Loans - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 79,810,000,000	$ 83,617,000,000	$ 79,810,000,000	$ 83,617,000,000	$ 82,917,000,000
Net deferred origination fees	57,000,000		57,000,000		62,000,000
Net unamortized premium on loans	15,000,000		15,000,000		16,000,000
Commercial loans removed from TDR classification	0	$ 0	0	$ 0
Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 20,267,000,000		$ 20,267,000,000		20,464,000,000
Weighted average rate of reduction	1.54%	1.90%	1.68%	1.84%
Affiliated Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 5,072,000,000	$ 4,607,000,000	$ 5,072,000,000	$ 4,607,000,000	$ 4,815,000,000