Securities - Changes in Credit Loss (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Changes in the credit loss component of credit-impaired debt securities, securities with no intent to sell [Abstract]
Balance, beginning of period	$ 3	$ 1	$ 522
Additions:
Newly credit-impaired securities	1	2	1
Losses reclassified from other comprehensive income on previously credit-impaired securities	0	0	0
Reductions:
Sales and redemptions of credit-impaired securities	0	0	(522)
Balance, end of period	$ 4	$ 3	$ 1