Investment Securities - Amortized Cost and Estimated Fair Value of Securities by Contractual Maturity (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Investment Securities Available-for-Sale, Amortized Cost
Due in one year or less	$ 6
Due after one year through five years	10
Due after five years through 10 years	106
Due after 10 years	1,655
Amortized Cost	1,777	$ 1,870
Investment Securities Available-for-Sale, Fair Value
Due in one year or less	6
Due after one year through five years	11
Due after five years through 10 years	111
Due after 10 years	1,695
Fair Value	$ 1,823	1,944
Investment Securities Available-for-Sale, Weighted Average Yield
Due in one year or less (as a percent)	2.25%
Due after one year through five years (as a percent)	3.81%
Due after five years through 10 years (as a percent)	3.88%
Due after 10 years (as a percent)	2.20%
Investment Securities Held-to-maturity, Amortized cost
Due in one year or less	$ 0
Due after one year through five years	10
Due after five years through 10 years	4
Due after 10 years	256
Amortized Cost	270	377
Investment Securities Held-to-maturity, Fair Value
Due in one year or less	0
Due after one year through five years	10
Due after five years through 10 years	4
Due after 10 years	266
Fair Value	$ 280	$ 393
Investment Securities Held-to-maturity, Weighted Average Yield
Due in one year or less (as a percent)	0.00%
Due after one year through five years (as a percent)	2.53%
Due after five years through 10 years (as a percent)	1.99%
Due after 10 years (as a percent)	2.47%