Disclosures about Fair Value of Financial Instruments - Narrative (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for sale, average life from purchase to sale	16 days
Five-year Senior Unsecured Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Issuance of senior unsecured notes		$ 63

Represents the aggregate of total long-term debt, including current maturities and short-term debt.

No definition available.

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