Variable Interest Entities - Principal Provisions of Debt (Parenthetical) (Detail) (USD $)	Jun. 30, 2013	Dec. 31, 2012
Subordinated Notes [Member]
Debt Instrument [Line Items]
Fair value of Senior Secured and Subordinated Notes	$ 10,835,000,000	$ 11,835,000,000
Variable Interest Entities [Member]
Debt Instrument [Line Items]
Fair value of the consolidated VIE assets	$ 14,150,000,000	$ 14,672,000,000

This item represents a financial instrument (as defined) for which it is not practicable to estimate fair value. Such disclosure may be for an individual financial instrument or a class of financial instruments.

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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