Derivative Financial Instruments (Summary of recognized gains (losses) related to derivative financial instruments) (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
Recognized Gains (Losses)
Derivative instruments not designated as hedging instruments, gain (loss), net	$ (1)	$ 1	$ (1)
Derivative instruments, gain (loss) recognized in income, net	(2)	1	(1)
Currency forwards [Member]
Recognized Gains (Losses)
Derivative instruments not designated as hedging instruments, gain (loss), net	(1)		(1)	(1)
Forward commitments for mortgage-backed securities [Member]
Recognized Gains (Losses)
Derivative instruments not designated as hedging instruments, gain (loss), net		1		1
Futures sold, not yet purchased [Member]
Recognized Gains (Losses)
Gain (loss) on derivative instruments held for trading purposes, net	$ (1)