Gains and Losses Recognized in Income from Trading Securities (Parenthetical) (Detail) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Gross realized gains on trading securities	[1]	$ 1	$ 4	$ 4	$ 6
Gross realized losses on trading securities	[2]	(2)	(1)	(7)	(4)
Trading Securities, Change in Unrealized Holding Gain (Loss)	[3]	(3)	(4)	(4)	(2)
Corporate Banking Revenue [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Gross realized gains on trading securities		1	3	1	2
Gross realized losses on trading securities		$ (2)	$ (7)	$ (1)	$ (4)

[1] Includes realized gains of $1 and $3 for the three and nine months ended September 30, 2015, respectively, and $1 and $2 for the three and nine months ended September 30, 2014, respectively, recorded in corporate banking revenue in the Condensed Consolidated Statements of Income.

[2] Includes realized losses of $2 and $7 for the three and nine months ended September 30, 2015, respectively, and $1 and $4 for the three and nine months ended September 30, 2014, respectively, recorded in corporate banking revenue in the Condensed Consolidated Statements of Income.

[3] Includes an immaterial amount of net unrealized gains for both the three and nine months ended September 30, 2015 recorded in corporate banking revenue in the Condensed Consolidated Statements of Income. Includes an immaterial amount of net unrealized losses for the three months ended September 30, 2014 and an immaterial amount of net unrealized gains for the nine months ended September 30, 2014 recorded in corporate banking revenue in the Condensed Consolidated Statements of Income.