Pension and Post-Employment Benefits - Movements in PBO and Fair Value of Plan Assets (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Change in PBO:
Actuarial losses/(gains)	$ 69.9	$ (28.2)	$ 7.7
Fair value of plan assets:
Opening balance	159.8
Settlements	0.0	(10.6)
Closing balance	48.1	159.8
United Kingdom Plan [Member]
Change in PBO:
Benefits paid	(45.6)	(37.3)
Fair value of plan assets:
Opening balance	838.9	876.7
Benefits paid	(45.6)	(37.3)
Actual return on assets	(258.7)	17.5
Exchange effect	(82.5)	(7.4)
Closing balance	452.1	838.9	876.7
German Plan [Member]
Change in PBO:
Opening balance	13.2	15.2
Interest cost	0.1	0.1	0.1
Service cost	0.1	0.1	0.1
Benefits paid	(0.3)	(0.4)
Actuarial losses/(gains)	(4.0)	(0.7)
Exchange effect	(0.9)	(1.1)
Closing balance	8.2	13.2	15.2
Fair value of plan assets:
Benefits paid	(0.3)	(0.4)
Pension Benefit Obligation [Member]
Change in PBO:
Settlements	(10.6)
Pension Benefit Obligation [Member] \| United Kingdom Plan [Member]
Change in PBO:
Opening balance	679.1	758.7
Interest cost	10.1	7.6
Service cost	2.2	1.6
Benefits paid	(45.6)	(37.3)
Settlements	0.0	(10.6)
Plan amendments	0.4	5.4
Actuarial losses/(gains)	(174.2)	(40.5)
Exchange effect	(68.0)	(5.8)
Closing balance	404.0	679.1	$ 758.7
Fair value of plan assets:
Benefits paid	$ (45.6)	$ (37.3)

Amount of increase (decrease) in plan assets of defined benefit plan from actual return (loss) determined by change in fair value of plan assets adjusted for contributions, benefit payments, and other expenses.

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Amount of gain (loss) from change in actuarial assumptions which (increases) decreases benefit obligation of defined benefit plan. Assumptions include, but are not limited to, interest, mortality, employee turnover, salary, and temporary deviation from substantive plan.

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Amount of asset, recognized in statement of financial position, for overfunded defined benefit pension and other postretirement plans.

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Amount of actuarial present value of benefits attributed to service rendered by employee for defined benefit plan.

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Amount of payment to participant of defined benefit plan which decreases benefit obligation. For pension plan, payment includes, but is not limited to, pension benefits and death benefits. For other postretirement plan, payment includes, but is not limited to, prescription drug benefits, health care benefits, life insurance benefits, and legal, educational and advisory services.

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

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

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Amount of foreign currency translation gain (loss) which (increases) decreases benefit obligation of defined benefit plan.

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Amount of cost recognized for passage of time related to defined benefit plan.

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Amount of increase (decrease) in benefit obligation of defined benefit plan from change in terms of existing plan or initiation of new plan.

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Amount of foreign currency translation gain (loss) which increases (decreases) plan assets of defined benefit plan.

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Amount of cost for actuarial present value of benefits attributed to service rendered by employee for defined benefit plan.

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Amount of (increase) decrease to benefit obligation of defined benefit plan from irrevocable action relieving primary responsibility for benefit obligation and eliminating risk for obligation and assets used to effect settlement. Includes, but is not limited to, lump-sum cash payment to participant in exchange for right to receive specified benefits, purchase of nonparticipating annuity contract and change from remeasurement.

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Amount of payment, which decreases plan assets of defined benefit plan, for irrevocable action relieving primary responsibility for benefit obligation and eliminating risk for obligation and assets used to effect settlement. Transaction constituting settlement includes, but is not limited to, making lump-sum cash payment to participant in exchange for their rights to receive specified benefits and purchasing nonparticipating annuity contract.

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