Composition of the Company's Loan Portfolio (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013		Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Fair Value Disclosure	$ 316	[1]	$ 379	[1]
Residential Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Fair Value Disclosure	316		379
Residential Nonguaranteed [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Fair Value Disclosure	$ 316		$ 379

[1] 2 Includes loans of consolidated VIEs336 365