Revenue (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) product	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Disaggregation of Revenue [Line Items]
Bad debt expense	$ 54	$ 49	$ 50
Unbilled receivables	$ 0	481
EnerBank
Disaggregation of Revenue [Line Items]
Threshold period past due when company ceases recognizing interest income	120 days
EnerBank | Consumer Loan
Disaggregation of Revenue [Line Items]
Number of products | product	4
EnerBank | Same As Cash Program
Disaggregation of Revenue [Line Items]
Description of timing of revenue recognition	EnerBank recognizes the fee on a straight-line basis over the same-as-cash period, which typically ranges from three to 24 months.
EnerBank | Zero Interest and Reduced Interest Programs
Disaggregation of Revenue [Line Items]
Description of timing of revenue recognition	EnerBank recognizes the fee using the interest method over the term of the loan, which ranges from one to 12 years.
Consumers Energy Company
Disaggregation of Revenue [Line Items]
Bad debt expense		29	$ 31
Unbilled receivables	$ 409	$ 481
Consumers Energy Company | Alternative Revenue Programs
Disaggregation of Revenue [Line Items]
Financial incentive as percentage of energy waste reduction program spending	20.00%
Accounts Receivable
Disaggregation of Revenue [Line Items]
Bad debt expense	$ 29
Accounts Receivable | Consumers Energy Company
Disaggregation of Revenue [Line Items]
Bad debt expense	$ 29