Investments - Summary of Amortized Cost and Estimated Fair Value of Available-for-Sale Investments, Excluding VIE Investments (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2023	Sep. 30, 2023	Dec. 31, 2022	Sep. 30, 2022
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Allowance for Credit Loss	$ 2	$ 2	$ 0	$ 0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	27	27	31
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	20	20	53
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	849	849	400
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	102	102	53
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	122	122	106
Fixed maturity securities, at fair value	2,004	2,004
Debt Securities, Available-for-Sale, Allowance for Credit Loss, Period Increase (Decrease)	1	2
Short-term Investments [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	19	19	86
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	19	19	78
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	0	0	8
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0	0	0
Fixed maturity securities, at fair value	421	421	507
Fixed Income Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	1,306	1,306	1,183
Debt Securities, Available-for-sale, Allowance for Credit Loss	2	2	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	27	27	31
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	456	456	791
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	20	20	53
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	849	849	392
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	102	102	53
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	122	122	106
Fixed maturity securities, at fair value	1,556	1,556	1,395
Fixed Income Securities [Member] \| Municipal Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	65	65	28
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	50	50	21
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1	1	1
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	16	16	7
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	2	2	1
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	3	3	2
Fixed maturity securities, at fair value	67	67	43
Fixed Income Securities [Member] \| Corporate Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	648	648	559
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0	0	1
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	150	150	280
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	5	5	21
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	497	497	279
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	60	60	42
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	65	65	63
Fixed maturity securities, at fair value	671	671	598
Fixed Income Securities [Member] \| Foreign Obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	77	77	73
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	25	25	27
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1	1	2
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	52	52	47
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	9	9	7
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	9	9	9
Fixed maturity securities, at fair value	92	92	76
Fixed Income Securities [Member] \| US Government Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	64	64	58
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	28	28	40
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	2	2	3
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	37	37	19
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	3	3	1
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	4	4	4
Fixed maturity securities, at fair value	73	73	65
Fixed Income Securities [Member] \| Residential Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	165	165	132
Debt Securities, Available-for-sale, Allowance for Credit Loss	2	2	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	23	23	28
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	58	58	132
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	2	2	19
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	107	107	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	25	25	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	28	28	19
Fixed maturity securities, at fair value	227	227	238
Fixed Income Securities [Member] \| Collateralized Debt Obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	114	114	126
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	7	7	90
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	0	3
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	107	107	36
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	1	1	1
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	1	1	4
Fixed maturity securities, at fair value	142	142	137
Fixed Income Securities [Member] \| Asset-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	154	154	203
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	3	3	2
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	120	120	198
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	9	9	4
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	34	34	5
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	2	2	1
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	11	11	5
Fixed maturity securities, at fair value	265	265	224
Fixed Income Securities [Member] \| Commercial Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	18	18	3
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	18	18	3
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1	1	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	0	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	1	1	0
Fixed maturity securities, at fair value	18	18
Fixed Income Securities [Member] \| Collateralized Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	1	1	0
Fixed maturity securities, at fair value	18	18	15
Fixed Income Investments And Other Investments [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Allowance for Credit Loss	2	2	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	27	27	31
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	122	122	106
Fixed maturity securities, at fair value	1,977	1,977	1,902
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	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0	0	0
Fixed maturity securities, at fair value	27	27	64
Collateral Pledged [Member] \| Fixed Income Securities [Member] \| Short-term Investments [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0	0	0
Fixed maturity securities, at fair value	27	27	64
Asset Pledged as Collateral [Member] \| Fixed Income Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Allowance for Credit Loss	$ 0	$ 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 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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