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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
Mar. 31, 2025
Dec. 31, 2024
Debt Securities [Member]    
Schedule of Investments [Line Items]    
Less Than 12 Months, Fair Value $ 15,095 $ 16,677
Less Than 12 Months, Gross Unrealized Losses (359) (518)
Greater Than 12 Months, Fair Value 23,204 24,223
Greater Than 12 Months, Gross Unrealized Losses (2,104) (2,440)
Total, Fair Value 38,299 40,900
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss (2,463) (2,958)
U.S. Government and Agency Obligations [Member]    
Schedule of Investments [Line Items]    
Less Than 12 Months, Fair Value 1,540 1,475
Less Than 12 Months, Gross Unrealized Losses (28) (51)
Greater Than 12 Months, Fair Value 1,944 2,152
Greater Than 12 Months, Gross Unrealized Losses (184) (223)
Total, Fair Value 3,484 3,627
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss (212) (274)
State and Municipal Obligations [Member]    
Schedule of Investments [Line Items]    
Less Than 12 Months, Fair Value 2,111 2,593
Less Than 12 Months, Gross Unrealized Losses (67) (58)
Greater Than 12 Months, Fair Value 4,150 4,085
Greater Than 12 Months, Gross Unrealized Losses (300) (317)
Total, Fair Value 6,261 6,678
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss (367) (375)
Corporate Obligations [Member]    
Schedule of Investments [Line Items]    
Less Than 12 Months, Fair Value 6,855 7,402
Less Than 12 Months, Gross Unrealized Losses (146) (213)
Greater Than 12 Months, Fair Value 10,705 11,449
Greater Than 12 Months, Gross Unrealized Losses (778) (927)
Total, Fair Value 17,560 18,851
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss (924) (1,140)
U.S. Agency Mortgage-Backed Securities [Member]    
Schedule of Investments [Line Items]    
Less Than 12 Months, Fair Value 4,032 4,791
Less Than 12 Months, Gross Unrealized Losses (114) (191)
Greater Than 12 Months, Fair Value 4,660 4,674
Greater Than 12 Months, Gross Unrealized Losses (698) (803)
Total, Fair Value 8,692 9,465
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss (812) (994)
Non-U.S. Agency Mortgage-Backed Securities [Member]    
Schedule of Investments [Line Items]    
Less Than 12 Months, Fair Value 557 416
Less Than 12 Months, Gross Unrealized Losses (4) (5)
Greater Than 12 Months, Fair Value 1,745 1,863
Greater Than 12 Months, Gross Unrealized Losses (144) (170)
Total, Fair Value 2,302 2,279
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss $ (148) $ (175)