Loans - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 83,617,000,000	$ 72,198,000,000	$ 83,617,000,000	$ 72,198,000,000	$ 77,741,000,000
Net deferred origination fees	52,000,000		52,000,000		34,000,000
Net unamortized premium on loans	12,000,000		12,000,000		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	$ 20,021,000,000		$ 20,021,000,000		19,654,000,000
Weighted average rate of reduction	1.90%	1.52%	1.84%	1.51%
Affiliated Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 4,607,000,000		$ 4,607,000,000		$ 4,821,000,000