Investments - Summary of Amortized Cost and Estimated Fair Value of Available-for-Sale Investments, Excluding VIE Investments (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 1,145	$ 1,032
Debt Securities, Available-for-sale, Allowance for Credit Loss	2	3	$ 1
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	37	40
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	305	187
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	4	4
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	839	844
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	70	68
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	75	71
Fixed maturity securities, at fair value	2,095
Debt Securities, Available-for-sale, Amortized Cost	2,135	2,197
Debt Securities, Available-for-Sale, Allowance for Credit Loss, Period Increase (Decrease)	0
Short-term Investments [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	44	4
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	44	4
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	382	426
Debt Securities, Available-for-sale, Amortized Cost	382	426
Fixed Income Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	1,101	1,028
Debt Securities, Available-for-sale, Allowance for Credit Loss	2	3
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	37	40
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	261	184
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	4	4
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	839	844
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	70	68
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	74	71
Fixed maturity securities, at fair value	1,687	1,710
Debt Securities, Available-for-sale, Amortized Cost	1,726	1,744
Fixed Income Securities [Member] \| Municipal Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	29	23
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	1	1
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	13	7
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	16	16
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	1	1
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	1	1
Fixed maturity securities, at fair value	72	72
Debt Securities, Available-for-sale, Amortized Cost	72	72
Fixed Income Securities [Member] \| Corporate Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	596	584
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	3	4
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	91	75
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	2	2
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	504	509
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	44	43
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	45	44
Fixed maturity securities, at fair value	765	745
Debt Securities, Available-for-sale, Amortized Cost	807	785
Fixed Income Securities [Member] \| Foreign Obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	66	64
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	1	1
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	9	8
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	57	56
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	7	6
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	7	6
Fixed maturity securities, at fair value	99	100
Debt Securities, Available-for-sale, Amortized Cost	105	105
Fixed Income Securities [Member] \| US Government Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	73	63
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	40	27
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1	1
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	33	37
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	2	2
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	4	4
Fixed maturity securities, at fair value	98	82
Debt Securities, Available-for-sale, Amortized Cost	101	85
Fixed Income Securities [Member] \| Residential Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	153	104
Debt Securities, Available-for-sale, Allowance for Credit Loss	2	3
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	28	28
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	42	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	111	98
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	12	14
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	12	14
Fixed maturity securities, at fair value	253	250
Debt Securities, Available-for-sale, Amortized Cost	239	239
Fixed Income Securities [Member] \| Collateralized Debt Obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	53	95
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	1	1
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	13	1
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	40	93
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	1
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0	1
Fixed maturity securities, at fair value	143	139
Debt Securities, Available-for-sale, Amortized Cost	143	139
Fixed Income Securities [Member] \| Asset-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	132	92
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	3	3
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	53	57
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1	1
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	79	35
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	4	1
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	5	1
Fixed maturity securities, at fair value	231	303
Debt Securities, Available-for-sale, Amortized Cost	232	301
Fixed Income Securities [Member] \| Commercial Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	0	3
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	0	3
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	27
Debt Securities, Available-for-sale, Amortized Cost	27
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
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	27	19
Debt Securities, Available-for-sale, Amortized Cost	27	19
Fixed Income Investments And Other Investments [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Allowance for Credit Loss	2	3
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	37	40
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	74	71
Fixed maturity securities, at fair value	2,068	2,135
Debt Securities, Available-for-sale, Amortized Cost	2,108	2,170
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	1	0
Fixed maturity securities, at fair value	26	27
Debt Securities, Available-for-sale, Amortized Cost	27	0
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
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	0	27
Debt Securities, Available-for-sale, Amortized Cost	0	27
Collateral Pledged [Member] \| Fixed Income Securities [Member] \| US Treasury and Government
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Allowance for Credit Loss	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	1	0
Fixed maturity securities, at fair value	26	0
Debt Securities, Available-for-sale, Amortized Cost	27	0
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
Debt Securities, Available-for-sale, Amortized Cost	$ 27	$ 27

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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