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Retirement Benefits | 9 Months Ended
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Sep. 30, 2018
Defined Benefit Plan Disclosure [Line Items] |
Retirement Benefits | Retirement Benefits CMS Energy and Consumers provide pension, OPEB, and other retirement benefits to employees under a number of different plans. In November 2017, CMS Energy and Consumers approved certain amendments to the OPEB Plan, resulting in higher OPEB Plan credits in 2018 compared to 2017. 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 |  | Nine Months Ended |  | Three Months Ended |  | Nine Months Ended
September 30 | 2018 |  | 2017 |  |  | 2018 |  | 2017 |  |  | 2018 |  | 2017 |  |  | 2018 |  | 2017 |
CMS Energy, including Consumers
Net periodic cost (credit) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Service cost |  | $ | 12 |  |  | $ | 12 |  |  |  | $ | 36 |  |  | $ | 34 |  |  |  | $ | 4 |  |  | $ | 5 |  |  |  | $ | 13 |  |  | $ | 15 |
Interest cost |  | 22 |  |  | 23 |  |  |  | 67 |  |  | 67 |  |  |  | 9 |  |  | 13 |  |  |  | 27 |  |  | 39 |
Expected return on plan assets |  | (38 | ) |  | (39 | ) |  |  | (112 | ) |  | (115 | ) |  |  | (24 | ) |  | (22 | ) |  |  | (73 | ) |  | (67 | )
Amortization of: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net loss |  | 19 |  |  | 20 |  |  |  | 56 |  |  | 60 |  |  |  | 3 |  |  | 7 |  |  |  | 11 |  |  | 23 |
Prior service cost (credit) |  | 1 |  |  | 1 |  |  |  | 2 |  |  | 3 |  |  |  | (16 | ) |  | (8 | ) |  |  | (50 | ) |  | (26 | )
Net periodic cost (credit) |  | $ | 16 |  |  | $ | 17 |  |  |  | $ | 49 |  |  | $ | 49 |  |  |  | $ | (24 | ) |  | $ | (5 | ) |  |  | $ | (72 | ) |  | $ | (16 | )
Consumers
Net periodic cost (credit) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Service cost |  | $ | 12 |  |  | $ | 11 |  |  |  | $ | 35 |  |  | $ | 33 |  |  |  | $ | 4 |  |  | $ | 5 |  |  |  | $ | 12 |  |  | $ | 14 |
Interest cost |  | 22 |  |  | 22 |  |  |  | 64 |  |  | 65 |  |  |  | 8 |  |  | 12 |  |  |  | 25 |  |  | 38 |
Expected return on plan assets |  | (35 | ) |  | (38 | ) |  |  | (104 | ) |  | (112 | ) |  |  | (22 | ) |  | (21 | ) |  |  | (68 | ) |  | (63 | )
Amortization of: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net loss |  | 17 |  |  | 19 |  |  |  | 53 |  |  | 58 |  |  |  | 4 |  |  | 8 |  |  |  | 12 |  |  | 24 |
Prior service cost (credit) |  | 1 |  |  | 1 |  |  |  | 2 |  |  | 3 |  |  |  | (17 | ) |  | (8 | ) |  |  | (49 | ) |  | (25 | )
Net periodic cost (credit) |  | $ | 17 |  |  | $ | 15 |  |  |  | $ | 50 |  |  | $ | 47 |  |  |  | $ | (23 | ) |  | $ | (4 | ) |  |  | $ | (68 | ) |  | $ | (12 | )
Consumers Energy Company |
Defined Benefit Plan Disclosure [Line Items] |
Retirement Benefits | Retirement Benefits CMS Energy and Consumers provide pension, OPEB, and other retirement benefits to employees under a number of different plans. In November 2017, CMS Energy and Consumers approved certain amendments to the OPEB Plan, resulting in higher OPEB Plan credits in 2018 compared to 2017. 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 |  | Nine Months Ended |  | Three Months Ended |  | Nine Months Ended
September 30 | 2018 |  | 2017 |  |  | 2018 |  | 2017 |  |  | 2018 |  | 2017 |  |  | 2018 |  | 2017 |
CMS Energy, including Consumers
Net periodic cost (credit) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Service cost |  | $ | 12 |  |  | $ | 12 |  |  |  | $ | 36 |  |  | $ | 34 |  |  |  | $ | 4 |  |  | $ | 5 |  |  |  | $ | 13 |  |  | $ | 15 |
Interest cost |  | 22 |  |  | 23 |  |  |  | 67 |  |  | 67 |  |  |  | 9 |  |  | 13 |  |  |  | 27 |  |  | 39 |
Expected return on plan assets |  | (38 | ) |  | (39 | ) |  |  | (112 | ) |  | (115 | ) |  |  | (24 | ) |  | (22 | ) |  |  | (73 | ) |  | (67 | )
Amortization of: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net loss |  | 19 |  |  | 20 |  |  |  | 56 |  |  | 60 |  |  |  | 3 |  |  | 7 |  |  |  | 11 |  |  | 23 |
Prior service cost (credit) |  | 1 |  |  | 1 |  |  |  | 2 |  |  | 3 |  |  |  | (16 | ) |  | (8 | ) |  |  | (50 | ) |  | (26 | )
Net periodic cost (credit) |  | $ | 16 |  |  | $ | 17 |  |  |  | $ | 49 |  |  | $ | 49 |  |  |  | $ | (24 | ) |  | $ | (5 | ) |  |  | $ | (72 | ) |  | $ | (16 | )
Consumers
Net periodic cost (credit) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Service cost |  | $ | 12 |  |  | $ | 11 |  |  |  | $ | 35 |  |  | $ | 33 |  |  |  | $ | 4 |  |  | $ | 5 |  |  |  | $ | 12 |  |  | $ | 14 |
Interest cost |  | 22 |  |  | 22 |  |  |  | 64 |  |  | 65 |  |  |  | 8 |  |  | 12 |  |  |  | 25 |  |  | 38 |
Expected return on plan assets |  | (35 | ) |  | (38 | ) |  |  | (104 | ) |  | (112 | ) |  |  | (22 | ) |  | (21 | ) |  |  | (68 | ) |  | (63 | )
Amortization of: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net loss |  | 17 |  |  | 19 |  |  |  | 53 |  |  | 58 |  |  |  | 4 |  |  | 8 |  |  |  | 12 |  |  | 24 |
Prior service cost (credit) |  | 1 |  |  | 1 |  |  |  | 2 |  |  | 3 |  |  |  | (17 | ) |  | (8 | ) |  |  | (49 | ) |  | (25 | )
Net periodic cost (credit) |  | $ | 17 |  |  | $ | 15 |  |  |  | $ | 50 |  |  | $ | 47 |  |  |  | $ | (23 | ) |  | $ | (4 | ) |  |  | $ | (68 | ) |  | $ | (12 | )

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition The entire disclosure for pension and other postretirement benefits. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -URI http://asc.fasb.org/topic&trid=2235017 + Details
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