Derivative Instruments - Customer-Related Derivative Positions of Company (Detail) - Customer-Related Positions [Member] - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Derivative [Line Items]
Notional Value, Assets	$ 74,162	$ 50,780
Fair Value, Assets	2,436	1,853
Notional Value, Liabilities	69,179	47,993
Fair Value, Liabilities	2,447	1,717
Interest Rate Contracts [Member] | Receive Fixed/Pay Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	39,413	21,724
Fair Value, Assets	$ 1,395	$ 888
Derivative Asset Average Remaining Maturity Period	5 years 3 months 15 days	6 years 1 month 2 days
Notional Value, Liabilities	$ 2,325	$ 5,880
Fair Value, Liabilities	$ 6	$ 24
Derivative Liability Average Remaining Maturity Period	7 years 1 month 10 days	3 years 9 months 15 days
Interest Rate Contracts [Member] | Pay Fixed/Receive Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	$ 1,560	$ 4,622
Fair Value, Assets	$ 4	$ 26
Derivative Asset Average Remaining Maturity Period	7 years 3 months 11 days	3 years 3 months 7 days
Notional Value, Liabilities	$ 38,952	$ 21,821
Fair Value, Liabilities	$ 1,458	$ 892
Derivative Liability Average Remaining Maturity Period	5 years 4 months 10 days	6 years 29 days
Interest Rate Contracts [Member] | Options [Member] | Purchased [Member]
Derivative [Line Items]
Notional Value, Assets	$ 7,642	$ 4,409
Fair Value, Assets	$ 8	$ 10
Derivative Asset Average Remaining Maturity Period	2 years 3 months 22 days	3 years 9 months 15 days
Notional Value, Liabilities	$ 386	$ 24
Fair Value, Liabilities	$ 3
Derivative Liability Average Remaining Maturity Period	17 years 2 months 16 days	2 years 5 months 1 day
Interest Rate Contracts [Member] | Options [Member] | Written [Member]
Derivative [Line Items]
Notional Value, Assets	$ 147	$ 24
Fair Value, Assets	$ 4
Derivative Asset Average Remaining Maturity Period	2 years 5 months 23 days	2 years 5 months 1 day
Notional Value, Liabilities	$ 7,658	$ 4,375
Fair Value, Liabilities	$ 7	$ 10
Derivative Liability Average Remaining Maturity Period	2 years 11 months 27 days	3 years 9 months 15 days
Interest Rate Contracts [Member] | Futures [Member] | Purchased [Member]
Derivative [Line Items]
Notional Value, Assets	$ 2,933	$ 1,811
Fair Value, Assets	$ 2
Derivative Asset Average Remaining Maturity Period	1 year 15 days	2 months 19 days
Notional Value, Liabilities		$ 226
Derivative Liability Average Remaining Maturity Period		5 months 12 days
Interest Rate Contracts [Member] | Futures [Member] | Written [Member]
Derivative [Line Items]
Notional Value, Assets		$ 152
Derivative Asset Average Remaining Maturity Period		1 year 29 days
Notional Value, Liabilities	$ 87	$ 46
Derivative Liability Average Remaining Maturity Period	1 year 2 months 19 days	1 year 8 months 23 days
Foreign Exchange Rate Contracts [Member] | Forwards, Spots and Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	$ 21,126	$ 17,062
Fair Value, Assets	$ 980	$ 890
Derivative Asset Average Remaining Maturity Period	6 months 11 days	6 months 7 days
Notional Value, Liabilities	$ 18,430	$ 14,645
Fair Value, Liabilities	$ 930	$ 752
Derivative Liability Average Remaining Maturity Period	7 months 6 days	7 months 2 days
Foreign Exchange Option [Member] | Purchased [Member]
Derivative [Line Items]
Notional Value, Assets	$ 1,341	$ 976
Fair Value, Assets	$ 43	$ 39
Derivative Asset Average Remaining Maturity Period	1 year 4 months 28 days	5 months 9 days
Foreign Exchange Option [Member] | Written [Member]
Derivative [Line Items]
Notional Value, Liabilities	$ 1,341	$ 976
Fair Value, Liabilities	$ 43	$ 39
Derivative Liability Average Remaining Maturity Period	1 year 4 months 28 days	5 months 9 days