Derivative Positions (Additional Information) (Detail) - USD ($) shares in Millions, $ in Millions	1 Months Ended
	May 31, 2009	Dec. 31, 2017	Dec. 31, 2016
Derivative Asset, Notional Amount		$ 143,238	$ 127,456
Derivative Liability, Notional Amount		106,467	146,506
Credit Risk Contract [Member]
Derivative Asset, Notional Amount		4	5
Derivative Liability, Notional Amount		11	13
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		16,600	6,700
Interest rate futures [Member] | Loans Held For Sale [Member]
Derivative Asset, Notional Amount		190	720
Interest rate futures [Member] | Other Trading [Member]
Derivative Asset, Notional Amount		9,800	12,300
Equity Futures [Member] | Equity Contract [Member]
Derivative Asset, Notional Amount		$ 1,222	$ 629