Securities - Schedule of Credit Losses with OTTI (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Balance at beginning of period	$ 42	$ 64
Reductions for securities sold/settled during the period	(23)	(2)
Credit recoveries through yield	(1)	(1)
Balance at end of period	$ 18	$ 61