Employee Benefit Plans Net Periodic Benefit Cost (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Pension Plan | UNITED KINGDOM
Defined Benefit Plans and Other Postretirement Benefit Plans
Service Cost	$ 0.0	$ 0.0
Interest Cost	1.1	1.2
Expected Return on Plan Assets	(2.5)	(2.4)
Amortization of Net Actuarial Loss	0.3	0.3
Amortization of Prior Service Cost (Credit)	0.0	0.0
Net Periodic Benefit Cost	(1.1)	(0.9)
Pension Plan | UNITED STATES
Defined Benefit Plans and Other Postretirement Benefit Plans
Service Cost	2.4	2.8
Interest Cost	16.3	18.2
Expected Return on Plan Assets	(25.2)	(26.7)
Amortization of Net Actuarial Loss	5.3	4.7
Amortization of Prior Service Cost (Credit)	0.0	0.0
Net Periodic Benefit Cost	(1.2)	(1.0)
Other Postretirement Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans
Service Cost	0.0	0.0
Interest Cost	0.8	1.0
Expected Return on Plan Assets	(0.1)	(0.1)
Amortization of Net Actuarial Loss	0.0	0.0
Amortization of Prior Service Cost (Credit)	(0.1)	(0.1)
Net Periodic Benefit Cost	$ 0.6	$ 0.8