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	Sep. 30, 2024	Dec. 31, 2023
Debt Securities [Member]
Schedule of Investments [Line Items]
Less Than 12 Months, Fair Value	$ 7,397	$ 5,619
Less Than 12 Months, Gross Unrealized Losses	(52)	(49)
Greater Than 12 Months, Fair Value	25,908	28,107
Greater Than 12 Months, Gross Unrealized Losses	(1,921)	(2,641)
Total, Fair Value	33,305	33,726
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(1,973)	(2,690)
U.S. Government and Agency Obligations [Member]
Schedule of Investments [Line Items]
Less Than 12 Months, Fair Value	894	1,270
Less Than 12 Months, Gross Unrealized Losses	(7)	(7)
Greater Than 12 Months, Fair Value	2,448	2,077
Greater Than 12 Months, Gross Unrealized Losses	(175)	(227)
Total, Fair Value	3,342	3,347
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(182)	(234)
State and Municipal Obligations [Member]
Schedule of Investments [Line Items]
Less Than 12 Months, Fair Value	726	907
Less Than 12 Months, Gross Unrealized Losses	(6)	(7)
Greater Than 12 Months, Fair Value	4,278	4,063
Greater Than 12 Months, Gross Unrealized Losses	(250)	(315)
Total, Fair Value	5,004	4,970
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(256)	(322)
Corporate Obligations [Member]
Schedule of Investments [Line Items]
Less Than 12 Months, Fair Value	3,499	1,826
Less Than 12 Months, Gross Unrealized Losses	(18)	(17)
Greater Than 12 Months, Fair Value	12,174	14,696
Greater Than 12 Months, Gross Unrealized Losses	(763)	(1,169)
Total, Fair Value	15,673	16,522
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(781)	(1,186)
U.S. Agency Mortgage-Backed Securities [Member]
Schedule of Investments [Line Items]
Less Than 12 Months, Fair Value	2,140	1,337
Less Than 12 Months, Gross Unrealized Losses	(20)	(12)
Greater Than 12 Months, Fair Value	5,018	5,069
Greater Than 12 Months, Gross Unrealized Losses	(580)	(696)
Total, Fair Value	7,158	6,406
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(600)	(708)
Non-U.S. Agency Mortgage-Backed Securities [Member]
Schedule of Investments [Line Items]
Less Than 12 Months, Fair Value	138	279
Less Than 12 Months, Gross Unrealized Losses	(1)	(6)
Greater Than 12 Months, Fair Value	1,990	2,202
Greater Than 12 Months, Gross Unrealized Losses	(153)	(234)
Total, Fair Value	2,128	2,481
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ (154)	$ (240)