Pension Plans - Qualified and Non-Qualified Plans - Amounts Recognized in Other Comprehensive Income (Details) - Pension Plan [Member] - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), after Reclassification Adjustment, before Tax [Abstract]
Net gain (loss) recognized in other comprehensive income	$ 5.3	$ (0.6)	$ 9.9
Net gain (loss) recognized in other comprehensive income after tax	(1.6)	0.0	$ 0.0
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax [Abstract]
Unrecognized actuarial losses included in other comprehensive loss, net of tax	16.3	20.0
Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, before Tax [Abstract]
Unrecognized actuarial losses included in other comprehensive loss	$ 21.5	$ 26.7

Amount, after tax, of accumulated other comprehensive (income) loss for defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

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