Retirement Benefits (Quarterly Narrative) (Details) - DB Pension Plans - USD ($) $ in Millions		3 Months Ended
	Mar. 31, 2022	Mar. 31, 2022
Defined Benefit Plan Disclosure [Line Items]
Settlement loss	$ 4
Increase (decrease) in non-current pension plan assets		$ 91
Loss to AOCI		2
Consumers Energy Company
Defined Benefit Plan Disclosure [Line Items]
Increase (decrease) in non-current pension plan assets		$ 89
Pension Costs
Defined Benefit Plan Disclosure [Line Items]
Settlement loss	4
Increase (decrease) in non-current pension plan assets	(89)
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	4
Increase (decrease) in non-current pension plan assets	$ (89)