Investment Information - Summary of available for sale securities (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Fixed maturities:
Estimated fair value	$ 29,819	$ 25,616
Gross Unrealized Gains	181	276
Gross Unrealized Losses	(694)	(827)
Allowance for Expected Credit Losses	(22)	(28)
Cost or Amortized Cost	30,354	26,195
Fixed maturities available for sale, at fair value
Fixed maturities:
Estimated fair value	27,035	23,553
Gross Unrealized Gains	179	275
Gross Unrealized Losses	(692)	(825)
Allowance for Expected Credit Losses	(22)	(28)	$ (41)
Cost or Amortized Cost	27,570	24,131
Corporate bonds
Fixed maturities:
Estimated fair value	12,487	10,855
Gross Unrealized Gains	110	157
Gross Unrealized Losses	(346)	(464)
Allowance for Expected Credit Losses	(12)	(20)
Cost or Amortized Cost	12,735	11,182
US government and government agencies
Fixed maturities:
Estimated fair value	6,710	5,814
Gross Unrealized Gains	8	63
Gross Unrealized Losses	(149)	(86)
Allowance for Expected Credit Losses	0	0
Cost or Amortized Cost	6,851	5,837
Asset backed securities
Fixed maturities:
Estimated fair value	2,900	2,250
Gross Unrealized Gains	19	11
Gross Unrealized Losses	(32)	(55)
Allowance for Expected Credit Losses	(8)	(5)
Cost or Amortized Cost	2,921	2,299
Non-US government securities
Fixed maturities:
Estimated fair value	2,538	2,062
Gross Unrealized Gains	30	33
Gross Unrealized Losses	(107)	(100)
Allowance for Expected Credit Losses	(1)	(1)	$ (2)
Cost or Amortized Cost	2,616	2,130
Commercial mortgage backed securities
Fixed maturities:
Estimated fair value	1,058	1,213
Gross Unrealized Gains	6	3
Gross Unrealized Losses	(11)	(34)
Allowance for Expected Credit Losses	(1)	(2)
Cost or Amortized Cost	1,064	1,246
Mortgage backed securities
Fixed maturities:
Estimated fair value	1,079	1,103
Gross Unrealized Gains	6	7
Gross Unrealized Losses	(31)	(66)
Allowance for Expected Credit Losses	0	0
Cost or Amortized Cost	1,104	1,162
Municipal bonds
Fixed maturities:
Estimated fair value	263	256
Gross Unrealized Gains	0	1
Gross Unrealized Losses	(16)	(20)
Allowance for Expected Credit Losses	0	0
Cost or Amortized Cost	279	275
Short-term investments
Fixed maturities:
Estimated fair value	2,784	2,063
Gross Unrealized Gains	2	1
Gross Unrealized Losses	(2)	(2)
Allowance for Expected Credit Losses	0	0
Cost or Amortized Cost	$ 2,784	$ 2,064