Retirement Benefits - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022 USD ($) employee	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Projected Retirement Benefit Expense In Next 12 months		$ 74.0
Defined Contribution Plan, Cost		$ 31.1	$ 20.4	$ 29.9
Termination benefits				17.4
Multiemployer Plans, Withdrawal Obligation, Payment Period		15 years
Income tax provision		$ 15.5	26.8	77.7
Settlement loss (gain) included in net income (loss)		29.5	(21.9)	0.0
Reclassification out of Accumulated Other Comprehensive Income [Member] | Post- retirement benefit plans [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Income tax provision		(12.0)	(11.9)	(19.7)
Settlement loss (gain) included in net income (loss)		29.5	(21.9)	0.0
Collective-Bargaining Arrangement, Other
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Income tax provision			15.5
Other Postretirement Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Curtailment loss (gain)		0.0	0.0	(0.2)
Employer contributions		0.0	0.0
Projected Retirement Benefit Expense In Next 12 months		16.0
Defined Contribution Plan, Cost		$ 1.0	$ 0.0	$ 0.7
Assumed increase in per capita cost of covered benefits in next 12 months		7.80%
Assumed ultimate health care cost trend rate		4.00%
Expected long-term rate of return on assets		0.00%	0.00%	0.00%
Fair value of plan assets		$ 0.0	$ 0.0	$ 0.0
Termination benefits		0.0	0.0	6.7
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Settlement		0.0	43.0
Settlement loss (gain) included in net income (loss)		0.0	(21.9)
Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Curtailment loss (gain)		0.0	0.0	$ 0.0
Employer contributions		57.4	77.3
Projected Retirement Benefit Expense In Next 12 months		58.0
Accumulated benefit obligation		$ 1,716.8	$ 2,398.0
Expected long-term rate of return on assets		6.43%	6.71%	7.16%
Actual return on plan assets		(14.50%)	12.40%	15.20%	15.10%	(4.80%)
Fair value of plan assets		$ 1,599.5	$ 2,120.9	$ 2,046.4
Defined Benefit Plan, Weighted Average Life Expectancy		17 years
Termination benefits		$ 0.0	0.0	10.9
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Settlement		0.0	0.0
Settlement loss (gain) included in net income (loss)		29.5	0.0
Pension Benefits [Member] | Global debt securities and cash [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Unfunded commitments		45.0
Pension Benefits [Member] | Private equity [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Unfunded commitments		125.0
Fair value of plan assets		224.3	176.7
Pension Benefits [Member] | Real estate and other [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Unfunded commitments		29.0
Pension Benefits [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		0.0	0.0
Pension Benefits [Member] | Fair Value, Inputs, Level 3 [Member] | Private equity [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		0.0	0.0
Pension Benefits [Member] | Forecast
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected long-term rate of return on assets	6.57%
Pension Benefits [Member] | MultiemployerPlan1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Multiemployer Plans, Withdrawal Obligation		27.0
Pension Benefits [Member] | Nonqualified plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Estimated employer contributions in next 12 months		$ 6.0
Pension Benefits [Member] | United States
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, number of employees accruing benefit service | employee		900
Defined Benefit Plan, Percent Of Employees accruing benefit service		7.00%
Percent reduction in defined benefit plan participation		60.00%
Employer contributions		$ 50.0	67.0	$ 130.0
Expected future voluntary contributions to pension plan		50.0
Estimated employer contributions in next 12 months		$ 0.0
Percentage of total assets		95.00%
Small annuity buy out [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Benefits paid			$ 70.0