Loans - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 72,563,000,000	$ 73,875,000,000	$ 82,917,000,000
Loans outstanding to executive officers and directors as percent of total equity, maximum (percent)	5.00%	5.00%
Net deferred origination costs (fees)	$ 81,000,000	$ (48,000,000)
Net unamortized premium (discount)	8,000,000	(5,000,000)
Commercial loans removed from TDR classification	0	0	0
Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	53,035,000,000	54,216,000,000
Loans which were classified as TDR loans during previous 12 months which became contractually delinquent	0	0	$ 0
Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 19,528,000,000	$ 19,659,000,000
Weighted average rate of reduction	1.91%	1.48%	1.74%
Loans which were classified as TDR loans during previous 12 months which became contractually delinquent	$ 11,000,000	$ 24,000,000	$ 37,000,000
Affiliated Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 6,750,000,000	$ 3,274,000,000	$ 4,815,000,000