Investment Securities (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Accrued interest available-for-sale debt securities	$ 21	$ 26
Available-for-sale debt securities:
Cost	12,336
Estimated Fair Value	12,392
Equity securities
Cost	52	56
Gross Unrealized Gains	1	27
Gross Unrealized Losses	(2)	(2)
Estimated Fair Value	51	81
Total Cost	12,388	21,521
Total Gross Unrealized Gains	58	112
Total Gross Unrealized Losses	(3)	(2)
Total Estimated Fair Value	12,443	21,631
State and municipal obligations
Available-for-sale debt securities:
Cost	133	172
Gross Unrealized Gains	6	7
Gross Unrealized Losses	(1)	0
Estimated Fair Value	138	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	11,397	20,655
Gross Unrealized Gains	49	76
Gross Unrealized Losses	0	0
Estimated Fair Value	11,446	20,731
Mortgage-backed securities
Available-for-sale debt securities:
Cost	22	28
Gross Unrealized Gains	2	2
Gross Unrealized Losses	0	0
Estimated Fair Value	24	30
Foreign government bonds and obligations
Available-for-sale debt securities:
Cost	741	581
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	741	581
Other Debt Securities
Available-for-sale debt securities:
Cost	37	22
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	$ 37	$ 22