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Retirement Benefits | 6 Months Ended
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Jun. 30, 2021
Defined Benefit Plan Disclosure [Line Items] |
Retirement Benefits | Retirement BenefitsCMS Energy and Consumers provide pension, OPEB, and other retirement benefits to employees under a number of different plans. Costs: Presented in the following table are the costs (credits) and other changes in plan assets and benefit obligations incurred in CMS Energy’s and Consumers’ retirement benefits plans:
In Millions
| DB Pension Plans |  | OPEB Plan
| Three Months Ended |  | Six Months Ended |  | Three Months Ended |  | Six Months Ended
June 30 | 2021 | 2020 |  | 2021 | 2020 |  |  | 2021 | 2020 |  | 2021 | 2020 |
CMS Energy, including Consumers |  |
Net periodic cost (credit) |  |
Service cost |  | $ | 13 |  |  | $ | 13 |  |  |  | $ | 27 |  |  | $ | 25 |  |  |  |  |  | $ | 5 |  |  | $ | 4 |  |  |  | $ | 9 |  |  | $ | 8 |  |  |
Interest cost |  | 15 |  |  | 20 |  |  |  | 30 |  |  | 41 |  |  |  |  |  | 5 |  |  | 9 |  |  |  | 11 |  |  | 17 |  |  |
Expected return on plan assets |  | (52) |  |  | (48) |  |  |  | (104) |  |  | (96) |  |  |  |  |  | (27) |  |  | (25) |  |  |  | (54) |  |  | (50) |  |  |
Amortization of: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net loss |  | 26 |  |  | 22 |  |  |  | 51 |  |  | 44 |  |  |  |  |  | 2 |  |  | 3 |  |  |  | 4 |  |  | 7 |  |  |
Prior service cost (credit) |  | 1 |  |  | 1 |  |  |  | 2 |  |  | 1 |  |  |  |  |  | (13) |  |  | (14) |  |  |  | (26) |  |  | (28) |  |  |
Settlement loss |  | 2 |  |  | — |  |  |  | 3 |  |  | — |  |  |  |  |  | — |  |  | — |  |  |  | — |  |  | — |  |  |
Net periodic cost (credit) |  | $ | 5 |  |  | $ | 8 |  |  |  | $ | 9 |  |  | $ | 15 |  |  |  |  |  | $ | (28) |  |  | $ | (23) |  |  |  | $ | (56) |  |  | $ | (46) |  |  |
Consumers |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net periodic cost (credit) |  |
Service cost |  | $ | 13 |  |  | $ | 12 |  |  |  | $ | 26 |  |  | $ | 24 |  |  |  |  |  | $ | 5 |  |  | $ | 4 |  |  |  | $ | 9 |  |  | $ | 8 |  |  |
Interest cost |  | 14 |  |  | 19 |  |  |  | 28 |  |  | 39 |  |  |  |  |  | 5 |  |  | 8 |  |  |  | 11 |  |  | 16 |  |  |
Expected return on plan assets |  | (49) |  |  | (46) |  |  |  | (98) |  |  | (91) |  |  |  |  |  | (26) |  |  | (24) |  |  |  | (51) |  |  | (47) |  |  |
Amortization of: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net loss |  | 24 |  |  | 21 |  |  |  | 49 |  |  | 42 |  |  |  |  |  | 2 |  |  | 3 |  |  |  | 4 |  |  | 7 |  |  |
Prior service cost (credit) |  | 1 |  |  | 1 |  |  |  | 2 |  |  | 1 |  |  |  |  |  | (13) |  |  | (13) |  |  |  | (26) |  |  | (27) |  |  |
Settlement loss |  | 2 |  |  | — |  |  |  | 3 |  |  | — |  |  |  |  |  | — |  |  | — |  |  |  | — |  |  | — |  |  |
Net periodic cost (credit) |  | $ | 5 |  |  | $ | 7 |  |  |  | $ | 10 |  |  | $ | 15 |  |  |  |  |  | $ | (27) |  |  | $ | (22) |  |  |  | $ | (53) |  |  | $ | (43) |  |  |
Consumers Energy Company |
Defined Benefit Plan Disclosure [Line Items] |
Retirement Benefits | Retirement BenefitsCMS Energy and Consumers provide pension, OPEB, and other retirement benefits to employees under a number of different plans. Costs: Presented in the following table are the costs (credits) and other changes in plan assets and benefit obligations incurred in CMS Energy’s and Consumers’ retirement benefits plans:
In Millions
| DB Pension Plans |  | OPEB Plan
| Three Months Ended |  | Six Months Ended |  | Three Months Ended |  | Six Months Ended
June 30 | 2021 | 2020 |  | 2021 | 2020 |  |  | 2021 | 2020 |  | 2021 | 2020 |
CMS Energy, including Consumers |  |
Net periodic cost (credit) |  |
Service cost |  | $ | 13 |  |  | $ | 13 |  |  |  | $ | 27 |  |  | $ | 25 |  |  |  |  |  | $ | 5 |  |  | $ | 4 |  |  |  | $ | 9 |  |  | $ | 8 |  |  |
Interest cost |  | 15 |  |  | 20 |  |  |  | 30 |  |  | 41 |  |  |  |  |  | 5 |  |  | 9 |  |  |  | 11 |  |  | 17 |  |  |
Expected return on plan assets |  | (52) |  |  | (48) |  |  |  | (104) |  |  | (96) |  |  |  |  |  | (27) |  |  | (25) |  |  |  | (54) |  |  | (50) |  |  |
Amortization of: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net loss |  | 26 |  |  | 22 |  |  |  | 51 |  |  | 44 |  |  |  |  |  | 2 |  |  | 3 |  |  |  | 4 |  |  | 7 |  |  |
Prior service cost (credit) |  | 1 |  |  | 1 |  |  |  | 2 |  |  | 1 |  |  |  |  |  | (13) |  |  | (14) |  |  |  | (26) |  |  | (28) |  |  |
Settlement loss |  | 2 |  |  | — |  |  |  | 3 |  |  | — |  |  |  |  |  | — |  |  | — |  |  |  | — |  |  | — |  |  |
Net periodic cost (credit) |  | $ | 5 |  |  | $ | 8 |  |  |  | $ | 9 |  |  | $ | 15 |  |  |  |  |  | $ | (28) |  |  | $ | (23) |  |  |  | $ | (56) |  |  | $ | (46) |  |  |
Consumers |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net periodic cost (credit) |  |
Service cost |  | $ | 13 |  |  | $ | 12 |  |  |  | $ | 26 |  |  | $ | 24 |  |  |  |  |  | $ | 5 |  |  | $ | 4 |  |  |  | $ | 9 |  |  | $ | 8 |  |  |
Interest cost |  | 14 |  |  | 19 |  |  |  | 28 |  |  | 39 |  |  |  |  |  | 5 |  |  | 8 |  |  |  | 11 |  |  | 16 |  |  |
Expected return on plan assets |  | (49) |  |  | (46) |  |  |  | (98) |  |  | (91) |  |  |  |  |  | (26) |  |  | (24) |  |  |  | (51) |  |  | (47) |  |  |
Amortization of: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net loss |  | 24 |  |  | 21 |  |  |  | 49 |  |  | 42 |  |  |  |  |  | 2 |  |  | 3 |  |  |  | 4 |  |  | 7 |  |  |
Prior service cost (credit) |  | 1 |  |  | 1 |  |  |  | 2 |  |  | 1 |  |  |  |  |  | (13) |  |  | (13) |  |  |  | (26) |  |  | (27) |  |  |
Settlement loss |  | 2 |  |  | — |  |  |  | 3 |  |  | — |  |  |  |  |  | — |  |  | — |  |  |  | — |  |  | — |  |  |
Net periodic cost (credit) |  | $ | 5 |  |  | $ | 7 |  |  |  | $ | 10 |  |  | $ | 15 |  |  |  |  |  | $ | (27) |  |  | $ | (22) |  |  |  | $ | (53) |  |  | $ | (43) |  |  |

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