Retirement Benefits (Schedule Of Net Periodic Benefit Cost Not yet Recognized) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Consumers Energy Company
Regulatory assets
Total regulatory assets	$ 2,695	$ 2,522
DB Pension Plans and DB SERP
Regulatory assets
Net loss	1,194	1,114
Prior service cost (credit)	29	8
Total regulatory assets	1,223	1,122
AOCI
Net loss (gain)	120	105
Prior service cost (credit)	1	0
Total amounts recognized in regulatory assets and AOCI	1,344	1,227
DB Pension Plans and DB SERP | Consumers Energy Company
Regulatory assets
Net loss	1,194	1,114
Prior service cost (credit)	29	8
Total regulatory assets	1,223	1,122
AOCI
Net loss (gain)	47	36
Total amounts recognized in regulatory assets and AOCI	1,270	1,158
OPEB Plan
Regulatory assets
Net loss	254	308
Prior service cost (credit)	(246)	(300)
Total regulatory assets	8	8
AOCI
Net loss (gain)	(10)	(6)
Prior service cost (credit)	(6)	(8)
Total amounts recognized in regulatory assets and AOCI	(8)	(6)
OPEB Plan | Consumers Energy Company
Regulatory assets
Net loss	254	308
Prior service cost (credit)	(246)	(300)
Total regulatory assets	8	8
AOCI
Net loss (gain)	0	0
Total amounts recognized in regulatory assets and AOCI	$ 8	$ 8