Loans - Additional Information (Detail) (USD $)	36 Months Ended	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 77,741,000,000	$ 77,741,000,000	$ 67,695,000,000	63,258,000,000
Net deferred origination fees	34,000,000	34,000,000	23,000,000
Net unamortized premium on loans	10,000,000	10,000,000	16,000,000
Commercial loans removed from TDR classification	0
Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	19,654,000,000	19,654,000,000	19,201,000,000
Weighted average rate of reduction		1.64%	1.94%	1.85%
Affiliated Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 4,821,000,000	$ 4,821,000,000	$ 5,328,000,000