Plant, Property, and Equipment (Schedule of Finance Leases and Other Financing Obligations) (Details) - Consumers Energy Company - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Finance Leases and Other Financing Obligations, Rollforward [Roll Forward]
Balance at beginning of period	$ 340	$ 309
Additions	0	26
Net retirements and other adjustments	(4)	5
Balance at end of period	336	340
Finance lease accumulated amortization	$ 254	$ 239