Pension and Savings Plans - Changes in the Fair Value of Master Trust's Level 3 Investments (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Fair value of plan assets at beginning of period	$ 430.4	$ 0.3	$ 1.2
Realized (losses) gains	(10.4)	0.1	0.9
Unrealized losses relating to investments still held at the reporting date	0.0	(68.8)	(0.6)
Purchases, sales and settlements, net	(420.0)	498.8	(1.2)
Fair value of plan assets at end of period	0.0	430.4	0.3
Pension Plan
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Fair value of plan assets at beginning of period	583.3	772.4
Fair value of plan assets at end of period	116.0	583.3	$ 772.4
Pension Plan \| Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Fair value of plan assets at beginning of period	430.4
Fair value of plan assets at end of period	0.0	430.4
Pension Plan \| Level 3 \| Real estate interests
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Fair value of plan assets at beginning of period	$ 0.3
Fair value of plan assets at end of period		$ 0.3

Defined benefit plan actual return on plan assets unrealized during period.

No definition available.

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- Definition

Amount, measured using unobservable inputs, of increase (decrease) in plan assets of defined benefit plan from actual return (loss) on assets still held.

+ References

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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- Definition

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.

+ References

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- Definition

Amount, measured using unobservable input, of increase (decrease) in plan asset of defined benefit plan from purchase, sale and settlement of trade associated with underlying investment.

+ References

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