Loans - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 84,942,000,000	$ 73,439,000,000	$ 84,942,000,000	$ 73,439,000,000	$ 77,741,000,000
Net deferred origination fees	61,000,000		61,000,000		34,000,000
Net unamortized premium on loans	13,000,000		13,000,000		10,000,000
Commercial loans removed from TDR classification	0	$ 0	0	$ 0
Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 20,190,000,000		$ 20,190,000,000		19,654,000,000
Weighted average rate of reduction	1.62%	1.64%	1.76%	1.55%
Affiliated Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 5,447,000,000		$ 5,447,000,000		$ 4,821,000,000