Loans - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 67,593,000,000	$ 77,625,000,000	$ 67,593,000,000	$ 77,625,000,000	$ 73,875,000,000
Net deferred origination fees	23,000,000		23,000,000		48,000,000
Net unamortized premium (discount)	6,000,000		6,000,000		(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	48,128,000,000		48,128,000,000		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	$ 19,465,000,000		$ 19,465,000,000		19,659,000,000
Weighted average rate of reduction	2.41%	1.41%	1.98%	1.61%
Loans which were classified as TDR loans during previous 12 months which became contractually delinquent	$ 3,000,000	$ 6,000,000	$ 8,000,000	$ 21,000,000
Affiliated Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 1,820,000,000	$ 4,463,000,000	$ 1,820,000,000	$ 4,463,000,000	$ 3,274,000,000