Debt Securities (Gross Unrealized Losses on Investments in Debt Securities) (Detail) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value, Less than 12 months	$ 5,739	$ 429
Unrealized losses, Less than 12 months	(80)	(3)
Estimated fair value, 12 months or longer	33	100
Unrealized losses, 12 months or longer	(2)	(1)
Estimated fair value, Total	5,772	529
Unrealized losses, Total	(82)	(4)
U.S. Treasury bonds
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value, Less than 12 months	76
Unrealized losses, Less than 12 months	(1)
Estimated fair value, 12 months or longer	0
Unrealized losses, 12 months or longer	0
Estimated fair value, Total	76
Unrealized losses, Total	(1)
Municipal bonds
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value, Less than 12 months	684	74
Unrealized losses, Less than 12 months	(17)	(1)
Estimated fair value, 12 months or longer	0	0
Unrealized losses, 12 months or longer	0	0
Estimated fair value, Total	684	74
Unrealized losses, Total	(17)	(1)
Foreign government bonds
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value, Less than 12 months	103	67
Unrealized losses, Less than 12 months	(1)	(1)
Estimated fair value, 12 months or longer	33	0
Unrealized losses, 12 months or longer	(2)	0
Estimated fair value, Total	136	67
Unrealized losses, Total	(3)	(1)
Governmental agency bonds
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value, Less than 12 months	73
Unrealized losses, Less than 12 months	(1)
Estimated fair value, 12 months or longer	0
Unrealized losses, 12 months or longer	0
Estimated fair value, Total	73
Unrealized losses, Total	(1)
Governmental agency mortgage-backed securities
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value, Less than 12 months	4,036	288
Unrealized losses, Less than 12 months	(47)	(1)
Estimated fair value, 12 months or longer	0	100
Unrealized losses, 12 months or longer	0	(1)
Estimated fair value, Total	4,036	388
Unrealized losses, Total	(47)	$ (2)
U.S. corporate debt securities
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value, Less than 12 months	533
Unrealized losses, Less than 12 months	(9)
Estimated fair value, 12 months or longer	0
Unrealized losses, 12 months or longer	0
Estimated fair value, Total	533
Unrealized losses, Total	(9)
Foreign corporate debt securities
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value, Less than 12 months	234
Unrealized losses, Less than 12 months	(4)
Estimated fair value, 12 months or longer	0
Unrealized losses, 12 months or longer	0
Estimated fair value, Total	234
Unrealized losses, Total	$ (4)

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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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), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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