Derivative Instruments - Customer-Related Derivative Positions of Company (Detail) - Customer-Related Positions [Member] - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Derivative [Line Items]
Notional Value, Assets	$ 178,595	$ 156,822
Fair Value, Assets	1,716	2,319
Notional Value, Liabilities	166,374	140,485
Fair Value, Liabilities	1,924	2,195
Interest Rate Contracts [Member] | Receive Fixed/Pay Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	16,380	28,681
Fair Value, Assets	$ 394	$ 679
Derivative Asset Average Remaining Maturity Period	6 years 4 months 9 days	5 years 8 months 15 days
Notional Value, Liabilities	$ 84,602	$ 59,990
Fair Value, Liabilities	$ 861	$ 840
Derivative Liability Average Remaining Maturity Period	4 years 10 months 17 days	4 years 3 months 7 days
Interest Rate Contracts [Member] | Pay Fixed/Receive Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	$ 86,194	$ 63,038
Fair Value, Assets	$ 534	$ 860
Derivative Asset Average Remaining Maturity Period	4 years 8 months 19 days	4 years 2 months 12 days
Notional Value, Liabilities	$ 18,496	$ 25,093
Fair Value, Liabilities	$ 309	$ 602
Derivative Liability Average Remaining Maturity Period	5 years 21 days	5 years 9 months 3 days
Interest Rate Contracts [Member] | Options [Member] | Purchased [Member]
Derivative [Line Items]
Notional Value, Assets	$ 38,022	$ 29,091
Fair Value, Assets	$ 75	$ 22
Derivative Asset Average Remaining Maturity Period	1 year 6 months 29 days	1 year 7 months 9 days
Notional Value, Liabilities	$ 799	$ 880
Fair Value, Liabilities	$ 1	$ 14
Derivative Liability Average Remaining Maturity Period	4 years 4 months 20 days	4 years 2 months 26 days
Interest Rate Contracts [Member] | Options [Member] | Written [Member]
Derivative [Line Items]
Notional Value, Assets	$ 799	$ 880
Fair Value, Assets	$ 1	$ 15
Derivative Asset Average Remaining Maturity Period	4 years 4 months 20 days	4 years 2 months 26 days
Notional Value, Liabilities	$ 34,682	$ 27,056
Fair Value, Liabilities	$ 71	$ 20
Derivative Liability Average Remaining Maturity Period	1 year 5 months 4 days	1 year 6 months
Interest Rate Contracts [Member] | Futures [Member] | Written [Member]
Derivative [Line Items]
Notional Value, Assets	$ 8,626	$ 7,007
Fair Value, Assets	$ 11	$ 4
Derivative Asset Average Remaining Maturity Period	8 months 26 days	1 year 2 months 26 days
Foreign Exchange Rate Contracts [Member] | Forwards, Spots and Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	$ 25,311	$ 24,099
Fair Value, Assets	$ 637	$ 656
Derivative Asset Average Remaining Maturity Period	10 months 20 days	10 months 20 days
Notional Value, Liabilities	$ 24,532	$ 23,440
Fair Value, Liabilities	$ 618	$ 636
Derivative Liability Average Remaining Maturity Period	10 months 9 days	9 months 29 days
Foreign Exchange Option [Member] | Purchased [Member]
Derivative [Line Items]
Notional Value, Assets	$ 3,263	$ 4,026
Fair Value, Assets	$ 64	$ 83
Derivative Asset Average Remaining Maturity Period	10 months 9 days	1 year 2 months 12 days
Foreign Exchange Option [Member] | Written [Member]
Derivative [Line Items]
Notional Value, Liabilities	$ 3,263	$ 4,026
Fair Value, Liabilities	$ 64	$ 83
Derivative Liability Average Remaining Maturity Period	10 months 9 days	1 year 2 months 12 days