Investment Information - Summary of available for sale securities (Details) - USD ($) $ in Millions	Sep. 30, 2023	Jun. 30, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	$ 24,167		$ 21,015
Gross Unrealized Gains	77		90
Gross Unrealized Losses	(1,415)		(1,649)
Allowance for Expected Credit Losses	(57)		(41)
Cost or Amortized Cost	25,562		22,615
Fixed maturities
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	22,485		19,683
Gross Unrealized Gains	74		89
Gross Unrealized Losses	(1,414)		(1,647)
Allowance for Expected Credit Losses	(57)	$ (61)	(41)	$ (46)	$ (59)	$ (3)
Cost or Amortized Cost	23,882		21,282
Fixed maturities | Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	10,064		8,020
Gross Unrealized Gains	33		55
Gross Unrealized Losses	(747)		(781)
Allowance for Expected Credit Losses	(47)	(50)	(30)	(37)	(40)	(2)
Cost or Amortized Cost	10,825		8,776
Fixed maturities | U.S. government and government agencies
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	5,662		5,162
Gross Unrealized Gains	15		15
Gross Unrealized Losses	(240)		(343)
Allowance for Expected Credit Losses	0		0
Cost or Amortized Cost	5,887		5,490
Fixed maturities | Asset backed securities
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	2,342		1,927
Gross Unrealized Gains	10		1
Gross Unrealized Losses	(76)		(107)
Allowance for Expected Credit Losses	(5)		(6)
Cost or Amortized Cost	2,413		2,039
Fixed maturities | Non-U.S. government securities
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	2,052		2,313
Gross Unrealized Gains	9		9
Gross Unrealized Losses	(173)		(238)
Allowance for Expected Credit Losses	(2)	$ (3)	(2)	$ 0	$ 0	$ 0
Cost or Amortized Cost	2,218		2,544
Fixed maturities | Commercial mortgage backed securities
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	1,102		1,047
Gross Unrealized Gains	0		1
Gross Unrealized Losses	(46)		(58)
Allowance for Expected Credit Losses	(3)		(3)
Cost or Amortized Cost	1,151		1,107
Fixed maturities | Residential mortgage backed securities
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	965		795
Gross Unrealized Gains	5		5
Gross Unrealized Losses	(100)		(87)
Allowance for Expected Credit Losses	0		0
Cost or Amortized Cost	1,060		877
Fixed maturities | Municipal bonds
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	298		419
Gross Unrealized Gains	2		3
Gross Unrealized Losses	(32)		(33)
Allowance for Expected Credit Losses	0		0
Cost or Amortized Cost	328		449
Short-term investments
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	1,682		1,332
Gross Unrealized Gains	3		1
Gross Unrealized Losses	(1)		(2)
Allowance for Expected Credit Losses	0		0
Cost or Amortized Cost	$ 1,680		$ 1,333