Derivative Positions (Additional Information) (Detail) - USD ($) shares in Millions, $ in Millions	1 Months Ended
	May 31, 2009	Jun. 30, 2018	Dec. 31, 2017
Derivative, Notional Amount		$ 230,681	$ 249,705
Credit Risk Contract [Member]
Derivative Asset, Notional Amount		6	4
Derivative Liability, Notional Amount		28	11
Other Contract [Member] | Visa Interest [Member]
Derivative Liability, Notional Amount		49
Derivative Financial Instruments, Liabilities [Member] | Visa Interest [Member]
Number Of Shares Sold To Selected Financial Institutions	3.2
Interest rate futures [Member] | Mortgage Servicing Rights [Member]
Derivative, Notional Amount		4,500	16,600
Interest rate futures [Member] | Loans Held-For-Sale [Member]
Derivative, Notional Amount		305	190
Interest rate futures [Member] | Other Trading [Member]
Derivative, Notional Amount		6,400	9,800
Equity Futures [Member] | Equity Contract [Member]
Derivative, Notional Amount		$ 406	$ 1,222