Derivative Financial Instruments - Notional Value of Derivative Contracts (Detail) - USD ($) $ in Millions		Dec. 31, 2018	Dec. 31, 2017
Derivative [Line Items]
Total		$ 5,556,668	$ 4,793,784
Interest rate contracts [Member]
Derivative [Line Items]
Total		4,203,667	3,593,216
Interest Rate Futures and Forwards [Member]
Derivative [Line Items]
Total		787,049	735,757
Interest Rate Swap [Member]
Derivative [Line Items]
Total		3,203,048	2,687,273
Interest Rate Options Written [Member]
Derivative [Line Items]
Total		106,009	77,144
Interest Rate Options Purchased [Member]
Derivative [Line Items]
Total		107,561	93,042
Foreign exchange contracts [Member]
Derivative [Line Items]
Total		1,144,808	996,092
Foreign Exchange Swaps, Futures and Forwards [Member]
Derivative [Line Items]
Total		1,052,088	924,163
Foreign Exchange Options Written [Member]
Derivative [Line Items]
Total		30,567	25,911
Foreign Exchange Options Purchased [Member]
Derivative [Line Items]
Total		31,069	26,617
Foreign Exchange Spot [Member]
Derivative [Line Items]
Total		31,084	19,401
Commodities, equities and precious metals contracts [Member]
Derivative [Line Items]
Total		110,159	113,542
Commodities, Equities and Precious Metals, Swaps, Futures and Forwards [Member]
Derivative [Line Items]
Total		41,328	38,709
Commodities, Equities and Precious Metals Options Written [Member]
Derivative [Line Items]
Total		28,595	31,631
Commodities, Equities and Precious Metals Options Purchased [Member]
Derivative [Line Items]
Total		40,236	43,202
Credit contracts [Member]
Derivative [Line Items]
Total		97,298	90,290
Other Contracts [Member]
Derivative [Line Items]
Total	[1]	$ 736	$ 644

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