Derivative Instruments - Customer-Related Derivative Positions of Company (Detail) - Customer-Related Positions [Member] - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Derivative [Line Items]
Notional Value, Assets	$ 190,662	$ 182,021
Fair Value, Assets	2,018	1,855
Notional Value, Liabilities	191,363	183,744
Fair Value, Liabilities	1,435	1,670
Interest Rate Contracts [Member] | Receive Fixed/Pay Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	60,918	42,054
Fair Value, Assets	$ 1,140	$ 754
Derivative Asset Average Remaining Maturity Period	6 years 6 months 10 days	6 years 8 months 23 days
Notional Value, Liabilities	$ 50,227	$ 60,731
Fair Value, Liabilities	$ 220	$ 456
Derivative Liability Average Remaining Maturity Period	3 years 9 months 3 days	4 years 3 months 26 days
Interest Rate Contracts [Member] | Pay Fixed/Receive Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	$ 48,506	$ 60,970
Fair Value, Assets	$ 172	$ 288
Derivative Asset Average Remaining Maturity Period	3 years 7 months 24 days	3 years 10 months 24 days
Notional Value, Liabilities	$ 58,611	$ 40,499
Fair Value, Liabilities	$ 519	$ 420
Derivative Liability Average Remaining Maturity Period	6 years 4 months 28 days	6 years 6 months 26 days
Interest Rate Contracts [Member] | Other Derivatives [Member]
Derivative [Line Items]
Notional Value, Assets	$ 6,056	$ 5,777
Fair Value, Assets	$ 1	$ 2
Derivative Asset Average Remaining Maturity Period	3 years 7 months 2 days	3 years 9 months 7 days
Notional Value, Liabilities	$ 6,601	$ 6,496
Fair Value, Liabilities	$ 2	$ 2
Derivative Liability Average Remaining Maturity Period	3 years 21 days	2 years 8 months 19 days
Interest Rate Contracts [Member] | Options [Member] | Purchased [Member]
Derivative [Line Items]
Notional Value, Assets	$ 44,629	$ 41,711
Fair Value, Assets	$ 34	$ 51
Derivative Asset Average Remaining Maturity Period	1 year 4 months 9 days	1 year 6 months 14 days
Notional Value, Liabilities	$ 1,296	$ 1,940
Fair Value, Liabilities	$ 42	$ 30
Derivative Liability Average Remaining Maturity Period	9 years 3 months 29 days	1 year 11 months 23 days
Interest Rate Contracts [Member] | Options [Member] | Written [Member]
Derivative [Line Items]
Notional Value, Assets	$ 1,396	$ 2,060
Fair Value, Assets	$ 43	$ 32
Derivative Asset Average Remaining Maturity Period	8 years 11 months 1 day	2 years 25 days
Notional Value, Liabilities	$ 41,960	$ 39,538
Fair Value, Liabilities	$ 33	$ 51
Derivative Liability Average Remaining Maturity Period	1 year 3 months	1 year 5 months 8 days
Interest Rate Contracts [Member] | Futures [Member] | Purchased [Member]
Derivative [Line Items]
Notional Value, Assets	$ 1,085	$ 460
Fair Value, Assets	$ 1
Derivative Asset Average Remaining Maturity Period	1 year 3 months 10 days	1 year 6 months 29 days
Interest Rate Contracts [Member] | Futures [Member] | Written [Member]
Derivative [Line Items]
Notional Value, Liabilities	$ 3,634	$ 6,190
Fair Value, Liabilities	$ 3	$ 1
Derivative Liability Average Remaining Maturity Period	4 months 24 days	7 months 2 days
Foreign Exchange Rate Contracts [Member] | Forwards, Spots and Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	$ 26,279	$ 26,210
Fair Value, Assets	$ 597	$ 681
Derivative Asset Average Remaining Maturity Period	1 year 29 days	10 months 28 days
Notional Value, Liabilities	$ 26,515	$ 25,571
Fair Value, Liabilities	$ 585	$ 663
Derivative Liability Average Remaining Maturity Period	1 year 3 months	10 months 17 days
Foreign Exchange Option [Member] | Purchased [Member]
Derivative [Line Items]
Notional Value, Assets	$ 1,763	$ 2,779
Fair Value, Assets	$ 30	$ 47
Derivative Asset Average Remaining Maturity Period	10 months 9 days	9 months
Foreign Exchange Option [Member] | Written [Member]
Derivative [Line Items]
Notional Value, Liabilities	$ 1,763	$ 2,779
Fair Value, Liabilities	$ 30	$ 47
Derivative Liability Average Remaining Maturity Period	10 months 9 days	9 months
Credit Contracts [Member]
Derivative [Line Items]
Notional Value, Assets	$ 30
Derivative Asset Average Remaining Maturity Period	5 years 2 months 23 days
Notional Value, Liabilities	$ 756
Fair Value, Liabilities	$ 1
Derivative Liability Average Remaining Maturity Period	5 years 2 months 23 days