Fair Value Measurements (Narrative) (Details) - Consumers Energy Company $ in Millions		12 Months Ended
	Dec. 31, 2021 USD ($)	Dec. 31, 2021 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fleet assets held for sale	$ 19	$ 19
Electric Rate Case
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Plant retirements, impact of disallowances and transfers to held for sale	15
Impairment charge	$ 4	$ 45