Derivative Financial Instruments - Notional Value of Derivative Contracts (Detail) - USD ($) $ in Millions		Sep. 30, 2018	Dec. 31, 2017
Derivative [Line Items]
Total		$ 5,434,475	$ 4,793,784
Interest rate contracts [Member]
Derivative [Line Items]
Total		4,092,831	3,593,216
Interest Rate Futures and Forwards [Member]
Derivative [Line Items]
Total		783,526	735,757
Interest Rate Swap [Member]
Derivative [Line Items]
Total		3,088,381	2,687,273
Interest Rate Options Written [Member]
Derivative [Line Items]
Total		102,741	77,144
Interest Rate Options Purchased [Member]
Derivative [Line Items]
Total		118,183	93,042
Foreign exchange contracts [Member]
Derivative [Line Items]
Total		1,114,608	996,092
Foreign Exchange Swaps, Futures and Forwards [Member]
Derivative [Line Items]
Total		1,006,804	924,163
Foreign Exchange Options Written [Member]
Derivative [Line Items]
Total		28,800	25,911
Foreign Exchange Options Purchased [Member]
Derivative [Line Items]
Total		29,183	26,617
Foreign Exchange Spot [Member]
Derivative [Line Items]
Total		49,821	19,401
Commodities, equities and precious metals contracts [Member]
Derivative [Line Items]
Total		125,100	113,542
Commodities, Equities and Precious Metals, Swaps, Futures and Forwards [Member]
Derivative [Line Items]
Total		49,408	38,709
Commodities, Equities and Precious Metals Options Written [Member]
Derivative [Line Items]
Total		31,982	31,631
Commodities, Equities and Precious Metals Options Purchased [Member]
Derivative [Line Items]
Total		43,710	43,202
Credit contracts [Member]
Derivative [Line Items]
Total		101,098	90,290
Other Contracts [Member]
Derivative [Line Items]
Total	[1]	$ 838	$ 644

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