Schedule II - Valuation and Qualifying Accounts and Reserves (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Allowance for Uncollectible Accounts [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	[1]	$ 40	$ 33	$ 32
Charged to Expense	[1]	$ 50	$ 72	$ 63
Charged to other Accounts	[1]
Deductions	[1]	$ 62	$ 65	$ 62
Balance at End of Period	[1]	28	40	33
Allowance for Uncollectible Accounts [Member] | Consumers Energy Company [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period		39	31	30
Charged to Expense		$ 50	$ 72	$ 63
Charged to other Accounts
Deductions		$ 61	$ 64	$ 62
Balance at End of Period		28	39	31
Deferred Tax Valuation Allowance [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period		2	$ 2	$ 3
Charged to Expense		3
Charged to other Accounts		(1)
Deductions				$ 1
Balance at End of Period		4	$ 2	2
Deferred Tax Valuation Allowance [Member] | Consumers Energy Company [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period		$ 1	$ 1	$ 1
Charged to Expense
Charged to other Accounts		$ (1)
Deductions
Balance at End of Period			$ 1	$ 1
Allowance For Notes Receivable [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	[1]	$ 8	5	5
Charged to Expense	[1]	$ 8	$ 8	$ 4
Charged to other Accounts	[1]
Deductions	[1]	$ 7	$ 5	$ 4
Balance at End of Period	[1]	$ 9	$ 8	$ 5

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