Fair Value - Level 3 Total Realized And Unrealized Gains And Losses Recorded In Revenue (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Total revenue
Realized and Unrealized Gains and Losses [Line Items]
Total realized and unrealized gains (losses) recorded in revenue	$ 5	$ 35
Change in unrealized gains (losses) related to financial instruments held	0	14
Trading services
Realized and Unrealized Gains and Losses [Line Items]
Total realized and unrealized gains (losses) recorded in revenue	(2)	22
Change in unrealized gains (losses) related to financial instruments held	0	14
Total fee revenue
Realized and Unrealized Gains and Losses [Line Items]
Total realized and unrealized gains (losses) recorded in revenue	(2)	22
Change in unrealized gains (losses) related to financial instruments held	0	14
Net interest revenue
Realized and Unrealized Gains and Losses [Line Items]
Total realized and unrealized gains (losses) recorded in revenue	7	13
Change in unrealized gains (losses) related to financial instruments held	$ 0	$ 0