Derivative Instruments - Customer-Related Derivative Positions of Company (Detail) - Customer-Related Positions [Member] - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Derivative [Line Items]
Notional Value, Assets	$ 269,194	$ 242,263
Fair Value, Assets	6,131	2,755
Notional Value, Liabilities	268,762	248,893
Fair Value, Liabilities	2,801	1,682
Interest Rate Contracts [Member] | Receive Fixed/Pay Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	154,746	108,560
Fair Value, Assets	$ 4,788	$ 1,865
Derivative Asset Average Remaining Maturity Period	5 years 21 days	4 years 9 months 29 days
Notional Value, Liabilities	$ 949	$ 31,544
Fair Value, Liabilities	$ 11	$ 88
Derivative Liability Average Remaining Maturity Period	20 years 1 month 28 days	3 years 9 months 29 days
Interest Rate Contracts [Member] | Pay Fixed/Receive Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	$ 1,115	$ 28,150
Fair Value, Assets		$ 30
Derivative Asset Average Remaining Maturity Period	18 years 4 months 24 days	3 years 9 months 29 days
Notional Value, Liabilities	$ 148,543	$ 101,078
Fair Value, Liabilities	$ 1,501	$ 753
Derivative Liability Average Remaining Maturity Period	4 years 10 months 17 days	4 years 6 months 18 days
Interest Rate Contracts [Member] | Other Derivatives [Member]
Derivative [Line Items]
Notional Value, Assets	$ 8,264	$ 6,895
Fair Value, Assets	$ 2	$ 1
Derivative Asset Average Remaining Maturity Period	3 years 7 months 24 days	3 years 5 months 12 days
Notional Value, Liabilities	$ 8,538	$ 6,218
Fair Value, Liabilities	$ 5	$ 2
Derivative Liability Average Remaining Maturity Period	3 years 6 months 21 days	2 years 11 months 23 days
Interest Rate Contracts [Member] | Options [Member] | Purchased [Member]
Derivative [Line Items]
Notional Value, Assets	$ 61,304	$ 46,406
Fair Value, Assets	$ 113	$ 43
Derivative Asset Average Remaining Maturity Period	1 year 4 months 24 days	2 years 21 days
Notional Value, Liabilities	$ 3,878	$ 12,804
Fair Value, Liabilities	$ 210	$ 47
Derivative Liability Average Remaining Maturity Period	1 year 9 months 14 days	1 year 3 months
Interest Rate Contracts [Member] | Options [Member] | Written [Member]
Derivative [Line Items]
Notional Value, Assets	$ 2,806	$ 6,901
Fair Value, Assets	$ 213	$ 49
Derivative Asset Average Remaining Maturity Period	2 years 10 days	1 year 11 months 4 days
Notional Value, Liabilities	$ 57,736	$ 49,741
Fair Value, Liabilities	$ 82	$ 41
Derivative Liability Average Remaining Maturity Period	1 year 3 months	1 year 9 months 25 days
Interest Rate Contracts [Member] | Futures [Member] | Purchased [Member]
Derivative [Line Items]
Notional Value, Assets	$ 2,439	$ 894
Derivative Asset Average Remaining Maturity Period	4 months 6 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	$ 6,496	$ 1,995
Derivative Liability Average Remaining Maturity Period	1 year	1 year 14 days
Foreign Exchange Rate Contracts [Member] | Forwards, Spots and Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	$ 33,851	$ 36,350
Fair Value, Assets	$ 976	$ 748
Derivative Asset Average Remaining Maturity Period	1 year 2 months 8 days	11 months 19 days
Notional Value, Liabilities	$ 34,087	$ 36,671
Fair Value, Liabilities	$ 945	$ 729
Derivative Liability Average Remaining Maturity Period	1 year 3 months 14 days	1 year 25 days
Foreign Exchange Option [Member] | Purchased [Member]
Derivative [Line Items]
Notional Value, Assets	$ 1,021	$ 1,354
Fair Value, Assets	$ 32	$ 17
Derivative Asset Average Remaining Maturity Period	7 months 9 days	6 months 14 days
Foreign Exchange Option [Member] | Written [Member]
Derivative [Line Items]
Notional Value, Liabilities	$ 1,021	$ 1,354
Fair Value, Liabilities	$ 32	$ 17
Derivative Liability Average Remaining Maturity Period	7 months 9 days	6 months 14 days
Credit Contracts [Member]
Derivative [Line Items]
Notional Value, Assets	$ 3,648	$ 2,879
Fair Value, Assets	$ 7	$ 1
Derivative Asset Average Remaining Maturity Period	3 years 4 months 20 days	3 years 3 months 10 days
Notional Value, Liabilities	$ 7,514	$ 7,488
Fair Value, Liabilities	$ 15	$ 5
Derivative Liability Average Remaining Maturity Period	3 years 10 months 9 days	4 years 3 months 29 days