Investments - Summary of Amortized Cost and Estimated Fair Value of Available-for-Sale Investments, Excluding VIE Investments (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 794	$ 810
Debt Securities, Available-for-sale, Amortized Cost	2,006	2,140
Debt Securities, Available-for-sale, Allowance for Credit Loss	1	0	$ 0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	73	141
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	598	768
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	26	14
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	196	41
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	17	1
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	43	16
Available-for-sale Securities, Current	2,036	2,265
Fixed maturity securities, at fair value	2,036
Short-term Investments [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	30	128
Debt Securities, Available-for-sale, Amortized Cost	540	415
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	18	114
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	12	13
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0	0
Fixed maturity securities, at fair value	540	414
Fixed Income Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	764	682
Debt Securities, Available-for-sale, Amortized Cost	1,352	1,605
Debt Securities, Available-for-sale, Allowance for Credit Loss	1	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	73	141
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	580	654
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	26	14
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	184	28
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	16	1
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	42	16
Fixed maturity securities, at fair value	1,383	1,730
Fixed Income Securities [Member] \| Municipal Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	19	118
Debt Securities, Available-for-sale, Amortized Cost	65	315
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	5	28
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	19	117
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1	3
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	1	2
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	1	3
Fixed maturity securities, at fair value	69	340
Fixed Income Securities [Member] \| Corporate Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	466	380
Debt Securities, Available-for-sale, Amortized Cost	610	612
Debt Securities, Available-for-sale, Allowance for Credit Loss	1	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	2	10
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	349	363
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	21	8
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	117	17
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	13	1
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	34	9
Fixed maturity securities, at fair value	577	613
Fixed Income Securities [Member] \| Foreign Obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	87	78
Debt Securities, Available-for-sale, Amortized Cost	92	89
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	36	75
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1	2
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	51	3
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	3	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	4	2
Fixed maturity securities, at fair value	88	87
Fixed Income Securities [Member] \| US Government Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	49	27
Debt Securities, Available-for-sale, Amortized Cost	53	45
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0	1
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	44	25
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	5	2
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	2	1
Fixed maturity securities, at fair value	51	45
Fixed Income Securities [Member] \| Residential Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	17	2
Debt Securities, Available-for-sale, Amortized Cost	179	182
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	47	70
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	16	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	1	1
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0	0
Fixed maturity securities, at fair value	225	252
Fixed Income Securities [Member] \| Collateralized Debt Obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	120	71
Debt Securities, Available-for-sale, Amortized Cost	121	128
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	111	68
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	9	3
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	1	0
Fixed maturity securities, at fair value	120	128
Fixed Income Securities [Member] \| Asset-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	6	6
Debt Securities, Available-for-sale, Amortized Cost	232	234
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	20	32
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	6	6
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0	0
Fixed maturity securities, at fair value	252	265
Fixed Income Investments And Other Investments [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	1,892	2,020
Debt Securities, Available-for-sale, Allowance for Credit Loss	1	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	73	141
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	42	16
Fixed maturity securities, at fair value	1,922	2,145
Collateral Pledged [Member] \| Fixed Income Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0	0
Fixed maturity securities, at fair value	114	120
Collateral Pledged [Member] \| Fixed Income Securities [Member] \| Short-term Investments [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	99	105
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0	0
Fixed maturity securities, at fair value	99	105
Collateral Pledged [Member] \| Fixed Income Securities [Member] \| US Treasury and Government
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	15	15
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0	0
Fixed maturity securities, at fair value	15	15
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]
Debt Securities, Available-for-sale, Amortized Cost	114	120
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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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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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 accumulated unrealized loss on 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 12 months or longer, 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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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position without allowance for credit loss.

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