Derivative Instruments - Customer-Related Derivative Positions of Company (Detail) - Customer-Related Positions [Member] - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Derivative [Line Items]
Notional Value, Assets	$ 273,525	$ 242,263
Fair Value, Assets	5,665	2,755
Notional Value, Liabilities	269,566	248,893
Fair Value, Liabilities	2,619	1,682
Interest Rate Contracts [Member] | Receive Fixed/Pay Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	149,619	108,560
Fair Value, Assets	$ 4,432	$ 1,865
Derivative Asset Average Remaining Maturity Period	5 years 7 days	4 years 9 months 29 days
Notional Value, Liabilities	$ 4,983	$ 31,544
Fair Value, Liabilities	$ 38	$ 88
Derivative Liability Average Remaining Maturity Period	10 years 7 months 17 days	3 years 9 months 29 days
Interest Rate Contracts [Member] | Pay Fixed/Receive Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	$ 5,479	$ 28,150
Fair Value, Assets	$ 3	$ 30
Derivative Asset Average Remaining Maturity Period	10 years 3 months 21 days	3 years 9 months 29 days
Notional Value, Liabilities	$ 142,997	$ 101,078
Fair Value, Liabilities	$ 1,409	$ 753
Derivative Liability Average Remaining Maturity Period	4 years 9 months 29 days	4 years 6 months 18 days
Interest Rate Contracts [Member] | Other Derivatives [Member]
Derivative [Line Items]
Notional Value, Assets	$ 9,049	$ 6,895
Fair Value, Assets	$ 2	$ 1
Derivative Asset Average Remaining Maturity Period	3 years 6 months 10 days	3 years 5 months 12 days
Notional Value, Liabilities	$ 7,490	$ 6,218
Fair Value, Liabilities	$ 3	$ 2
Derivative Liability Average Remaining Maturity Period	3 years 7 months 2 days	2 years 11 months 23 days
Interest Rate Contracts [Member] | Options [Member] | Purchased [Member]
Derivative [Line Items]
Notional Value, Assets	$ 65,401	$ 46,406
Fair Value, Assets	$ 110	$ 43
Derivative Asset Average Remaining Maturity Period	1 year 4 months 9 days	2 years 21 days
Notional Value, Liabilities	$ 3,119	$ 12,804
Fair Value, Liabilities	$ 64	$ 47
Derivative Liability Average Remaining Maturity Period	2 years 1 month 6 days	1 year 3 months
Interest Rate Contracts [Member] | Options [Member] | Written [Member]
Derivative [Line Items]
Notional Value, Assets	$ 3,310	$ 6,901
Fair Value, Assets	$ 65	$ 49
Derivative Asset Average Remaining Maturity Period	2 years 2 months 8 days	1 year 11 months 4 days
Notional Value, Liabilities	$ 60,533	$ 49,741
Fair Value, Liabilities	$ 76	$ 41
Derivative Liability Average Remaining Maturity Period	1 year 2 months 23 days	1 year 9 months 25 days
Interest Rate Contracts [Member] | Futures [Member] | Purchased [Member]
Derivative [Line Items]
Notional Value, Assets	$ 1,463	$ 894
Derivative Asset Average Remaining Maturity Period	8 months 15 days	2 months 15 days
Interest Rate Contracts [Member] | Futures [Member] | Written [Member]
Derivative [Line Items]
Notional Value, Assets		$ 3,874
Fair Value, Assets		$ 1
Derivative Asset Average Remaining Maturity Period		1 year 2 months 4 days
Notional Value, Liabilities	$ 5,682	$ 1,995
Derivative Liability Average Remaining Maturity Period	9 months 7 days	1 year 14 days
Foreign Exchange Rate Contracts [Member] | Forwards, Spots and Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	$ 35,624	$ 36,350
Fair Value, Assets	$ 1,029	$ 748
Derivative Asset Average Remaining Maturity Period	1 year 1 month 24 days	11 months 19 days
Notional Value, Liabilities	$ 36,540	$ 36,671
Fair Value, Liabilities	$ 998	$ 729
Derivative Liability Average Remaining Maturity Period	1 year 4 months 9 days	1 year 25 days
Foreign Exchange Option [Member] | Purchased [Member]
Derivative [Line Items]
Notional Value, Assets	$ 744	$ 1,354
Fair Value, Assets	$ 22	$ 17
Derivative Asset Average Remaining Maturity Period	8 months 26 days	6 months 14 days
Foreign Exchange Option [Member] | Written [Member]
Derivative [Line Items]
Notional Value, Liabilities	$ 744	$ 1,354
Fair Value, Liabilities	$ 22	$ 17
Derivative Liability Average Remaining Maturity Period	8 months 26 days	6 months 14 days
Credit Contracts [Member]
Derivative [Line Items]
Notional Value, Assets	$ 2,836	$ 2,879
Fair Value, Assets	$ 2	$ 1
Derivative Asset Average Remaining Maturity Period	2 years 10 months 17 days	3 years 3 months 10 days
Notional Value, Liabilities	$ 7,478	$ 7,488
Fair Value, Liabilities	$ 9	$ 5
Derivative Liability Average Remaining Maturity Period	3 years 10 months 2 days	4 years 3 months 29 days