Fair Value (Level 3 Total Realized And Unrealized Gains And Losses Recorded In Revenue) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Trading Services [Member]
Realized and Unrealized Gains and Losses [Line Items]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Gain (Loss) Included in Trading Revenue	$ (11)	$ 12	$ 5	$ 1
Fair Value, Assets and Liabilities Measured on Recurring Basis, Change in Unrealized Gain (Loss) Included in Trading Revenue	(4)		(1)	7
Total Fee Revenue [Member]
Realized and Unrealized Gains and Losses [Line Items]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Gain (Loss) Included in Trading Revenue	(11)	12	5	1
Fair Value, Assets and Liabilities Measured on Recurring Basis, Change in Unrealized Gain (Loss) Included in Trading Revenue	(4)		(1)	7
Interest Income [Member]
Realized and Unrealized Gains and Losses [Line Items]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Gain (Loss) Included in Trading Revenue	181	37	407	391
Fair Value, Assets and Liabilities Measured on Recurring Basis, Change in Unrealized Gain (Loss) Included in Trading Revenue			0	0
Total Revenue [Member]
Realized and Unrealized Gains and Losses [Line Items]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Gain (Loss) Included in Trading Revenue	170	49	412	392
Fair Value, Assets and Liabilities Measured on Recurring Basis, Change in Unrealized Gain (Loss) Included in Trading Revenue	$ (4)	$ 0	$ (1)	$ 7