Pension and Other Postretirement Benefits - Components of Net Periodic Benefit Cost (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	$ 288	$ 190	$ 155
Reduction in net periodic benefit cost for post retirement benefit due to drug benefit	$ 64	$ 43	$ 39

Amount of the reduction in the accumulated postretirement benefit obligation for the government subsidy related to prescription drug benefits attributed to past service. Disclosure relates to the first period in which an employer includes the effects of the subsidy in measuring the accumulated postretirement benefit obligation and net periodic postretirement benefit cost.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 60

-Section 50

-Paragraph 3

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6414203&loc=d3e39689-114964

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS106-2

-Paragraph 21

-Subparagraph a

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

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