Investment Securities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Available-for-sale debt securities:
Estimated Fair Value	$ 2,512	$ 21,550
Equity securities
Cost	66	56
Gross Unrealized Gains	17	27
Gross Unrealized Losses	(4)	(2)
Estimated Fair Value	79	81
Total Cost	2,548	21,521
Total Gross Unrealized Gains	48	112
Total Gross Unrealized Losses	(5)	(2)
Total Estimated Fair Value	2,591	21,631
State and municipal obligations
Available-for-sale debt securities:
Cost	106	172
Gross Unrealized Gains	5	7
Gross Unrealized Losses	0	0
Estimated Fair Value	111	179
U.S. Government agency obligations
Available-for-sale debt securities:
Cost	6	7
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	6	7
U.S. Government treasury obligations
Available-for-sale debt securities:
Cost	1,680	20,655
Gross Unrealized Gains	25	76
Gross Unrealized Losses	(1)	0
Estimated Fair Value	1,704	20,731
Mortgage-backed securities
Available-for-sale debt securities:
Cost	17	28
Gross Unrealized Gains	1	2
Gross Unrealized Losses	0	0
Estimated Fair Value	18	30
Foreign government bonds and obligations
Available-for-sale debt securities:
Cost	630	581
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	630	581
Other
Available-for-sale debt securities:
Cost	43	22
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	$ 43	$ 22