Disclosures About Fair Value of Financial Instruments - Narrative (Detail) $ in Millions	9 Months Ended
	Sep. 30, 2015 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for sale, average life from purchase to sale	19 days
Five-year Senior Unsecured Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Issuance of senior unsecured notes	$ 63
Unsecured Debt | Five-year Senior Unsecured Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Senior unsecured notes term (years)	5 years