Investments (Fair Value of Available-For-Sale Investments with Gross Unrealized Losses by Investment Type and Length of Time That Individual Securities Have Been in a Continuous Unrealized Loss Position) (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Debt Securities - held-to-maturity
Schedule of Investments [Line Items]
Less Than 12 Months, Fair Value	$ 17,118	$ 2,415
Less Than 12 Months, Gross Unrealized Losses	(237)	(16)
Greater Than 12 Months, Fair Value	886	549
Greater Than 12 Months, Gross Unrealized Losses	(37)	(6)
Total, Fair Value	18,004	2,964
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(274)	(22)
U.S. Government and Agency Obligations [Member]
Schedule of Investments [Line Items]
Less Than 12 Months, Fair Value	1,976	346
Less Than 12 Months, Gross Unrealized Losses	(18)	(3)
Greater Than 12 Months, Fair Value	249
Greater Than 12 Months, Gross Unrealized Losses	(13)
Total, Fair Value	2,225	346
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(31)	(3)
State and Municipal Obligations [Member]
Schedule of Investments [Line Items]
Less Than 12 Months, Fair Value	1,386
Less Than 12 Months, Gross Unrealized Losses	(19)
Greater Than 12 Months, Fair Value	31
Greater Than 12 Months, Gross Unrealized Losses	(1)
Total, Fair Value	1,417
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(20)
Corporate Obligations [Member]
Schedule of Investments [Line Items]
Less Than 12 Months, Fair Value	9,357	1,273
Less Than 12 Months, Gross Unrealized Losses	(130)	(9)
Greater Than 12 Months, Fair Value	376	456
Greater Than 12 Months, Gross Unrealized Losses	(15)	(3)
Total, Fair Value	9,733	1,729
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(145)	(12)
U.S. Agency Mortgage-Backed Securities [Member]
Schedule of Investments [Line Items]
Less Than 12 Months, Fair Value	3,078	601
Less Than 12 Months, Gross Unrealized Losses	(52)	(3)
Greater Than 12 Months, Fair Value	116	0
Greater Than 12 Months, Gross Unrealized Losses	(3)	0
Total, Fair Value	3,194	601
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(55)	(3)
Non-U.S. Agency Mortgage-Backed Securities [Member]
Schedule of Investments [Line Items]
Less Than 12 Months, Fair Value	1,321	195
Less Than 12 Months, Gross Unrealized Losses	(18)	(1)
Greater Than 12 Months, Fair Value	114	93
Greater Than 12 Months, Gross Unrealized Losses	(5)	(3)
Total, Fair Value	1,435	288
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ (23)	$ (4)