Schedule II - Valuation and Qualifying Accounts and Reserves (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Allowance for uncollectible accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	$ 20	$ 24	$ 28
Charged to Other Accounts	0	0	0
Deductions	29	33	35
Balance at End of Period	20	20	24
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	24	28
Charged to Expense	29	29	31
Charged to Other Accounts	0	0	0
Deductions	29	33	35
Balance at End of Period	20	20	24
Deferred tax valuation allowance
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	15	5	4
Charged to Expense	2	10	1
Charged to Other Accounts	0	0	0
Deductions	9	0	0
Balance at End of Period	8	15	5
Allowance for notes receivable
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	20	16	9
Charged to Expense	25	20	19
Charged to Other Accounts	0	0	0
Deductions	21	16	12
Balance at End of Period	$ 24	$ 20	$ 16