Debt Securities (Investments in Debt Securities, Classified as Available-For-Sale) (Detail) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Schedule Of Available For Sale Securities [Line Items]
Debt Securities, Amortized cost	$ 9,388	$ 9,317
Debt Securities, Gross unrealized gains	29	127
Debt Securities, Gross unrealized losses	(480)	(82)
Debt securities, Estimated fair value	8,937	9,362
U.S. Treasury bonds
Schedule Of Available For Sale Securities [Line Items]
Debt Securities, Amortized cost	94	123
Debt Securities, Gross unrealized gains	0	1
Debt Securities, Gross unrealized losses	(6)	(1)
Debt securities, Estimated fair value	88	123
Municipal bonds
Schedule Of Available For Sale Securities [Line Items]
Debt Securities, Amortized cost	1,596	1,607
Debt Securities, Gross unrealized gains	12	59
Debt Securities, Gross unrealized losses	(87)	(17)
Debt securities, Estimated fair value	1,521	1,649
Foreign government bonds
Schedule Of Available For Sale Securities [Line Items]
Debt Securities, Amortized cost	235	228
Debt Securities, Gross unrealized gains	0	2
Debt Securities, Gross unrealized losses	(12)	(3)
Debt securities, Estimated fair value	223	227
Governmental agency bonds
Schedule Of Available For Sale Securities [Line Items]
Debt Securities, Amortized cost	153	175
Debt Securities, Gross unrealized gains	0	3
Debt Securities, Gross unrealized losses	(6)	(1)
Debt securities, Estimated fair value	147	177
Governmental agency mortgage-backed securities
Schedule Of Available For Sale Securities [Line Items]
Debt Securities, Amortized cost	5,668	5,620
Debt Securities, Gross unrealized gains	11	34
Debt Securities, Gross unrealized losses	(298)	(47)
Debt securities, Estimated fair value	5,381	5,607
U.S. corporate debt securities
Schedule Of Available For Sale Securities [Line Items]
Debt Securities, Amortized cost	1,141	1,071
Debt Securities, Gross unrealized gains	4	19
Debt Securities, Gross unrealized losses	(49)	(9)
Debt securities, Estimated fair value	1,096	1,081
Foreign corporate debt securities
Schedule Of Available For Sale Securities [Line Items]
Debt Securities, Amortized cost	501	493
Debt Securities, Gross unrealized gains	2	9
Debt Securities, Gross unrealized losses	(22)	(4)
Debt securities, Estimated fair value	$ 481	$ 498

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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