Loans - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 67,338,000,000	$ 69,588,000,000	$ 72,563,000,000
Net deferred origination costs (fees)	88,000,000		81,000,000
Net unamortized premium (discount)	8,000,000		8,000,000
Commercial loans removed from TDR classification	0	$ 0
Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	47,739,000,000		53,035,000,000
Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 19,599,000,000		19,528,000,000
Weighted average rate of reduction	3.86%	1.63%
Affiliated Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 1,920,000,000	$ 939,000,000	$ 6,750,000,000