Retirement Benefits (Schedule Of SERP Trust Assets, ABO And Contributions) (Details) - DB SERP - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Trust assets	$ 0	$ 0	$ 0
ABO	149	137
Contributions	0	8
Consumers Energy Company
Defined Benefit Plan Disclosure [Line Items]
Trust assets	0	0	$ 0
ABO	107	98
Contributions	0	5
Trust assets
Defined Benefit Plan Disclosure [Line Items]
Trust assets	143	147
Trust assets | Consumers Energy Company
Defined Benefit Plan Disclosure [Line Items]
Trust assets	$ 104	$ 106