Income Taxes (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2017	Dec. 31, 2018
Income Tax Benefits [Line Items]
Increase (decrease) to deferred income tax expense related to tax rate changes		$ 148,000,000
Alternative minimum tax, recovery period	4 years
Valuation allowance	$ 2,000,000		$ 8,000,000
Alternative minimum tax credit reclassification	31,000,000
Interest and penalties	0	0	0
Consumers Energy Company
Income Tax Benefits [Line Items]
Net regulatory tax liability	3,829,000,000		3,836,000,000
Increase (decrease) to deferred income tax expense related to tax rate changes		33,000,000
Interest and penalties	0	$ 0	$ 0
Local Tax Authority
Income Tax Benefits [Line Items]
Valuation allowance - loss carryforward	$ 2,000,000