Composition of the Company's Loan Portfolio (Additional Information) (Detail) $ in Millions	Sep. 30, 2015 USD ($)	Dec. 31, 2014 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Weighted Average FICO Score on Mortgages With Potential Concentration of Credit Risk	744	738
Loans Receivable, Fair Value Disclosure	$ 262	$ 272
Loans Held-for-sale, Fair Value Disclosure	1,883	1,892
Residential Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Fair Value Disclosure	$ 262	$ 272