Derivative Instruments - Customer-Related Derivative Positions of Company (Detail) - Customer-Related Positions [Member] - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Derivative [Line Items]
Notional Value, Assets	$ 173,649	$ 156,822
Fair Value, Assets	1,726	2,319
Notional Value, Liabilities	166,972	140,485
Fair Value, Liabilities	1,842	2,195
Interest Rate Contracts [Member] | Receive Fixed/Pay Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	24,816	28,681
Fair Value, Assets	$ 470	$ 679
Derivative Asset Average Remaining Maturity Period	5 years 11 months 4 days	5 years 8 months 16 days
Notional Value, Liabilities	$ 76,059	$ 59,990
Fair Value, Liabilities	$ 733	$ 840
Derivative Liability Average Remaining Maturity Period	4 years 6 months 18 days	4 years 3 months 8 days
Interest Rate Contracts [Member] | Pay Fixed/Receive Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	$ 72,131	$ 63,038
Fair Value, Assets	$ 464	$ 860
Derivative Asset Average Remaining Maturity Period	4 years 6 months	4 years 2 months 12 days
Notional Value, Liabilities	$ 24,623	$ 25,093
Fair Value, Liabilities	$ 353	$ 602
Derivative Liability Average Remaining Maturity Period	6 years 1 month 9 days	5 years 9 months 3 days
Interest Rate Contracts [Member] | Options [Member] | Purchased [Member]
Derivative [Line Items]
Notional Value, Assets	$ 37,827	$ 29,091
Fair Value, Assets	$ 65	$ 22
Derivative Asset Average Remaining Maturity Period	1 year 7 months 17 days	1 year 7 months 10 days
Notional Value, Liabilities	$ 1,360	$ 880
Fair Value, Liabilities	$ 9	$ 14
Derivative Liability Average Remaining Maturity Period	3 years 11 days	4 years 2 months 27 days
Interest Rate Contracts [Member] | Options [Member] | Written [Member]
Derivative [Line Items]
Notional Value, Assets	$ 1,360	$ 880
Fair Value, Assets	$ 11	$ 15
Derivative Asset Average Remaining Maturity Period	3 years 11 days	4 years 2 months 27 days
Notional Value, Liabilities	$ 34,942	$ 27,056
Fair Value, Liabilities	$ 61	$ 20
Derivative Liability Average Remaining Maturity Period	1 year 5 months 20 days	1 year 6 months
Interest Rate Contracts [Member] | Futures [Member] | Purchased [Member]
Derivative [Line Items]
Notional Value, Assets	$ 40
Derivative Asset Average Remaining Maturity Period	1 year 8 months 19 days
Interest Rate Contracts [Member] | Futures [Member] | Written [Member]
Derivative [Line Items]
Notional Value, Assets	$ 7,588	$ 7,007
Fair Value, Assets	$ 10	$ 4
Derivative Asset Average Remaining Maturity Period	11 months 23 days	1 year 2 months 16 days
Notional Value, Liabilities	$ 800
Derivative Liability Average Remaining Maturity Period	2 months 19 days
Foreign Exchange Rate Contracts [Member] | Forwards, Spots and Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	$ 24,755	$ 24,099
Fair Value, Assets	$ 621	$ 656
Derivative Asset Average Remaining Maturity Period	10 months 17 days	9 months 22 days
Notional Value, Liabilities	$ 24,056	$ 23,440
Fair Value, Liabilities	$ 601	$ 636
Derivative Liability Average Remaining Maturity Period	10 months 28 days	9 months 29 days
Foreign Exchange Option [Member] | Purchased [Member]
Derivative [Line Items]
Notional Value, Assets	$ 5,132	$ 4,026
Fair Value, Assets	$ 85	$ 83
Derivative Asset Average Remaining Maturity Period	9 months 3 days	1 year 2 months 12 days
Foreign Exchange Option [Member] | Written [Member]
Derivative [Line Items]
Notional Value, Liabilities	$ 5,132	$ 4,026
Fair Value, Liabilities	$ 85	$ 83
Derivative Liability Average Remaining Maturity Period	9 months 3 days	1 year 2 months 12 days