Loans - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 81,458,000,000	$ 68,897,000,000	$ 77,741,000,000
Net deferred origination fees	45,000,000		34,000,000
Net unamortized premium on loans	12,000,000		10,000,000
Commercial loans removed from TDR classification	0	0
Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	19,811,000,000		19,654,000,000
Weighted average rate of reduction	1.77%	1.50%
Affiliated Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 5,016,000,000		$ 4,821,000,000