Fair Value Measurements (Narrative) (Detail) (USD $)	Dec. 31, 2012	Dec. 31, 2011
Disclosure Fair Value Measurements Narrative [Abstract]
Net Assets Measured At Fair Value On A Recurring Basis	$ 1,800,000,000	$ 1,600,000,000
Net Assets Measured At Fair Value On A Recurring Basis Measured Using Unobservable Input And Classified As Level3	31,000,000	29,000,000
Fair value option of contractual principal outstanding		550,000,000
Nonrecurring fair values of leased assets		$ 50,000,000

This item represents the difference between the aggregate fair value and the aggregate unpaid principal balance of long-term debt instruments that have contractual principal amounts and for which the fair value option has been elected.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 28

-Subparagraph (d)(2)

-URI http://asc.fasb.org/extlink&oid=6957238&loc=d3e14064-108612

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 159

-Paragraph 18

-Subparagraph d(2)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant