Prior service cost

  
Components of net periodic benefit cost, recorded in underwriting, general and administrative expenses in the consolidated statements of operations, and other amounts recognized in AOCI for the years ended December 31, 2021, 2020, and 2019 were as follows: 

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|   | Pension Benefits |  | Retirement Health Benefits |
|   | 2021 |  | 2020 |  | 2019 |  | 2021 |  | 2020 |  | 2019 |
| Net periodic benefit cost |  |  |  |  |  |  |  |  |  |  |  |
| Interest cost | $ | 15.2  |  |  | $ | 22.4  |  |  | $ | 28.6  |  |  | $ | 0.1  |  |  | $ | 0.7  |  |  | $ | 3.1  |  |
| Expected return on plan assets | (27.3) |  |  | (30.6) |  |  | (35.5) |  |  | (1.5) |  |  | (1.8) |  |  | (1.9) |  |
| Amortization of prior service credit (cost) | 0.1  |  |  | 0.1  |  |  | —  |  |  | (13.6) |  |  | (11.3) |  |  | —  |  |
| Amortization of net loss (gain) | 7.8  |  |  | 5.1  |  |  | 1.2  |  |  | (0.6) |  |  | —  |  |  | (1.2) |  |
| Curtailment/settlement loss | 3.1  |  |  | 1.0  |  |  | 0.1  |  |  | —  |  |  | —  |  |  | —  |  |
| Net periodic benefit cost | $ | (1.1) |  |  | $ | (2.0) |  |  | $ | (5.6) |  |  | $ | (15.6) |  |  | $ | (12.4) |  |  | $ | —  |  |
| Other changes in plan assets and benefit obligations recognized in accumulated other comprehensive income |  |  |  |  |  |  |  |  |  |  |  |
| Prior service cost | $ | —  |  |  | —  |  |  | —  |  |  | $ | —  |  |  | (65.6) |  |  | —  |  |
| Net (gain) loss | (20.1) |  |  | 42.9  |  |  | 16.8  |  |  | (0.9) |  |  | 2.5  |  |  | (12.2) |  |
| Amortization of prior service (cost) credit | (0.1) |  |  | (0.1) |  |  | —  |  |  | 13.6  |  |  | 11.3  |  |  | —  |  |
| Amortization of net (loss) gain | (10.9) |  |  | (6.1) |  |  | (1.3) |  |  | 0.6  |  |  | —  |  |  | 1.2  |  |
| Total recognized in accumulated other comprehensive (loss) income | $ | (31.1) |  |  | $ | 36.7  |  |  | $ | 15.5  |  |  | $ | 13.3  |  |  | $ | (51.8) |  |  | $ | (11.0) |  |
| Total recognized in net periodic benefit cost and other comprehensive (loss) income | $ | (32.2) |  |  | $ | 34.7  |  |  | $ | 9.9  |  |  | $ | (2.3) |  |  | $ | (64.2) |  |  | $ | (11.0) |  |

  
The Company uses a five-year averaging method to determine the market-related value of Pension Benefits plan assets, which is used to calculate the expected return of plan assets component of the Plans’ expense. Under this methodology, asset gains/losses that result from actual returns which differ from the Company’s expected long-term rate of return on assets assumption are recognized in the market-related value of assets on a level basis over a five-year period. The difference between actual as compared to expected asset returns for the Plans will be fully reflected in the market-related value of plan assets over the next five years using the methodology described above. Other post-employment benefit assets under the Retirement Health Benefits are valued at fair value. Determination of the projected benefit obligation was based on the following weighted-average assumptions for the years ended December 31, 2021, 2020 and 2019: 

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|   | Qualified Pension Benefits |  | Unfunded Nonqualified Pension Benefits |  | Retirement Health Benefits |
|   | 2021 |  | 2020 |  | 2019 |  | 2021 |  | 2020 |  | 2019 |  | 2021 |  | 2020 |  | 2019 |
| Discount rate | 2.79  | % |  | 2.39  | % |  | 3.27  | % |  | 2.68  | % |  | 2.20  | % |  | 3.11  | % |  | 1.08  | % |  | 0.60  | % |  | 3.23  | % |

 Determination of the net periodic benefit cost was based on the following weighted-average assumptions for the years ended December 31, 2021, 2020 and 2019: 

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|   | Qualified Pension Benefits |  | Unfunded Nonqualified Pension Benefits |  | Retirement Health Benefits |
|   | 2021 |  | 2020 |  | 2019 |  | 2021 |  | 2020 |  | 2019 |  | 2021 |  | 2020 Pre-Amendment |  | 2020 Post-Amendment |  | 2019 |
| Discount rates: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
| Effective discount rate for benefit obligations | 2.39  | % |  | 3.27  | % |  | 4.33  | % |  | 2.20  | % |  | 3.11  | % |  | 4.21  | % |  | 0.60  | % |  | 3.23  | % |  | 1.55  | % |  | 4.30  | % |
| Effective rate for interest on benefit obligations | 1.80  | % |  | 2.84  | % |  | 3.98  | % |  | 1.45  | % |  | 2.77  | % |  | 3.88  | % |  | 0.55  | % |  | 2.83  | % |  | 1.53  | % |  | 3.99  | % |
| Expected long-term return on plan assets | 3.65  | % |  | 4.15  | % |  | 4.75  | % |  | —  | % |  | —  | % |  | —  | % |  | 3.65  | % |  | 4.15  | % |  | 4.15  | % |  | 4.75  | % |

 F-72
