Investments - Summary of Amortized Cost and Estimated Fair Value of Available-for-Sale Investments, Excluding VIE Investments (Detail) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 2,140
Gross Unrealized Gains	141	$ 149
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	16	8
Available-for-sale Securities, Current	2,265	2,949
Estimated Fair Value	2,265
Available-for-sale Securities, Amortized Cost Basis	2,140	2,807
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	16	8
Short-term Investments [Member]
Debt Securities, Available-for-sale [Line Items]
Gross Unrealized Gains	0	0
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0	0
Estimated Fair Value	414	492
Available-for-sale Securities, Amortized Cost Basis	415	492
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0	0
Fixed Income Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,605	2,175
Gross Unrealized Gains	141	149
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	16	8
Estimated Fair Value	1,730	2,317
Available-for-sale Securities, Amortized Cost Basis	1,605	2,175
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	16	8
Fixed Income Securities [Member] \| Municipal Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Gross Unrealized Gains	28	37
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	3	0
Estimated Fair Value	340	358
Available-for-sale Securities, Amortized Cost Basis	315	321
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	3	0
Fixed Income Securities [Member] \| Corporate Obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Gross Unrealized Gains	10	24
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	9	6
Estimated Fair Value	613	1,077
Available-for-sale Securities, Amortized Cost Basis	612	1,059
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	9	6
Fixed Income Securities [Member] \| Debt Security, Government, Non-US [Member]
Debt Securities, Available-for-sale [Line Items]
Gross Unrealized Gains	0	1
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	2	0
Estimated Fair Value	87	98
Available-for-sale Securities, Amortized Cost Basis	89	97
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	2	0
Fixed Income Securities [Member] \| U.S. Government Obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Gross Unrealized Gains	1	2
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	1	1
Estimated Fair Value	45	106
Available-for-sale Securities, Amortized Cost Basis	45	105
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	1	1
Fixed Income Securities [Member] \| Residential Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	182
Gross Unrealized Gains	70	46
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0	0
Estimated Fair Value	252	302
Available-for-sale Securities, Amortized Cost Basis	182	256
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0	0
Fixed Income Securities [Member] \| Collateralized Debt Obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	128
Gross Unrealized Gains	0	0
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0	0
Estimated Fair Value	128	74
Available-for-sale Securities, Amortized Cost Basis	128	74
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0	0
Fixed Income Securities [Member] \| Asset-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	234
Gross Unrealized Gains	32	40
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0	0
Estimated Fair Value	265	303
Available-for-sale Securities, Amortized Cost Basis	234	263
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0	0
Fixed Income Investments And Other Investments [Member]
Debt Securities, Available-for-sale [Line Items]
Gross Unrealized Gains	141	149
Estimated Fair Value	2,145	2,809
Available-for-sale Securities, Amortized Cost Basis	2,020	2,667
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	16	8
Collateral Pledged [Member]
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	120	140
Collateral Pledged [Member] \| Fixed Income Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	15	15
Gross Unrealized Gains	0	0
Estimated Fair Value	15	15
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0	0
Collateral Pledged [Member] \| Fixed Income Securities [Member] \| Short-term Investments [Member]
Debt Securities, Available-for-sale [Line Items]
Gross Unrealized Gains	0	0
Estimated Fair Value	105	125
Available-for-sale Securities, Amortized Cost Basis	105	125
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0	0
Collateral Pledged [Member] \| Fixed Income Securities [Member] \| US Treasury and Government
Debt Securities, Available-for-sale [Line Items]
Gross Unrealized Gains	0	0
Estimated Fair Value	15	15
Available-for-sale Securities, Amortized Cost Basis	15	15
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0	0
Asset Pledged as Collateral [Member] \| Fixed Income Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Amortized Cost Basis	120	140
Debt Securities, Available-for-sale, Allowance for Credit Loss	$ 0	$ 0

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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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).

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount of investment in debt and equity securities categorized neither as trading securities nor held-to-maturity securities and intended be sold or mature one year or operating cycle, if longer.

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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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Amount of allowance for credit loss 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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