Loans - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 68,978,000,000	$ 72,563,000,000	$ 73,875,000,000
Net deferred origination costs (fees)	77,000,000	81,000,000
Net unamortized premium (discount)	11,000,000	8,000,000
Commercial loans removed from TDR classification	0	0	0
Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	49,342,000,000	53,035,000,000
Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	19,636,000,000	19,528,000,000
Affiliated Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 2,274,000,000	$ 6,750,000,000	$ 3,274,000,000
Loans outstanding to executive officers and director as percent of shareholders' equity, maximum (percent)	5.00%	5.00%