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Employee Benefit Plans: Fair Value Measurements (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Pension Plan
Defined Benefit Plan, Plan Assets, Amount	$ 270.2	$ 308.6	$ 323.1
Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	270.2	308.4
Defined Benefit Plan, Fair Value of Plan Assets, Excluding Net Asset Value investments	247.7	283.9
Defined Benefit Plan, Alternative Investments, Fair Value Of Plan Assets	22.5	24.5
Fair Value, Measurements, Recurring | Healthcare Plan
Defined Benefit Plan, Plan Assets, Amount	7.5	8.0
Defined Benefit Plan, Fair Value of Plan Assets, Excluding Net Asset Value investments	7.5	8.0
Defined Benefit Plan, Alternative Investments, Fair Value Of Plan Assets	0.0	0.0
Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	0.0	0.0
Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring | Healthcare Plan
Defined Benefit Plan, Plan Assets, Amount	7.5	8.0
Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	247.7	283.9
Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring | Healthcare Plan
Defined Benefit Plan, Plan Assets, Amount	0.0	0.0
Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	0.0	0.0
Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring | Healthcare Plan
Defined Benefit Plan, Plan Assets, Amount	$ 0.0	0.0
Common Collective Trust Funds | Minimum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period	15 days
Common Collective Trust, Cash And Cash Equivalents | Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	$ 5.4	6.7
Defined Benefit Plan, Fair Value of Plan Assets, Excluding Net Asset Value investments	5.4	6.7
Defined Benefit Plan, Alternative Investments, Fair Value Of Plan Assets	0.0	0.0
Common Collective Trust, Cash And Cash Equivalents | Fair Value, Measurements, Recurring | Healthcare Plan
Defined Benefit Plan, Alternative Investments, Fair Value Of Plan Assets	0.0	0.0
Common Collective Trust, Cash And Cash Equivalents | Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	0.0	0.0
Common Collective Trust, Cash And Cash Equivalents | Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	5.4	6.7
Common Collective Trust, Cash And Cash Equivalents | Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	0.0	0.0
Common Collective Trust - Equity | Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	51.5	42.7
Defined Benefit Plan, Fair Value of Plan Assets, Excluding Net Asset Value investments	51.5	42.7
Defined Benefit Plan, Alternative Investments, Fair Value Of Plan Assets	0.0	0.0
Common Collective Trust - Equity | Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	0.0	0.0
Common Collective Trust - Equity | Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	51.5	42.7
Common Collective Trust - Equity | Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	0.0	0.0
Common Collective Trust - Fixed Income | Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	190.8	234.5
Defined Benefit Plan, Fair Value of Plan Assets, Excluding Net Asset Value investments	190.8	234.5
Defined Benefit Plan, Alternative Investments, Fair Value Of Plan Assets	0.0	0.0
Common Collective Trust - Fixed Income | Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	0.0	0.0
Common Collective Trust - Fixed Income | Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	190.8	234.5
Common Collective Trust - Fixed Income | Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	$ 0.0	0.0
Common Collective Trust - Real Estate | Minimum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period	105 days
Common Collective Trust - Real Estate | Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	$ 14.9	16.4
Defined Benefit Plan, Fair Value of Plan Assets, Excluding Net Asset Value investments	0.0	0.0
Defined Benefit Plan, Alternative Investments, Fair Value Of Plan Assets	14.9	16.4
Common Collective Trust - Real Estate | Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	0.0	0.0
Common Collective Trust - Real Estate | Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	0.0	0.0
Common Collective Trust - Real Estate | Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	$ 0.0	0.0
Hedge Funds | Minimum
Percentage Of Monthly Redemption	10.00%
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period	15 days
Hedge Funds | Maximum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period	60 days
Hedge Funds | Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	$ 7.6	8.1
Defined Benefit Plan, Fair Value of Plan Assets, Excluding Net Asset Value investments	0.0	0.0
Defined Benefit Plan, Alternative Investments, Fair Value Of Plan Assets	7.6	8.1
Hedge Funds | Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	0.0	0.0
Hedge Funds | Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	0.0	0.0
Hedge Funds | Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	0.0	0.0
Cash | Fair Value, Measurements, Recurring | Healthcare Plan
Defined Benefit Plan, Plan Assets, Amount	7.5	8.0
Defined Benefit Plan, Fair Value of Plan Assets, Excluding Net Asset Value investments	7.5	8.0
Cash | Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring | Healthcare Plan
Defined Benefit Plan, Plan Assets, Amount	7.5	8.0
Cash | Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring | Healthcare Plan
Defined Benefit Plan, Plan Assets, Amount	0.0	0.0
Cash | Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring | Healthcare Plan
Defined Benefit Plan, Plan Assets, Amount	$ 0.0	$ 0.0

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Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee.

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