Retirement Benefits (Quarterly Narrative) (Details) - DB Pension Plans $ in Millions	9 Months Ended
	Sep. 30, 2022 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Settlement loss	$ 19
Increase (decrease) in non-current pension plan assets	69
Gain to AOCI	2
Consumers Energy Company
Defined Benefit Plan Disclosure [Line Items]
Increase (decrease) in non-current pension plan assets	67
Pension Costs
Defined Benefit Plan Disclosure [Line Items]
Settlement loss	19
Increase (decrease) in non-current pension plan assets	$ (67)
Pension Costs | DB Pension Plan A Settlement
Defined Benefit Plan Disclosure [Line Items]
Regulatory asset collection period	8 years
Pension Costs | Consumers Energy Company
Defined Benefit Plan Disclosure [Line Items]
Settlement loss	$ 19
Increase (decrease) in non-current pension plan assets	$ (67)