Expected Future Service to be Paid by Plans (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011
Pension benefits
Defined Benefit Plan Disclosure [Line Items]
2012	$ 31.8
2013	32.6
2014	33.5
2015	35.9
2016	38.7
2017-2021	221.4
Other Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
2012	3.3
2013	3.2
2014	3.1
2015	3.0
2016	2.9
2017-2021	$ 13.1

The amount of the aggregate benefits expected to be paid in the five fiscal years thereafter (the aggregate amount of benefits expected to be paid in years 6 through 10 after the date of the latest statement of financial position).

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 5

-Subparagraph f

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: 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=6962843&loc=d3e1928-114920

Name:	us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsInFiveFiscalYearsThereafter
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant