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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, 2023
Dec. 31, 2022
Debt Securities [Member]    
Schedule of Investments [Line Items]    
Less Than 12 Months, Fair Value $ 11,886 $ 24,899
Less Than 12 Months, Gross Unrealized Losses (301) (1,750)
Greater Than 12 Months, Fair Value 23,641 12,320
Greater Than 12 Months, Gross Unrealized Losses (2,816) (1,914)
Total, Fair Value 35,527 37,219
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss (3,117) (3,664)
U.S. Government and Agency Obligations [Member]    
Schedule of Investments [Line Items]    
Less Than 12 Months, Fair Value 1,279 2,007
Less Than 12 Months, Gross Unrealized Losses (12) (96)
Greater Than 12 Months, Fair Value 1,825 1,290
Greater Than 12 Months, Gross Unrealized Losses (224) (189)
Total, Fair Value 3,104 3,297
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss (236) (285)
State and Municipal Obligations [Member]    
Schedule of Investments [Line Items]    
Less Than 12 Months, Fair Value 1,898 4,630
Less Than 12 Months, Gross Unrealized Losses (30) (288)
Greater Than 12 Months, Fair Value 3,110 1,178
Greater Than 12 Months, Gross Unrealized Losses (335) (191)
Total, Fair Value 5,008 5,808
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss (365) (479)
Corporate Obligations [Member]    
Schedule of Investments [Line Items]    
Less Than 12 Months, Fair Value 6,337 13,003
Less Than 12 Months, Gross Unrealized Losses (178) (893)
Greater Than 12 Months, Fair Value 12,443 6,637
Greater Than 12 Months, Gross Unrealized Losses (1,347) (905)
Total, Fair Value 18,780 19,640
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss (1,525) (1,798)
U.S. Agency Mortgage-Backed Securities [Member]    
Schedule of Investments [Line Items]    
Less Than 12 Months, Fair Value 1,589 3,561
Less Than 12 Months, Gross Unrealized Losses (55) (345)
Greater Than 12 Months, Fair Value 4,274 2,239
Greater Than 12 Months, Gross Unrealized Losses (653) (463)
Total, Fair Value 5,863 5,800
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss (708) (808)
Non-U.S. Agency Mortgage-Backed Securities [Member]    
Schedule of Investments [Line Items]    
Less Than 12 Months, Fair Value 783 1,698
Less Than 12 Months, Gross Unrealized Losses (26) (128)
Greater Than 12 Months, Fair Value 1,989 976
Greater Than 12 Months, Gross Unrealized Losses (257) (166)
Total, Fair Value 2,772 2,674
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss $ (283) $ (294)