Derivative Financial Instruments - Notional Value of Derivative Contracts (Detail) - USD ($) $ in Millions		Sep. 30, 2020	Dec. 31, 2019
Derivative [Line Items]
Total		$ 3,074,468	$ 4,807,851
Interest rate contracts [Member]
Derivative [Line Items]
Total		1,569,281	3,051,548
Interest Rate Futures and Forwards [Member]
Derivative [Line Items]
Total		298,841	597,980
Interest Rate Swap [Member]
Derivative [Line Items]
Total		1,166,115	2,130,442
Interest Rate Options Written [Member]
Derivative [Line Items]
Total		53,736	158,861
Interest Rate Options Purchased [Member]
Derivative [Line Items]
Total		50,589	164,265
Foreign exchange contracts [Member]
Derivative [Line Items]
Total		1,284,001	1,520,980
Foreign Exchange Swaps, Futures and Forwards [Member]
Derivative [Line Items]
Total		1,161,461	1,362,959
Foreign Exchange Options Written [Member]
Derivative [Line Items]
Total		37,854	44,876
Foreign Exchange Options Purchased [Member]
Derivative [Line Items]
Total		38,261	46,085
Foreign Exchange Spot [Member]
Derivative [Line Items]
Total		46,425	67,060
Commodities, equities and precious metals contracts [Member]
Derivative [Line Items]
Total		141,430	144,230
Commodities, Equities and Precious Metals, Swaps, Futures and Forwards [Member]
Derivative [Line Items]
Total		63,718	55,678
Commodities, Equities and Precious Metals Options Written [Member]
Derivative [Line Items]
Total		33,745	39,035
Commodities, Equities and Precious Metals Options Purchased [Member]
Derivative [Line Items]
Total		43,967	49,517
Credit contracts [Member]
Derivative [Line Items]
Total		78,645	90,049
Other Contracts [Member]
Derivative [Line Items]
Total	[1]	$ 1,111	$ 1,044

[1] Consists of swap agreements entered into in conjunction with the sales of Visa Class B Shares.