Securities - Changes in Credit Loss (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Changes in the credit loss component of credit-impaired debt securities, securities with no intent to sell [Abstract]
Balance, beginning of period	$ 4	$ 1	$ 3	$ 1
Additions:
Newly credit-impaired securities	0	0	1	0
Balance, end of period	$ 4	$ 1	$ 4	$ 1