Summary of Estimated Benefit Payments (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012
Qualified Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
2013	$ 39.1
2014	39.8
2015	40.5
2016	40.3
2017	41.8
2018 - 2022	208.0
Non Qualified Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
2013	3.1
2014	3.2
2015	3.4
2016	3.1
2017	3.0
2018 - 2022	14.3
Chaucer Pension Scheme
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
2013	2.5
2014	2.6
2015	2.7
2016	2.8
2017	2.9
2018 - 2022	$ 15.9

Amount of benefits expected to be paid in the five fiscal years after the fifth fiscal year following the latest fiscal year from a defined benefit plan.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (f)

-URI http://asc.fasb.org/extlink&oid=21915506&loc=d3e1928-114920

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Amount of benefits expected to be paid in the next fiscal year following the latest fiscal year from a defined benefit plan.

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Amount of benefits expected to be paid in the fifth fiscal year following the latest fiscal year from a defined benefit plan.

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Amount of benefits expected to be paid in the fourth fiscal year following the latest fiscal year from a defined benefit plan.

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Amount of benefits expected to be paid in the third fiscal year following the latest fiscal year from a defined benefit plan.

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Amount of benefits expected to be paid in the second fiscal year following the latest fiscal year from a defined benefit plan.

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