Asset Quality - Changes in Outstanding Unpaid Principal Balance, Carrying Amount, and Accretable Yield for PCI Loans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Carrying Amount
Outstanding Unpaid Principal Balance	$ 865	$ 11
Purchase Credit Impaired Loans [Member]
Accretable Yield
Balance at beginning of period	5	5	$ 5
Additions	205	0	0
Accretion	(29)	(1)	(2)
Net reclassifications from non-accretable to accretable	35	1	2
Payments received, net	(19)	0	0
Disposals	0	0	0
Balance at end of period	197	5	5
Carrying Amount
Balance at beginning of period	11	13	16
Balance at end of period	865	11	13
Outstanding Unpaid Principal Balance	$ 1,002	$ 17	$ 20	$ 24