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Employee Benefit Plans: Plan Contributions (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2023 | Dec. 31, 2022
Defined Benefit Pension Plans |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Estimated Future Employer Contributions in Next Fiscal Year | $ 2.3 |
Payment for Pension Benefits | 0.0 | $ 0.0
Other Postretirement Benefits Plan |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Payment for Pension and Other Postretirement Benefits | 5.4 | 6.1
Payment for Pension Benefits | 4.3 | 4.5
Supplemental Non-Qualified Defined Benefit Plans |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Payment for Pension Benefits | 3.5 | 3.1
Defined Contribution Plan, Company Retirement |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Contribution Plan, Employer Discretionary Contribution Amount | 12.7 | 11.9
Defined Contribution Plan, 401K |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Contribution Plan, Employer Discretionary Contribution Amount | $ 17.1 | $ 16.2

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- Definition Amount of contribution expected to be received by defined benefit plan from employer in next fiscal year following current fiscal year. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 18 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480482/715-20-55-18 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (g) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 + Details
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