Benefit Obligations - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended
Jun. 30, 2013
Defined Benefit Pension Plans and Defined Benefit Postretirement Plans Disclosure [Abstract]
Interest per year on cash-balance accounts	4.00%
Company contribution to pension plans	$ 26.3
Expected contribution to pension plan for the remainder of 2013	$ 25.5

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

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (b)(3)

-URI http://asc.fasb.org/extlink&oid=28361610&loc=d3e1928-114920

Name:	us-gaap_DefinedBenefitPlanContributionsByEmployer
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration