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Retirement Benefits (Schedule Of Net Benefit Costs) (Details) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2019
Jun. 30, 2018
Jun. 30, 2019
Jun. 30, 2018
DB Pension Plans        
Net periodic cost (credit)        
Service cost $ 10 $ 12 $ 20 $ 24
Interest cost 24 23 49 45
Expected return on plan assets (41) (37) (81) (74)
Amortization of:        
Net loss 12 19 24 37
Prior service cost (credit) 1 0 1 1
Net periodic cost (credit) 6 17 13 33
DB Pension Plans | Consumers Energy Company        
Net periodic cost (credit)        
Service cost 10 11 20 23
Interest cost 23 21 46 42
Expected return on plan assets (38) (34) (76) (69)
Amortization of:        
Net loss 11 18 23 36
Prior service cost (credit) 1 0 1 1
Net periodic cost (credit) 7 16 14 33
OPEB Plan        
Net periodic cost (credit)        
Service cost 3 5 7 9
Interest cost 10 9 20 18
Expected return on plan assets (22) (25) (44) (49)
Amortization of:        
Net loss 6 4 13 8
Prior service cost (credit) (15) (17) (31) (34)
Net periodic cost (credit) (18) (24) (35) (48)
OPEB Plan | Consumers Energy Company        
Net periodic cost (credit)        
Service cost 4 4 7 8
Interest cost 10 9 20 17
Expected return on plan assets (20) (23) (41) (46)
Amortization of:        
Net loss 6 4 13 8
Prior service cost (credit) (16) (16) (31) (32)
Net periodic cost (credit) $ (16) $ (22) $ (32) $ (45)