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Retirement Benefits (Schedule of Net Benefit Costs) (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2025 | Sep. 30, 2024
DB Pension Plans |  |  |  |
Defined Benefit Plan, Roll Forwards [Abstract] |  |  |  |
Service cost | $ 6 | $ 7 | $ 19 | $ 21
Interest cost | 27 | 26 | 81 | 78
Expected return on plan assets | (57) | (58) | (171) | (176)
Amortization of: |  |  |  |
Net loss | 3 | 3 | 8 | 9
Prior service cost (credit) | 1 | 1 | 3 | 3
Settlement loss | 3 | 3 | 8 | 8
Net periodic credit | (17) | (18) | (52) | (57)
DB Pension Plans | Consumers Energy Company |  |  |  |
Defined Benefit Plan, Roll Forwards [Abstract] |  |  |  |
Service cost | 6 | 7 | 18 | 20
Interest cost | 26 | 25 | 77 | 74
Expected return on plan assets | (54) | (56) | (162) | (166)
Amortization of: |  |  |  |
Net loss | 2 | 3 | 7 | 8
Prior service cost (credit) | 1 | 1 | 3 | 3
Settlement loss | 3 | 3 | 8 | 8
Net periodic credit | (16) | (17) | (49) | (53)
OPEB Plan |  |  |  |
Defined Benefit Plan, Roll Forwards [Abstract] |  |  |  |
Service cost | 2 | 2 | 6 | 8
Interest cost | 10 | 10 | 32 | 32
Expected return on plan assets | (27) | (28) | (83) | (86)
Amortization of: |  |  |  |
Net loss | 0 | 1 | 2 | 3
Prior service cost (credit) | (8) | (7) | (25) | (23)
Settlement loss | 0 | 0 | 0 | 0
Net periodic credit | (23) | (22) | (68) | (66)
OPEB Plan | Consumers Energy Company |  |  |  |
Defined Benefit Plan, Roll Forwards [Abstract] |  |  |  |
Service cost | 2 | 2 | 6 | 8
Interest cost | 11 | 11 | 32 | 31
Expected return on plan assets | (26) | (26) | (78) | (80)
Amortization of: |  |  |  |
Net loss | 0 | 1 | 2 | 3
Prior service cost (credit) | (8) | (8) | (25) | (23)
Settlement loss | 0 | 0 | 0 | 0
Net periodic credit | $ (21) | $ (20) | $ (63) | $ (61)

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