Derivative Positions (Additional Information) (Detail) - USD ($) shares in Millions, $ in Millions	1 Months Ended
	May 31, 2009	Mar. 31, 2018		Dec. 31, 2017
Derivative Asset, Notional Amount		$ 129,913	[1]	$ 143,238
Derivative Liability, Notional Amount		109,764	[1]	106,467
Credit Risk Contract [Member]
Derivative Asset, Notional Amount		5		4
Derivative Liability, Notional Amount		17		11
Other Contract [Member] | Visa Interest [Member]
Derivative Liability, Notional Amount		49		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 Liability, Notional Amount		2,000		16,600
Interest rate futures [Member] | Loans Held-For-Sale [Member]
Derivative Asset, Notional Amount		330		190
Interest rate futures [Member] | Other Trading [Member]
Derivative Asset, Notional Amount		9,700		9,800
Equity Futures [Member] | Equity Contract [Member]
Derivative Asset, Notional Amount		$ 1,337		$ 1,222

[1] For centrally-cleared derivatives, notional amounts are presented based on the fair value of the related derivative asset or derivative liability after applying variation margin.