Retirement Benefits (Schedule Of Net Periodic Benefit Cost Not yet Recognized) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Consumers Energy Company
Regulatory assets
Total regulatory assets	$ 2,522	$ 1,780
DB Pension Plans and DB SERP
Regulatory assets
Net loss	1,114	978
Prior service cost (credit)	8	9
Total regulatory assets	1,122	987
AOCI
Net loss (gain)	105	90
Prior service credit	0	0
Total amounts recognized in regulatory assets and AOCI	1,227	1,077
DB Pension Plans and DB SERP | Consumers Energy Company
Regulatory assets
Net loss	1,114	978
Prior service cost (credit)	8	9
Total regulatory assets	1,122	987
AOCI
Net loss (gain)	36	27
Total amounts recognized in regulatory assets and AOCI	1,158	1,014
OPEB Plan
Regulatory assets
Net loss	308	402
Prior service cost (credit)	(300)	(361)
Total regulatory assets	8	41
AOCI
Net loss (gain)	(6)	2
Prior service credit	(8)	(9)
Total amounts recognized in regulatory assets and AOCI	(6)	34
OPEB Plan | Consumers Energy Company
Regulatory assets
Net loss	308	402
Prior service cost (credit)	(300)	(361)
Total regulatory assets	8	41
AOCI
Net loss (gain)	0	0
Total amounts recognized in regulatory assets and AOCI	$ 8	$ 41