Retirement Benefits - Information Comparing Plan Assets to Plan Obligations (Details) $ in Millions		3 Months Ended		12 Months Ended
	Oct. 08, 2019 USD ($) participant	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Total
Information for pension plans with an ABO in excess of plan assets:
Fair value of plan assets		$ 809.4	$ 750.1	$ 809.4	$ 750.1
Accumulated benefit obligation		1,057.6	951.0	1,057.6	951.0
Projected benefit obligation		1,083.3	968.9	1,083.3	968.9
Primary U.S. pension plan obligation settled				0.7	54.5
Settlement charge				(2.4)	(21.4)	$ (1.7)
U.S. Plans
Information for pension plans with an ABO in excess of plan assets:
Fair value of plan assets		747.1	699.3	747.1	699.3
Accumulated benefit obligation		908.0	826.8	908.0	826.8
Projected benefit obligation		908.0	826.8	908.0	826.8
Primary U.S. pension plan obligation settled				0.0	53.6
Settlement charge				0.0	(19.3)	0.0
U.S. Plans | Total
Information for pension plans with an ABO in excess of plan assets:
Annuity buy out number of participants | participant	2,600
Plan asset payment for settlement	$ 53.0
Primary U.S. pension plan obligation settled	$ 54.0
Settlement charge		19.3	19.3
Non-U.S. Plans
Information for pension plans with an ABO in excess of plan assets:
Fair value of plan assets		62.3	50.8	62.3	50.8
Accumulated benefit obligation		149.6	124.2	149.6	124.2
Projected benefit obligation		$ 175.3	$ 142.1	175.3	142.1
Primary U.S. pension plan obligation settled				0.7	0.9
Settlement charge				$ (2.4)	$ (2.1)	$ (1.7)