Schedule II - Valuation and Qualifying Accounts and Reserves (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for Uncollectible Accounts [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	[1]	$ 24	$ 28	$ 40
Charged to Expense	[1]	29	31	50
Charged to other Accounts	[1]
Deductions	[1]	33	35	62
Balance at End of Period	[1]	20	24	28
Allowance for Uncollectible Accounts [Member] | Consumers Energy Company [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	[1]	24	28	39
Charged to Expense	[1]	29	31	50
Charged to other Accounts	[1]
Deductions	[1]	33	35	61
Balance at End of Period	[1]	20	24	28
Deferred Tax Valuation Allowance [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period		5	4	2
Charged to Expense		10	1	3
Charged to other Accounts				(1)
Deductions
Balance at End of Period		15	5	4
Deferred Tax Valuation Allowance [Member] | Consumers Energy Company [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period				1
Charged to Expense
Charged to other Accounts				(1)
Deductions
Balance at End of Period
Allowance For Notes Receivable [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	[1]	16	9	8
Charged to Expense	[1]	20	19	8
Charged to other Accounts	[1]
Deductions	[1]	16	12	7
Balance at End of Period	[1]	$ 20	$ 16	$ 9

[1] Deductions represent write-offs of uncollectible accounts, net of recoveries.