Investment Information - Summary of available for sale securities (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Available for sale securities:
Estimated fair value	$ 25,616	$ 21,015
Gross Unrealized Gains	276	90
Gross Unrealized Losses	(827)	(1,649)
Allowance for Expected Credit Losses	(28)	(41)
Cost or Amortized Cost	26,195	22,615
Fixed maturities available for sale, at fair value
Available for sale securities:
Estimated fair value	23,553	19,683
Gross Unrealized Gains	275	89
Gross Unrealized Losses	(825)	(1,647)
Allowance for Expected Credit Losses	(28)	(41)	$ (3)
Cost or Amortized Cost	24,131	21,282
Corporate bonds
Available for sale securities:
Estimated fair value	10,855	8,020
Gross Unrealized Gains	157	55
Gross Unrealized Losses	(464)	(781)
Allowance for Expected Credit Losses	(20)	(30)
Cost or Amortized Cost	11,182	8,776
US government and government agencies
Available for sale securities:
Estimated fair value	5,814	5,162
Gross Unrealized Gains	63	15
Gross Unrealized Losses	(86)	(343)
Allowance for Expected Credit Losses	0	0
Cost or Amortized Cost	5,837	5,490
Asset backed securities
Available for sale securities:
Estimated fair value	2,250	1,927
Gross Unrealized Gains	11	1
Gross Unrealized Losses	(55)	(107)
Allowance for Expected Credit Losses	(5)	(6)
Cost or Amortized Cost	2,299	2,039
Non-US government securities
Available for sale securities:
Estimated fair value	2,062	2,313
Gross Unrealized Gains	33	9
Gross Unrealized Losses	(100)	(238)
Allowance for Expected Credit Losses	(1)	(2)	$ 0
Cost or Amortized Cost	2,130	2,544
Commercial mortgage backed securities
Available for sale securities:
Estimated fair value	1,213	1,047
Gross Unrealized Gains	3	1
Gross Unrealized Losses	(34)	(58)
Allowance for Expected Credit Losses	(2)	(3)
Cost or Amortized Cost	1,246	1,107
Mortgage backed securities
Available for sale securities:
Estimated fair value	1,103	795
Gross Unrealized Gains	7	5
Gross Unrealized Losses	(66)	(87)
Allowance for Expected Credit Losses	0	0
Cost or Amortized Cost	1,162	877
Municipal bonds
Available for sale securities:
Estimated fair value	256	419
Gross Unrealized Gains	1	3
Gross Unrealized Losses	(20)	(33)
Allowance for Expected Credit Losses	0	0
Cost or Amortized Cost	275	449
Short-term investments
Available for sale securities:
Estimated fair value	2,063	1,332
Gross Unrealized Gains	1	1
Gross Unrealized Losses	(2)	(2)
Allowance for Expected Credit Losses	0	0
Cost or Amortized Cost	$ 2,064	$ 1,333

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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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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