Derivative Instruments - Customer-Related Derivative Positions of Company (Detail) - Customer-Related Positions [Member] - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2015
Derivative [Line Items]
Notional Value, Assets	$ 108,933	$ 72,112
Fair Value, Assets	3,050	2,046
Notional Value, Liabilities	108,397	80,044
Fair Value, Liabilities	3,153	2,099
Interest Rate Contracts [Member] | Receive Fixed/Pay Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	56,962	32,647
Fair Value, Assets	$ 2,249	$ 1,097
Derivative Asset Average Remaining Maturity Period	5 years 15 days	5 years 8 months 9 days
Notional Value, Liabilities	$ 14,464	$ 14,068
Fair Value, Liabilities	$ 29	$ 54
Derivative Liability Average Remaining Maturity Period	3 years 2 months 1 day	4 years 8 months 16 days
Interest Rate Contracts [Member] | Pay Fixed/Receive Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	$ 11,835	$ 10,685
Fair Value, Assets	$ 29	$ 43
Derivative Asset Average Remaining Maturity Period	2 years 9 months 22 days	4 years 6 months 18 days
Notional Value, Liabilities	$ 59,866	$ 35,045
Fair Value, Liabilities	$ 2,385	$ 1,160
Derivative Liability Average Remaining Maturity Period	5 years 4 days	5 years 8 months 27 days
Interest Rate Contracts [Member] | Options [Member] | Purchased [Member]
Derivative [Line Items]
Notional Value, Assets	$ 10,127	$ 8,705
Fair Value, Assets	$ 7	$ 10
Derivative Asset Average Remaining Maturity Period	2 years 1 month 10 days	2 years 7 months 10 days
Notional Value, Liabilities	$ 356	$ 146
Fair Value, Liabilities	$ 26	$ 1
Derivative Liability Average Remaining Maturity Period	10 months 21 days	2 years 2 months 23 days
Interest Rate Contracts [Member] | Options [Member] | Written [Member]
Derivative [Line Items]
Notional Value, Assets	$ 449	$ 146
Fair Value, Assets	$ 27	$ 2
Derivative Asset Average Remaining Maturity Period	5 years 5 months 19 days	2 years 2 months 23 days
Notional Value, Liabilities	$ 8,987	$ 8,482
Fair Value, Liabilities	$ 3	$ 9
Derivative Liability Average Remaining Maturity Period	1 year 8 months 1 day	2 years 6 months 26 days
Interest Rate Contracts [Member] | Futures [Member] | Purchased [Member]
Derivative [Line Items]
Notional Value, Assets	$ 3,540
Fair Value, Assets	$ 1
Derivative Asset Average Remaining Maturity Period	1 year 4 months 28 days
Notional Value, Liabilities	$ 4,701	$ 2,859
Fair Value, Liabilities		$ 2
Derivative Liability Average Remaining Maturity Period	9 months 26 days	10 months 2 days
Interest Rate Contracts [Member] | Futures [Member] | Written [Member]
Derivative [Line Items]
Notional Value, Assets		$ 45
Derivative Asset Average Remaining Maturity Period		11 months 19 days
Foreign Exchange Rate Contracts [Member] | Forwards, Spots and Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	$ 24,249	$ 18,399
Fair Value, Assets	$ 690	$ 851
Derivative Asset Average Remaining Maturity Period	6 months 7 days	7 months 2 days
Notional Value, Liabilities	$ 18,252	$ 17,959
Fair Value, Liabilities	$ 663	$ 830
Derivative Liability Average Remaining Maturity Period	7 months 24 days	6 months 29 days
Foreign Exchange Option [Member] | Purchased [Member]
Derivative [Line Items]
Notional Value, Assets	$ 1,771	$ 1,485
Fair Value, Assets	$ 47	$ 43
Derivative Asset Average Remaining Maturity Period	1 year 2 months 23 days	1 year 2 months 9 days
Foreign Exchange Option [Member] | Written [Member]
Derivative [Line Items]
Notional Value, Liabilities	$ 1,771	$ 1,485
Fair Value, Liabilities	$ 47	$ 43
Derivative Liability Average Remaining Maturity Period	1 year 2 months 23 days	1 year 2 months 9 days