Loans - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 68,063,000,000	$ 79,810,000,000	$ 68,063,000,000	$ 79,810,000,000	$ 73,875,000,000
Net deferred origination fees	25,000,000		25,000,000		48,000,000
Net unamortized premium (discount)	1,000,000		1,000,000		(5,000,000)
Commercial loans removed from TDR classification	0	0	0	0
Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	48,588,000,000		48,588,000,000		54,216,000,000
Loans which were classified as TDR loans during previous 12 months which became contractually delinquent	0	$ 0	0	$ 0
Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 19,475,000,000		$ 19,475,000,000		19,659,000,000
Weighted average rate of reduction	1.78%	1.54%	1.71%	1.68%
Loans which were classified as TDR loans during previous 12 months which became contractually delinquent	$ 2,000,000	$ 4,000,000	$ 5,000,000	$ 15,000,000
Affiliated Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 1,423,000,000	$ 5,072,000,000	$ 1,423,000,000	$ 5,072,000,000	$ 3,274,000,000