Investment Securities (Contractual Maturity) (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Investment Securities Available-for-Sale, Amortized Cost
Due after one year through five years, amortized cost	$ 16
Due after five years through 10 years, amortized cost	35
Due after 10 years, amortized cost	1,577
Total, amortized cost	1,628
Investment Securities Available-for-Sale, Estimated Fair Value
Due after one year through five years, fair value	16
Due after five years through 10 years, fair value	35
Due after 10 years, fair value	1,563
Fair Value	$ 1,614	$ 1,480
Investment Securities Available-for-Sale, Weighted-Average Yield
Due after one year through five years, weighted average yield (as a percent)	3.39%
Due after five years through 10 years, weighted average yield (as a percent)	5.18%
Due after 10 years, weighted average yield (as a percent)	2.30%
Investment Securities Held-to-maturity, Amortized cost
Due after one year through five years, amortized cost	$ 0
Due after five years through 10 years, amortized cost	61
Due after 10 years, amortized cost	953
Amortized Cost	1,014	1,093
Investment Securities Held-to-maturity, Estimated Fair Value
Due after one year through five years, fair value	0
Due after five years through 10 years, fair value	61
Due after 10 years, fair value	947
Fair Value	$ 1,008	$ 1,084
Investment Securities Held-to-maturity, Weighted-Average Yield
Due after one year through five years, weighted average yield (as a percent)	0.00%
Due after five years through 10 years, weighted average yield (as a percent)	2.50%
Due after 10 years, weighted average yield (as a percent)	2.45%