Derivative Instruments - Customer-Related Derivative Positions of Company (Detail) - Customer-Related Positions [Member] - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Derivative [Line Items]
Notional Value, Assets	$ 316,670	$ 294,310
Fair Value, Assets	3,867	5,552
Notional Value, Liabilities	303,453	282,040
Fair Value, Liabilities	2,461	3,054
Interest Rate Contracts [Member] | Receive Fixed/Pay Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	124,770	144,859
Fair Value, Assets	$ 2,398	$ 3,782
Derivative Asset Average Remaining Maturity Period	4 years 9 months 18 days	4 years 11 months 4 days
Notional Value, Liabilities	$ 46,250	$ 12,027
Fair Value, Liabilities	$ 296	$ 99
Derivative Liability Average Remaining Maturity Period	6 years 7 months 9 days	8 years 8 months 19 days
Interest Rate Contracts [Member] | Pay Fixed/Receive Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	$ 47,573	$ 15,048
Fair Value, Assets	$ 80	$ 2
Derivative Asset Average Remaining Maturity Period	6 years 7 months 24 days	8 years 5 months 4 days
Notional Value, Liabilities	$ 119,027	$ 134,963
Fair Value, Liabilities	$ 784	$ 1,239
Derivative Liability Average Remaining Maturity Period	4 years 6 months 3 days	4 years 8 months 15 days
Interest Rate Contracts [Member] | Other Derivatives [Member]
Derivative [Line Items]
Notional Value, Assets	$ 8,463	$ 9,921
Fair Value, Assets	$ 1	$ 6
Derivative Asset Average Remaining Maturity Period	3 years 11 months 23 days	3 years 9 months
Notional Value, Liabilities	$ 7,260	$ 6,387
Fair Value, Liabilities	$ 3	$ 3
Derivative Liability Average Remaining Maturity Period	4 years 7 months 28 days	4 years 2 months 19 days
Interest Rate Contracts [Member] | Options [Member] | Purchased [Member]
Derivative [Line Items]
Notional Value, Assets	$ 85,251	$ 72,655
Fair Value, Assets	$ 217	$ 111
Derivative Asset Average Remaining Maturity Period	1 year 3 months 14 days	1 year 4 months 24 days
Notional Value, Liabilities	$ 2,701	$ 1,454
Fair Value, Liabilities	$ 41	$ 46
Derivative Liability Average Remaining Maturity Period	1 year 10 months 9 days	2 years 11 months 15 days
Interest Rate Contracts [Member] | Options [Member] | Written [Member]
Derivative [Line Items]
Notional Value, Assets	$ 2,690	$ 1,736
Fair Value, Assets	$ 41	$ 46
Derivative Asset Average Remaining Maturity Period	1 year 10 months 6 days	2 years 9 months 3 days
Notional Value, Liabilities	$ 79,781	$ 68,205
Fair Value, Liabilities	$ 192	$ 81
Derivative Liability Average Remaining Maturity Period	1 year 2 months 23 days	1 year 3 months
Interest Rate Contracts [Member] | Futures [Member] | Purchased [Member]
Derivative [Line Items]
Notional Value, Assets	$ 3,456	$ 1,851
Derivative Asset Average Remaining Maturity Period	1 month 20 days	1 year 2 months 19 days
Notional Value, Liabilities	$ 318	$ 924
Derivative Liability Average Remaining Maturity Period	1 year 11 months 19 days	18 days
Interest Rate Contracts [Member] | Futures [Member] | Written [Member]
Derivative [Line Items]
Notional Value, Assets	$ 2,583
Derivative Asset Average Remaining Maturity Period	1 year 5 months 4 days
Notional Value, Liabilities	$ 565	$ 4,090
Derivative Liability Average Remaining Maturity Period	5 months 12 days	8 months 19 days
Foreign Exchange Rate Contracts [Member] | Forwards, Spots and Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	$ 38,518	$ 44,845
Fair Value, Assets	$ 1,112	$ 1,590
Derivative Asset Average Remaining Maturity Period	1 year 2 months 12 days	11 months 15 days
Notional Value, Liabilities	$ 39,988	$ 45,992
Fair Value, Liabilities	$ 1,121	$ 1,565
Derivative Liability Average Remaining Maturity Period	1 year 5 months 12 days	1 year 1 month 17 days
Foreign Exchange Option [Member] | Purchased [Member]
Derivative [Line Items]
Notional Value, Assets	$ 629	$ 519
Fair Value, Assets	$ 18	$ 14
Derivative Asset Average Remaining Maturity Period	11 months 15 days	10 months 24 days
Foreign Exchange Option [Member] | Written [Member]
Derivative [Line Items]
Notional Value, Liabilities	$ 629	$ 519
Fair Value, Liabilities	$ 18	$ 14
Derivative Liability Average Remaining Maturity Period	11 months 15 days	10 months 24 days
Credit Contracts [Member]
Derivative [Line Items]
Notional Value, Assets	$ 2,737	$ 2,876
Fair Value, Assets		$ 1
Derivative Asset Average Remaining Maturity Period	2 years 5 months 26 days	2 years 9 months
Notional Value, Liabilities	$ 6,934	$ 7,479
Fair Value, Liabilities	$ 6	$ 7
Derivative Liability Average Remaining Maturity Period	4 years 4 months 28 days	3 years 9 months 21 days