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Schedule II - Valuation and Qualifying Accounts and Reserves (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Allowance for uncollectible accounts      
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]      
Balance at Beginning of Period $ 20 $ 20 $ 24
Charged to Expense 29 29 29
Charged to Other Accounts 0 0 0
Deductions 29 29 33
Balance at End of Period 20 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 24
Charged to Expense 29 29 29
Charged to Other Accounts 0 0 0
Deductions 29 29 33
Balance at End of Period 20 20 20
Deferred tax valuation allowance      
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]      
Balance at Beginning of Period 8 15 5
Charged to Expense 0 2 10
Charged to Other Accounts 0 0 0
Deductions 6 9 0
Balance at End of Period 2 8 15
Allowance for notes receivable      
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]      
Balance at Beginning of Period 24 20 16
Charged to Expense 38 25 20
Charged to Other Accounts 0 0 0
Deductions 29 21 16
Balance at End of Period $ 33 $ 24 $ 20