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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