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Debt Securities (Investments in Debt Securities, Classified as Available-For-Sale) (Detail) - USD ($)
$ in Millions
Jun. 30, 2022
Dec. 31, 2021
Schedule Of Available For Sale Securities [Line Items]    
Debt Securities, Amortized cost $ 9,257 $ 9,317
Debt Securities, Gross unrealized gains 5 127
Debt Securities, Gross unrealized losses (812) (82)
Debt securities, Estimated fair value 8,450 9,362
U.S. Treasury bonds    
Schedule Of Available For Sale Securities [Line Items]    
Debt Securities, Amortized cost 155 123
Debt Securities, Gross unrealized gains 0 1
Debt Securities, Gross unrealized losses (8) (1)
Debt securities, Estimated fair value 147 123
Municipal bonds    
Schedule Of Available For Sale Securities [Line Items]    
Debt Securities, Amortized cost 1,609 1,607
Debt Securities, Gross unrealized gains 2 59
Debt Securities, Gross unrealized losses (149) (17)
Debt securities, Estimated fair value 1,462 1,649
Foreign government bonds    
Schedule Of Available For Sale Securities [Line Items]    
Debt Securities, Amortized cost 217 228
Debt Securities, Gross unrealized gains 0 2
Debt Securities, Gross unrealized losses (17) (3)
Debt securities, Estimated fair value 200 227
Governmental agency bonds    
Schedule Of Available For Sale Securities [Line Items]    
Debt Securities, Amortized cost 141 175
Debt Securities, Gross unrealized gains 0 3
Debt Securities, Gross unrealized losses (12) (1)
Debt securities, Estimated fair value 129 177
Governmental agency mortgage-backed securities    
Schedule Of Available For Sale Securities [Line Items]    
Debt Securities, Amortized cost 5,539 5,620
Debt Securities, Gross unrealized gains 3 34
Debt Securities, Gross unrealized losses (492) (47)
Debt securities, Estimated fair value 5,050 5,607
U.S. corporate debt securities    
Schedule Of Available For Sale Securities [Line Items]    
Debt Securities, Amortized cost 1,096 1,071
Debt Securities, Gross unrealized gains 0 19
Debt Securities, Gross unrealized losses (93) (9)
Debt securities, Estimated fair value 1,003 1,081
Foreign corporate debt securities    
Schedule Of Available For Sale Securities [Line Items]    
Debt Securities, Amortized cost 500 493
Debt Securities, Gross unrealized gains 0 9
Debt Securities, Gross unrealized losses (41) (4)
Debt securities, Estimated fair value $ 459 $ 498