Notes Receivable (Narrative) (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
EnerBank
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes receivable	$ 2,231	$ 1,857
Unearned income	122	102
Delinquent loans	24	21
Consumers Energy Company
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes receivable	105	106
Current portion notes receivable related party	7	$ 7
Retail Installment Contracts | EnerBank
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes receivable	$ 238
CMS Energy Note Payable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest Rate	4.10%