Retirement Benefits (Quarterly Narrative) (Details) - DB Pension Plans $ in Millions	6 Months Ended
	Jun. 30, 2022 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Settlement loss	$ 8
Increase (decrease) in non-current pension plan assets	113
Loss to AOCI	3
Consumers Energy Company
Defined Benefit Plan Disclosure [Line Items]
Increase (decrease) in non-current pension plan assets	110
Pension Costs
Defined Benefit Plan Disclosure [Line Items]
Settlement loss	8
Increase (decrease) in non-current pension plan assets	$ (110)
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	$ 8
Increase (decrease) in non-current pension plan assets	$ (110)