Investment Securities (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale [Line Items]
Accrued interest available-for-sale debt securities	$ 7	$ 12
Available-for-sale debt securities:
Cost	4,010
Estimated Fair Value	4,003
Equity securities
Cost	61	66
Gross Unrealized Gains	1	17
Gross Unrealized Losses	(7)	(4)
Estimated Fair Value	55	79
Total Cost	4,071	2,548
Total Gross Unrealized Gains	11	48
Total Gross Unrealized Losses	(24)	(5)
Total Estimated Fair Value	4,058	2,591
State and municipal obligations
Available-for-sale debt securities:
Cost	74	106
Gross Unrealized Gains	2	5
Gross Unrealized Losses	(4)	0
Estimated Fair Value	72	111
U.S. Government agency obligations
Available-for-sale debt securities:
Cost	6	6
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	6	6
U.S. Government treasury obligations
Available-for-sale debt securities:
Cost	3,240	1,680
Gross Unrealized Gains	7	25
Gross Unrealized Losses	(12)	(1)
Estimated Fair Value	3,235	1,704
Mortgage-backed securities
Available-for-sale debt securities:
Cost	15	17
Gross Unrealized Gains	1	1
Gross Unrealized Losses	0	0
Estimated Fair Value	16	18
Foreign government bonds and obligations
Available-for-sale debt securities:
Cost	636	630
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1)	0
Estimated Fair Value	635	630
Other
Available-for-sale debt securities:
Cost	39	43
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	$ 39	$ 43