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Retirement Benefits (Schedule Of Benefit Obligations In Excess Of Fair Value Of Plan Assets) (Details) - USD ($)
$ in Millions
1 Months Ended 12 Months Ended
Jul. 31, 2018
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
DB Pension Plans        
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]        
Benefit obligation at beginning of period   $ 2,512 $ 2,780  
Service cost   41 48  
Interest cost   98 90  
Plan amendments   0 0  
Actuarial loss (gain)   476 (258)  
Benefits paid   (154) (148)  
Benefit obligation at end of period   2,973 2,512 $ 2,780
Defined Benefit Plan, Roll Forwards [Abstract]        
Plan assets at fair value at beginning of period   2,247 2,305  
Actual return on plan assets   453 (150)  
Company contribution   0 240  
Actual benefits paid   (154) (148)  
Plan assets at fair value at end of period   2,546 2,247 2,305
Funded status   (427) (265)  
DB Pension Plans | Consumers Energy Company        
Defined Benefit Plan, Roll Forwards [Abstract]        
Funded status   (408) (246)  
DB SERP        
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]        
Benefit obligation at beginning of period   140 154  
Service cost   0 0  
Interest cost   5 5  
Plan amendments   0 0  
Actuarial loss (gain)   15 (10)  
Benefits paid   (10) (9)  
Benefit obligation at end of period   150 140 154
Defined Benefit Plan, Roll Forwards [Abstract]        
Plan assets at fair value at beginning of period   0 0  
Actual return on plan assets   0 0  
Company contribution   10 9  
Actual benefits paid   (10) (9)  
Plan assets at fair value at end of period   0 0 0
Funded status   (150) (140)  
DB SERP | Consumers Energy Company        
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]        
Benefit obligation at beginning of period   101 112  
Service cost   0 0  
Interest cost   4 4  
Plan amendments   0 0  
Actuarial loss (gain)   11 (8)  
Benefits paid   (7) (7)  
Benefit obligation at end of period   109 101 112
Defined Benefit Plan, Roll Forwards [Abstract]        
Plan assets at fair value at beginning of period   0 0  
Actual return on plan assets   0 0  
Company contribution   7 7  
Actual benefits paid   (7) (7)  
Plan assets at fair value at end of period   0 0 0
Funded status   (109) (101)  
OPEB Plan        
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]        
Benefit obligation at beginning of period   1,045 1,097  
Service cost   14 17 19
Interest cost   41 34 51
Plan amendments $ 26 0    
Actuarial loss (gain)   110 (74)  
Benefits paid   (45) (55)  
Benefit obligation at end of period   1,165 1,045 1,097
Defined Benefit Plan, Roll Forwards [Abstract]        
Plan assets at fair value at beginning of period   1,280 1,420  
Actual return on plan assets   273 (86)  
Company contribution   0 0  
Actual benefits paid   (44) (54)  
Plan assets at fair value at end of period   1,509 1,280 1,420
Funded status   344 235  
OPEB Plan | Consumers Energy Company        
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]        
Benefit obligation at beginning of period   1,004 1,053  
Service cost   13 16 19
Interest cost   40 33 49
Plan amendments   0 25  
Actuarial loss (gain)   106 (70)  
Benefits paid   (43) (53)  
Benefit obligation at end of period   1,120 1,004 1,053
Defined Benefit Plan, Roll Forwards [Abstract]        
Plan assets at fair value at beginning of period   1,197 1,329  
Actual return on plan assets   255 (80)  
Company contribution   0 0  
Actual benefits paid   (42) (52)  
Plan assets at fair value at end of period   1,410 1,197 $ 1,329
Funded status   $ 290 $ 193