charged to Other Accounts	0	0	0
Deductions	24	29	29
Balance at End of Period	29	20	20
Deferred tax valuation allowance
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	2	8	15
Charged to Expense	0	0	2
Charged to Other Accounts	0	0	0
Deductions	1	6	9
Balance at End of Period	1	2	8
Allowance for notes receivable
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	33	24	20
Charged to Expense	60	38	25
Charged to Other Accounts	62	0	0
Deductions	32	29	21
Balance at End of Period	$ 123	$ 33	$ 24