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Pension Plans - Defined Benefit Pension Plan (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Equity Securities [Member]
Plan asset allocation by category (%):
Total plan asset allocation by category	35.00%
Debt Securities [Member]
Plan asset allocation by category (%):
Total plan asset allocation by category	65.00%
United Kingdom Plan [Member]
Plan assumptions at December 31, (%):
Discount rate	2.48%	3.69%	3.55%
Inflation rate	2.25%	2.15%	2.15%
Rate of return on plan assets	3.20%	4.20%	4.05%
Plan asset allocation by category (%):
Total plan asset allocation by category	100.00%	100.00%	100.00%
United Kingdom Plan [Member] | Equity Securities [Member]
Plan assumptions at December 31, (%):
Rate of return on plan assets	5.80%	6.65%	6.50%
Plan asset allocation by category (%):
Total plan asset allocation by category	25.00%	34.00%	32.00%
United Kingdom Plan [Member] | Debt Securities [Member]
Plan assumptions at December 31, (%):
Rate of return on plan assets	2.05%	2.85%	2.75%
Plan asset allocation by category (%):
Total plan asset allocation by category	66.00%	62.00%	63.00%
United Kingdom Plan [Member] | Cash [Member]
Plan asset allocation by category (%):
Total plan asset allocation by category	9.00%	4.00%	5.00%
United Kingdom [Member] | Foreign Pension Plan [Member]
Plan net pension (credit)/charge:
Service cost	$ 1.0	$ 1.5	$ 1.7
Interest cost on PBO	20.7	27.7	34.7
Expected return on plan assets	(29.9)	(33.4)	(37.2)
Amortization of prior service credit	(1.1)	(1.2)	(1.3)
Amortization of actuarial net losses	2.6	5.2	5.4
Net pension charge	$ (6.7)	$ (0.2)	$ 3.3

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- Definition

Defined benefit plan assumptions used calculating net periodic benefit cost inflation rate.

+ References

No definition available.

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- Definition

The amount of gains or losses recognized in net periodic benefit cost.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (h)(4)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920

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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Prior Service Cost
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- Definition

The interest rate used to adjust for the time value of money.

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-Publisher FASB
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- Definition

An assumption as to the rate of return on plan assets reflecting the average rate of earnings expected on the funds invested or to be invested to provide for the benefits included in the benefit obligation.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Expected Long-Term Rate of Return on Plan Assets
-URI http://asc.fasb.org/extlink&oid=6512046

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- Definition

An amount calculated as a basis for determining the extent of delayed recognition of the effects of changes in the fair value of assets. The expected return on plan assets is determined based on the expected long-term rate of return on plan assets and the market-related value of plan assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Expected Return on Plan Assets
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- Definition

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.

+ References

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- Definition

The total amount of net periodic benefit cost for defined benefit plans for the period. Periodic benefit costs include the following components: service cost, interest cost, expected return on plan assets, gain (loss), prior service cost or credit, transition asset or obligation, and gain (loss) due to settlements or curtailments.

+ References

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

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Service Cost (Component of Net Periodic Pension Cost)
-URI http://asc.fasb.org/extlink&oid=6525008

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- Definition

Target allocation of investments of this type to total plan assets presented on a weighted average basis.

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