Payment Status for the LHFI Portfolio (Parenthetical) (Detail) (USD $)	Sep. 30, 2012		Dec. 31, 2011
Financing Receivable, Impaired [Line Items]
Loans carried at fair value	$ 390,000,000	[1]	$ 433,000,000	[1]
Nonaccruing 90 Plus Days Past Due	1,300,000,000		2,300,000,000
Residential Portfolio Segment [Member]
Financing Receivable, Impaired [Line Items]
Loans carried at fair value	390,000,000		431,000,000
Residential Portfolio Segment [Member] | Residential Nonguaranteed [Member]
Financing Receivable, Impaired [Line Items]
Loans carried at fair value	$ 390,000,000		$ 431,000,000

[1] 2 Includes loans of consolidated VIEs374 3,322