Earnings per Share - Additional Information (Detail) (USD $) Share data in Millions, unless otherwise specified	12 Months Ended	0 Months Ended	1 Months Ended	12 Months Ended	20 Months Ended
Dec. 31, 2012	Dec. 31, 2010	May 10, 2011 Accelerated Share Repurchase Program	Nov. 17, 2011 Accelerated Share Repurchase Program	Dec. 31, 2011 Accelerated Share Repurchase Program	Dec. 31, 2012 Share Repurchase Program
Earnings Per Share [Line Items]
Stock repurchase program, authorized amount						$ 1,000,000,000
Stock repurchase program, authorized amount					$ 500,000,000
Treasury stock, shares acquired	0	0	19.9	9.3	29.2

Number of shares that have been repurchased during the period and are being held in treasury.

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 29, 30

-Article 5

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

-Publisher AICPA

-Name Accounting Principles Board Opinion (APB)

-Number 12

-Paragraph 10

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644

Name:	us-gaap_TreasuryStockSharesAcquired
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration