Derivative Financial Instruments - Notional Value of Derivative Contracts (Detail) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Total		$ 4,793,784	$ 4,135,130
Interest rate contracts [Member]
Derivative [Line Items]
Total		3,593,216	2,805,579
Interest Rate Futures and Forwards [Member]
Derivative [Line Items]
Total		735,757	501,635
Interest Rate Swap [Member]
Derivative [Line Items]
Total		2,687,273	2,142,183
Interest Rate Options Written [Member]
Derivative [Line Items]
Total		77,144	74,741
Interest Rate Options Purchased [Member]
Derivative [Line Items]
Total		93,042	87,020
Foreign exchange contracts [Member]
Derivative [Line Items]
Total		996,092	1,105,971
Foreign Exchange Swaps, Futures and Forwards [Member]
Derivative [Line Items]
Total		924,163	965,301
Foreign Exchange Options Written [Member]
Derivative [Line Items]
Total		25,911	52,845
Foreign Exchange Options Purchased [Member]
Derivative [Line Items]
Total		26,617	53,260
Foreign Exchange Spot [Member]
Derivative [Line Items]
Total		19,401	34,565
Commodities, equities and precious metals contracts [Member]
Derivative [Line Items]
Total		113,542	99,682
Commodities, Equities and Precious Metals, Swaps, Futures and Forwards [Member]
Derivative [Line Items]
Total		38,709	49,555
Commodities, Equities and Precious Metals Options Written [Member]
Derivative [Line Items]
Total		31,631	19,495
Commodities, Equities and Precious Metals Options Purchased [Member]
Derivative [Line Items]
Total		43,202	30,632
Credit contracts [Member]
Derivative [Line Items]
Total		90,290	123,714
Other Contract [Member]
Derivative [Line Items]
Total	[1]	$ 644	$ 184

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