Derivative Positions (Additional Information) (Detail) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Derivative, Notional Amount	$ 232,120	$ 249,705
Credit Risk Contract [Member]
Derivative Asset, Notional Amount	7	4
Derivative Liability, Notional Amount	33	11
Other Contract [Member] | Visa Interest [Member]
Derivative Liability, Notional Amount	41	49
Interest rate futures [Member] | Mortgage Servicing Rights [Member]
Derivative, Notional Amount	5,600	16,600
Interest rate futures [Member] | Loans Held-For-Sale [Member]
Derivative, Notional Amount	302	190
Interest rate futures [Member] | Other Trading [Member]
Derivative, Notional Amount	4,900	9,800
Equity Futures [Member] | Equity Contract [Member]
Derivative, Notional Amount	$ 274	$ 1,222