Debt Securities (Investments in Debt Securities by Contractual Maturity) (Detail) - USD ($) $ in Millions	Sep. 30, 2022	Dec. 31, 2021
Schedule Of Available For Sale Securities [Line Items]
Debt Securities, Amortized cost	$ 9,314	$ 9,317
Debt securities, Estimated fair value	8,153	9,362
Amortized cost	5,355
U.S. Treasury bonds
Schedule Of Available For Sale Securities [Line Items]
Amortized cost, Due in one year or less	117
Amortized cost, Due after one through five years	56
Amortized cost, Due after five through ten years	10
Amortized cost, Due after ten years	13
Debt Securities, Amortized cost	196	123
Estimated fair value, Due in one year or less	117
Estimated fair value, Due after one through five years	50
Estimated fair value, Due after five through ten years	8
Estimated fair value, Due after ten years	11
Debt securities, Estimated fair value	186	123
Municipal bonds
Schedule Of Available For Sale Securities [Line Items]
Amortized cost, Due in one year or less	21
Amortized cost, Due after one through five years	229
Amortized cost, Due after five through ten years	805
Amortized cost, Due after ten years	609
Debt Securities, Amortized cost	1,664	1,607
Estimated fair value, Due in one year or less	21
Estimated fair value, Due after one through five years	214
Estimated fair value, Due after five through ten years	699
Estimated fair value, Due after ten years	509
Debt securities, Estimated fair value	1,443	1,649
Foreign government bonds
Schedule Of Available For Sale Securities [Line Items]
Amortized cost, Due in one year or less	28
Amortized cost, Due after one through five years	111
Amortized cost, Due after five through ten years	73
Amortized cost, Due after ten years	12
Debt Securities, Amortized cost	224	228
Estimated fair value, Due in one year or less	28
Estimated fair value, Due after one through five years	108
Estimated fair value, Due after five through ten years	63
Estimated fair value, Due after ten years	8
Debt securities, Estimated fair value	207	227
Governmental agency bonds
Schedule Of Available For Sale Securities [Line Items]
Amortized cost, Due in one year or less	1
Amortized cost, Due after one through five years	189
Amortized cost, Due after five through ten years	7
Amortized cost, Due after ten years	59
Debt Securities, Amortized cost	256	175
Estimated fair value, Due in one year or less	1
Estimated fair value, Due after one through five years	182
Estimated fair value, Due after five through ten years	6
Estimated fair value, Due after ten years	48
Debt securities, Estimated fair value	237	177
U.S. corporate debt securities
Schedule Of Available For Sale Securities [Line Items]
Amortized cost, Due in one year or less	60
Amortized cost, Due after one through five years	694
Amortized cost, Due after five through ten years	275
Amortized cost, Due after ten years	86
Debt Securities, Amortized cost	1,115	1,071
Estimated fair value, Due in one year or less	60
Estimated fair value, Due after one through five years	627
Estimated fair value, Due after five through ten years	240
Estimated fair value, Due after ten years	64
Debt securities, Estimated fair value	991	1,081
Foreign corporate debt securities
Schedule Of Available For Sale Securities [Line Items]
Amortized cost, Due in one year or less	36
Amortized cost, Due after one through five years	306
Amortized cost, Due after five through ten years	111
Amortized cost, Due after ten years	51
Debt Securities, Amortized cost	504	493
Estimated fair value, Due in one year or less	35
Estimated fair value, Due after one through five years	278
Estimated fair value, Due after five through ten years	95
Estimated fair value, Due after ten years	39
Debt securities, Estimated fair value	447	$ 498
Aggregate Debt Securities Excluding Mortgage Backed And Asset Backed Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized cost, Due in one year or less	263
Amortized cost, Due after one through five years	1,585
Amortized cost, Due after five through ten years	1,281
Amortized cost, Due after ten years	830
Debt Securities, Amortized cost	3,959
Estimated fair value, Due in one year or less	262
Estimated fair value, Due after one through five years	1,459
Estimated fair value, Due after five through ten years	1,111
Estimated fair value, Due after ten years	679
Debt securities, Estimated fair value	3,511
Collateralized Mortgage-Backed Securities
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value	$ 4,642