Retirement Benefits - Narrative (Details) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2020 USD ($) employee	Dec. 31, 2021	Dec. 31, 2020 USD ($) employee	Dec. 31, 2019 USD ($) employee	Dec. 31, 2018 USD ($)	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined contribution plan, deferred contributions due to COVID-19 pandemic	$ 7.3		$ 7.3
Projected Retirement Benefit Expense In Next 12 months			44.0
Defined Contribution Plan, Cost			29.9	$ 44.8	$ 39.9
Termination benefits	17.4		$ 17.4
Multiemployer Plans, Withdrawal Obligation, Payment Period			20 years
UNITED KINGDOM
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Plan assets pledged as collateral	$ 62.0		$ 62.0
Other Postretirement Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate			3.25%	4.35%	3.80%
Curtailment loss (gain)			$ 0.2	$ 0.0	$ 0.0
Employer contributions			0.0	0.0
Projected Retirement Benefit Expense In Next 12 months			21.0
Defined Contribution Plan, Cost			$ 0.7	$ 1.0	$ 1.0
Assumed increase in per capita cost of covered benefits in next 12 months	5.60%		5.60%
Assumed ultimate health care cost trend rate	4.50%		4.50%
Expected long-term rate of return on assets			0.00%	4.00%	4.00%
Fair value of plan assets	$ 0.0		$ 0.0	$ 0.1	$ 0.1
Termination benefits			$ 6.7	$ 0.0	$ 0.0
Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate			3.40%	4.40%	3.85%
Curtailment loss (gain)			$ 0.0	$ 0.0	$ (0.4)
Employer contributions			138.8	153.4
Projected Retirement Benefit Expense In Next 12 months			23.0
Accumulated benefit obligation	2,703.9		$ 2,703.9	$ 2,621.1
Expected long-term rate of return on assets			7.16%	7.52%	7.75%
Actual return on plan assets			15.20%	15.10%	(4.80%)	16.90%	5.30%
Fair value of plan assets	2,046.4		$ 2,046.4	$ 1,902.1	$ 1,772.2
Defined Benefit Plan, Weighted Average Life Expectancy			18 years
Termination benefits			$ 10.9	0.0	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	78.0		78.0
Pension Benefits [Member] | Private equity [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Unfunded commitments	94.0		94.0
Fair value of plan assets	130.0		130.0	129.0
Pension Benefits [Member] | Hedge funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	325.0		325.0	263.9
Pension Benefits [Member] | Real estate and other [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Unfunded commitments	8.0		8.0
Fair value of plan assets	26.9		26.9	37.8
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	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	0.0
Pension Benefits [Member] | Fair Value, Inputs, Level 3 [Member] | Hedge funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0.0		0.0	0.0
Pension Benefits [Member] | Fair Value, Inputs, Level 3 [Member] | Real estate and other [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0.0		0.0	$ 0.0
Pension Benefits [Member] | Forecast [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected long-term rate of return on assets		6.78%
Pension Benefits [Member] | MultiemployerPlan1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Percent of Current Year Contributions to Plan that Company Contributions Exceed				5.00%
Multiemployer Plans, Withdrawal Obligation	38.0		38.0
Pension Benefits [Member] | Nonqualified and U.K. [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Estimated employer contributions in next 12 months	$ 10.0		$ 10.0
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	1,300		1,300
Defined Benefit Plan, Percent Of Employees accruing benefit service	10.00%		10.00%
Employer contributions			$ 130.0	$ 145.0	$ 40.0
Estimated employer contributions in next 12 months	$ 87.0		$ 87.0
Percentage of total assets	90.00%		90.00%
Small annuity buy out [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Benefits paid			$ 86.0	$ 96.0
Small annuity buy out [Member] | Pension Benefits [Member] | United States
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Number of participants | employee			1,200	1,800
Percent of U.S. employees as participants			8.00%	10.00%