Derivative Financial Instruments - Notional Value of Derivative Contracts (Detail) - USD ($) $ in Millions		Jun. 30, 2018	Dec. 31, 2017
Derivative [Line Items]
Total		$ 5,550,836	$ 4,793,784
Interest rate contracts [Member]
Derivative [Line Items]
Total		4,165,174	3,593,216
Interest Rate Futures and Forwards [Member]
Derivative [Line Items]
Total		937,672	735,757
Interest Rate Swap [Member]
Derivative [Line Items]
Total		3,009,143	2,687,273
Interest Rate Options Written [Member]
Derivative [Line Items]
Total		100,512	77,144
Interest Rate Options Purchased [Member]
Derivative [Line Items]
Total		117,847	93,042
Foreign exchange contracts [Member]
Derivative [Line Items]
Total		1,160,829	996,092
Foreign Exchange Swaps, Futures and Forwards [Member]
Derivative [Line Items]
Total		1,061,194	924,163
Foreign Exchange Options Written [Member]
Derivative [Line Items]
Total		29,417	25,911
Foreign Exchange Options Purchased [Member]
Derivative [Line Items]
Total		29,916	26,617
Foreign Exchange Spot [Member]
Derivative [Line Items]
Total		40,302	19,401
Commodities, equities and precious metals contracts [Member]
Derivative [Line Items]
Total		133,004	113,542
Commodities, Equities and Precious Metals, Swaps, Futures and Forwards [Member]
Derivative [Line Items]
Total		53,437	38,709
Commodities, Equities and Precious Metals Options Written [Member]
Derivative [Line Items]
Total		33,847	31,631
Commodities, Equities and Precious Metals Options Purchased [Member]
Derivative [Line Items]
Total		45,720	43,202
Credit contracts [Member]
Derivative [Line Items]
Total		91,081	90,290
Other Contracts [Member]
Derivative [Line Items]
Total	[1]	$ 748	$ 644

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