Loans - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 73,875,000,000	$ 82,917,000,000	$ 77,741,000,000
Loans outstanding to executive officers and directors as percent of shareholders' equity, maximum (percent)	5.00%	5.00%
Net deferred origination fees	$ 48,000,000	$ 62,000,000
Net unamortized premium (discount)	(5,000,000)	16,000,000
Commercial loans removed from TDR classification	0	0	0
Loans which were classified as TDR loans during previous 12 months which became contractually delinquent	24,000,000	37,000,000	$ 34,000,000
Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 19,659,000,000	$ 20,464,000,000
Weighted average rate of reduction	1.48%	1.74%	1.64%
Loans which were classified as TDR loans during previous 12 months which became contractually delinquent	$ 24,000,000	$ 37,000,000	$ 34,000,000
Affiliated Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 3,274,000,000	$ 4,815,000,000	$ 4,821,000,000