Derivative Instruments - Customer-Related Derivative Positions of Company (Detail) - Customer-Related Positions [Member] - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Derivative [Line Items]
Notional Value, Assets	$ 261,821	$ 242,263
Fair Value, Assets	6,567	2,755
Notional Value, Liabilities	255,754	248,893
Fair Value, Liabilities	3,510	1,682
Interest Rate Contracts [Member] | Receive Fixed/Pay Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	143,179	108,560
Fair Value, Assets	$ 4,551	$ 1,865
Derivative Asset Average Remaining Maturity Period	5 years 3 months 14 days	4 years 9 months 29 days
Notional Value, Liabilities	$ 1,947	$ 31,544
Fair Value, Liabilities	$ 5	$ 88
Derivative Liability Average Remaining Maturity Period	9 years 5 months 12 days	3 years 9 months 29 days
Interest Rate Contracts [Member] | Pay Fixed/Receive Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	$ 2,121	$ 28,150
Fair Value, Assets		$ 30
Derivative Asset Average Remaining Maturity Period	8 years 4 months 20 days	3 years 9 months 29 days
Notional Value, Liabilities	$ 137,866	$ 101,078
Fair Value, Liabilities	$ 1,515	$ 753
Derivative Liability Average Remaining Maturity Period	5 years 29 days	4 years 6 months 18 days
Interest Rate Contracts [Member] | Other Derivatives [Member]
Derivative [Line Items]
Notional Value, Assets	$ 6,641	$ 6,895
Fair Value, Assets	$ 2	$ 1
Derivative Asset Average Remaining Maturity Period	3 years 9 months 25 days	3 years 5 months 12 days
Notional Value, Liabilities	$ 8,423	$ 6,218
Fair Value, Liabilities	$ 3	$ 2
Derivative Liability Average Remaining Maturity Period	3 years 5 months 1 day	2 years 11 months 23 days
Interest Rate Contracts [Member] | Options [Member] | Purchased [Member]
Derivative [Line Items]
Notional Value, Assets	$ 59,554	$ 46,406
Fair Value, Assets	$ 94	$ 43
Derivative Asset Average Remaining Maturity Period	1 year 5 months 19 days	2 years 21 days
Notional Value, Liabilities	$ 3,624	$ 12,804
Fair Value, Liabilities	$ 347	$ 47
Derivative Liability Average Remaining Maturity Period	11 years 6 months 21 days	1 year 3 months
Interest Rate Contracts [Member] | Options [Member] | Written [Member]
Derivative [Line Items]
Notional Value, Assets	$ 3,722	$ 6,901
Fair Value, Assets	$ 348	$ 49
Derivative Asset Average Remaining Maturity Period	11 years 4 months 28 days	1 year 11 months 4 days
Notional Value, Liabilities	$ 53,430	$ 49,741
Fair Value, Liabilities	$ 67	$ 41
Derivative Liability Average Remaining Maturity Period	1 year 4 months 6 days	1 year 9 months 25 days
Interest Rate Contracts [Member] | Futures [Member] | Purchased [Member]
Derivative [Line Items]
Notional Value, Assets	$ 4,324	$ 894
Fair Value, Assets	$ 1
Derivative Asset Average Remaining Maturity Period	5 months 26 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	$ 5,518	$ 1,995
Fair Value, Liabilities	$ 15
Derivative Liability Average Remaining Maturity Period	1 year 18 days	1 year 14 days
Foreign Exchange Rate Contracts [Member] | Forwards, Spots and Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	$ 36,781	$ 36,350
Fair Value, Assets	$ 1,516	$ 748
Derivative Asset Average Remaining Maturity Period	10 months 24 days	11 months 19 days
Notional Value, Liabilities	$ 36,703	$ 36,671
Fair Value, Liabilities	$ 1,497	$ 729
Derivative Liability Average Remaining Maturity Period	1 year 25 days	1 year 25 days
Foreign Exchange Option [Member] | Purchased [Member]
Derivative [Line Items]
Notional Value, Assets	$ 1,345	$ 1,354
Fair Value, Assets	$ 43	$ 17
Derivative Asset Average Remaining Maturity Period	7 months 20 days	6 months 14 days
Foreign Exchange Option [Member] | Written [Member]
Derivative [Line Items]
Notional Value, Liabilities	$ 1,345	$ 1,354
Fair Value, Liabilities	$ 43	$ 17
Derivative Liability Average Remaining Maturity Period	7 months 20 days	6 months 14 days
Credit Contracts [Member]
Derivative [Line Items]
Notional Value, Assets	$ 4,154	$ 2,879
Fair Value, Assets	$ 12	$ 1
Derivative Asset Average Remaining Maturity Period	3 years 9 months 14 days	3 years 3 months 10 days
Notional Value, Liabilities	$ 6,898	$ 7,488
Fair Value, Liabilities	$ 18	$ 5
Derivative Liability Average Remaining Maturity Period	4 years 2 months 19 days	4 years 3 months 29 days