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Employee and Agent Benefits - Pension Plan Changes and Plan Gains/Losses (Details) - Pension benefits - USD ($) $ in Millions |  | 3 Months Ended | 6 Months Ended
--- | --- | --- | ---
May 31, 2019 | Jun. 30, 2020 | Jun. 30, 2020
Contributions |  |  |
Contributions made by employer to fund qualified and nonqualified pension plans |  | $ 15.7 | $ 21.4
Maximum |  |  |
Contributions |  |  |
Amount of possible contributions to be made during the current fiscal year to the qualified and nonqualified pension plans combined |  | $ 75.0 | $ 75.0
Nonqualified benefit plans |  |  |
Components of Net Periodic Benefit Cost (Income) |  |  |
Actuarial gain (loss) | $ (59.0) |  |
Total plan amendment gain | 122.4 |  |
Increase in benefit obligation | 237.6 |  |
Asset gain on plan assets | $ 178.6 |  |

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- Definition Amount of increase (decrease) in plan assets of defined benefit plan from actual return (loss) determined by change in fair value of plan assets adjusted for contributions, benefit payments, and other expenses. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=118257860&loc=d3e4179-114921 + Details
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- Definition Amount of gain (loss) from change in actuarial assumptions which (increases) decreases benefit obligation of defined benefit plan. Assumptions include, but are not limited to, interest, mortality, employee turnover, salary, and temporary deviation from substantive plan. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(4) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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