Pension Plans - Movements in PBO and Fair Value of Plan Assets (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Change in PBO:
Actuarial losses/(gains)	$ 54.7	$ (6.7)	$ (58.5)
United Kingdom Plan [Member]
Change in PBO:
Service cost	1.7	1.6	1.6
Interest cost	34.7	31.3	32.2
Amortization of prior service cost/(credit)	(1.3)	(1.3)	(1.3)
Benefits paid	(47.6)	(39.4)
Fair value of plan assets:
Opening balance	790.3	768.6
Benefits paid	(47.6)	(39.4)
Actual contributions by employer	11.4	10.8
Actual return on assets	161.7	35.5
Exchange effect	(53.5)	14.8
Closing balance	862.3	790.3	768.6
German Plan [Member]
Change in PBO:
Opening balance	9.6	9.3
Service cost	0.2	0.2	0.1
Interest cost	0.3	0.3	0.3
Amortization of prior service cost/(credit)	0	(0.1)	0
Benefits paid	(0.2)	(0.2)
Actuarial losses/(gains)	1.8	(0.4)
Exchange effect	(1.3)	0.5
Closing balance	10.4	9.6	9.3
Fair value of plan assets:
Benefits paid	(0.2)	(0.2)
Pension Benefit Obligation [Member] \| United Kingdom Plan [Member]
Change in PBO:
Opening balance	819.8	805.3
Service cost	1.7	1.6
Interest cost	34.7	31.3
Benefits paid	(47.6)	(39.4)
Actuarial losses/(gains)	59.3	5.9
Exchange effect	(50.8)	15.1
Closing balance	817.1	819.8
Fair value of plan assets:
Benefits paid	$ (47.6)	$ (39.4)

The difference between fair value of plan assets at the end of the period and the fair value at the beginning of the period, adjusted for contributions and payments of benefits during the period, and after adjusting for taxes and other expenses, as applicable.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

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Amount of gain (loss) related to change in benefit obligation resulting from changes in actuarial assumptions, for example, but not limited to, interest, mortality, employee turnover, salary, and temporary deviation from the substantive plan.

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The amount of the prior service cost or credit recognized in net periodic benefit cost relating to benefit changes attributable to plan participants' prior service pursuant to a plan amendment or a plan initiation.

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This represents the entire assets recognized in the balance sheet that are associated with the defined benefit plans.

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1) For defined benefit pension plans, the benefit obligation is the projected benefit obligation, which is the actuarial present value as of a date of all benefits attributed by the pension benefit formula to employee service rendered prior to that date. 2) For other postretirement defined benefit plans, the benefit obligation is the accumulated postretirement benefit obligation, which is the actuarial present value of benefits attributed to employee service rendered to a particular date.

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The amount of payments made for which participants are entitled under a pension plan, including pension benefits, death benefits, and benefits due on termination of employment. Also includes payments made under a postretirement benefit plan, including prescription drug benefits, health care benefits, life insurance benefits, and legal, educational and advisory services. This item represents a periodic decrease to the plan obligations and a decrease to plan assets.

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The increase in the fair value of plan assets from contributions made by the employer.

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Amount of gain (loss) from foreign currency exchange rate changes for benefit obligation for plans of a foreign operation whose functional currency is not the reporting currency.

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The amount of increase or decrease in plan assets attributed to foreign currency changes. The effects of foreign currency exchange rate changes that are to be disclosed are those applicable to plans of a foreign operation whose functional currency is not the reporting currency.

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The increase in a defined benefit pension plan's projected benefit obligation or a defined benefit postretirement plan's accumulated postretirement benefit obligation due to the passage of time.

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The actuarial present value of benefits attributed by the pension benefit formula to services rendered by employees during the period. The portion of the expected postretirement benefit obligation attributed to employee service during the period. The service cost component is a portion of the benefit obligation and is unaffected by the funded status of the plan.

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