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Retirement Benefits (Schedule of Net Benefit Costs) (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2024 | Jun. 30, 2023 | Jun. 30, 2024 | Jun. 30, 2023
DB Pension Plans |  |  |  |
Defined Benefit Plan, Roll Forwards [Abstract] |  |  |  |
Service cost | $ 7 | $ 8 | $ 14 | $ 15
Interest cost | 26 | 26 | 52 | 53
Expected return on plan assets | (59) | (55) | (118) | (110)
Amortization of: |  |  |  |
Net loss | 3 | 3 | 6 | 6
Prior service cost (credit) | 1 | 1 | 2 | 2
Settlement loss | 2 | 3 | 5 | 5
Net periodic credit | (20) | (14) | (39) | (29)
DB Pension Plans | Volatility Mechanism |  |  |  |
Amortization of: |  |  |  |
Deferred credits |  |  | 9 |
DB Pension Plans | Consumers Energy Company |  |  |  |
Defined Benefit Plan, Roll Forwards [Abstract] |  |  |  |
Service cost | 6 | 7 | 13 | 14
Interest cost | 25 | 26 | 49 | 51
Expected return on plan assets | (55) | (52) | (110) | (104)
Amortization of: |  |  |  |
Net loss | 2 | 2 | 5 | 5
Prior service cost (credit) | 1 | 1 | 2 | 2
Settlement loss | 2 | 3 | 5 | 5
Net periodic credit | (19) | (13) | (36) | (27)
OPEB Plan |  |  |  |
Defined Benefit Plan, Roll Forwards [Abstract] |  |  |  |
Service cost | 3 | 3 | 6 | 6
Interest cost | 11 | 11 | 22 | 22
Expected return on plan assets | (29) | (25) | (58) | (51)
Amortization of: |  |  |  |
Net loss | 1 | 3 | 2 | 6
Prior service cost (credit) | (8) | (11) | (16) | (21)
Settlement loss | 0 | 0 | 0 | 0
Net periodic credit | (22) | (19) | (44) | (38)
OPEB Plan | Volatility Mechanism |  |  |  |
Amortization of: |  |  |  |
Deferred credits |  |  | 4 |
OPEB Plan | Consumers Energy Company |  |  |  |
Defined Benefit Plan, Roll Forwards [Abstract] |  |  |  |
Service cost | 3 | 3 | 6 | 6
Interest cost | 10 | 10 | 20 | 21
Expected return on plan assets | (27) | (24) | (54) | (48)
Amortization of: |  |  |  |
Net loss | 1 | 3 | 2 | 6
Prior service cost (credit) | (8) | (10) | (15) | (20)
Settlement loss | 0 | 0 | 0 | 0
Net periodic credit | $ (21) | $ (18) | $ (41) | $ (35)

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