Investment Securities - Amortized Cost and Estimated Fair Value of Securities by Contractual Maturity (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Amortized Cost
Due in one year or less	$ 3
Due after one year through five years	20
Due after five years through 10 years	93
Due after 10 years	1,999
Amortized Cost	2,115	$ 2,206
Fair Value
Due in one year or less	3
Due after one year through five years	20
Due after five years through 10 years	95
Due after 10 years	1,998
Fair Value	$ 2,116	2,142
Weighted-Average Yield
Due in one year or less (in percentage)	2.12%
Due after one year through five years (in percentage)	4.07%
Due after five years through 10 years (in percentage)	4.23%
Due after 10 years (in percentage)	2.41%
Amortized Cost
Due in one year or less	$ 0
Due after one year through five years	10
Due after five years through 10 years	9
Due after 10 years	579
Amortized Cost	598	703
Fair Value
Due in one year or less	0
Due after one year through five years	10
Due after five years through 10 years	9
Due after 10 years	580
Fair value	$ 599	$ 681
Weighted-Average Yield
Due in one year or less (in percentage)	0.00%
Due after one year through five years (in percentage)	2.48%
Due after five years through 10 years (in percentage)	2.29%
Due after 10 years (in percentage)	2.42%