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Investments - Available for sale fixed maturities (Details) - USD ($) $ in Millions	Sep. 30, 2024	Jun. 30, 2024	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, available for sale, amortized cost	$ 10,586		$ 10,752
Fixed maturities, available for sale, allowance for expected credit losses	25	$ 10	12	$ 20	$ 16	$ 11
Available for sale (AFS) fixed maturities	10,435		10,377
Total fixed maturities
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, available for sale, amortized cost	10,586		10,752
Fixed maturities, available for sale, allowance for expected credit losses	25		12
Fixed maturities, available for sale, gross unrealized, gains	173		107
Fixed maturities, available for sale, gross unrealized, losses	(299)		(470)
Fixed maturities, available-for-sale securities, accumulated gross unrealized gain (loss), before tax	(126)		(363)
Available for sale (AFS) fixed maturities	10,435		10,377
U.S. government and government agencies
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, available for sale, amortized cost	182		243
Fixed maturities, available for sale, allowance for expected credit losses	0		0
Fixed maturities, available for sale, gross unrealized, gains	1		1
Fixed maturities, available for sale, gross unrealized, losses	(3)		(8)
Fixed maturities, available-for-sale securities, accumulated gross unrealized gain (loss), before tax	(2)		(7)
Available for sale (AFS) fixed maturities	180		236
States, municipalities and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, available for sale, amortized cost	895		1,014
Fixed maturities, available for sale, allowance for expected credit losses	0		0
Fixed maturities, available for sale, gross unrealized, gains	6		8
Fixed maturities, available for sale, gross unrealized, losses	(34)		(38)
Fixed maturities, available-for-sale securities, accumulated gross unrealized gain (loss), before tax	(28)		(30)
Available for sale (AFS) fixed maturities	867		984
Foreign government
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, available for sale, amortized cost	240		236
Fixed maturities, available for sale, allowance for expected credit losses	0		0
Fixed maturities, available for sale, gross unrealized, gains	3		1
Fixed maturities, available for sale, gross unrealized, losses	(2)		(7)
Fixed maturities, available-for-sale securities, accumulated gross unrealized gain (loss), before tax	1		(6)
Available for sale (AFS) fixed maturities	241		230
Residential MBS
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, available for sale, amortized cost	1,893		1,788
Fixed maturities, available for sale, allowance for expected credit losses	1		1
Fixed maturities, available for sale, gross unrealized, gains	36		26
Fixed maturities, available for sale, gross unrealized, losses	(117)		(155)
Fixed maturities, available-for-sale securities, accumulated gross unrealized gain (loss), before tax	(81)		(129)
Available for sale (AFS) fixed maturities	1,811		1,658
Commercial MBS
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, available for sale, amortized cost	51		75
Fixed maturities, available for sale, allowance for expected credit losses	0		0
Fixed maturities, available for sale, gross unrealized, gains	0		0
Fixed maturities, available for sale, gross unrealized, losses	0		(1)
Fixed maturities, available-for-sale securities, accumulated gross unrealized gain (loss), before tax	0		(1)
Available for sale (AFS) fixed maturities	51		74
Collateralized loan obligations
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, available for sale, amortized cost	1,301		1,709
Fixed maturities, available for sale, allowance for expected credit losses	3		3
Fixed maturities, available for sale, gross unrealized, gains	11		9
Fixed maturities, available for sale, gross unrealized, losses	(11)		(28)
Fixed maturities, available-for-sale securities, accumulated gross unrealized gain (loss), before tax	0		(19)
Available for sale (AFS) fixed maturities	1,298		1,687
Other asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, available for sale, amortized cost	2,465		2,477
Fixed maturities, available for sale, allowance for expected credit losses	6		5
Fixed maturities, available for sale, gross unrealized, gains	28		10
Fixed maturities, available for sale, gross unrealized, losses	(62)		(120)
Fixed maturities, available-for-sale securities, accumulated gross unrealized gain (loss), before tax	(34)		(110)
Available for sale (AFS) fixed maturities	2,425		2,362
Corporate and other
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, available for sale, amortized cost	3,559		3,210
Fixed maturities, available for sale, allowance for expected credit losses	15	$ 0	3	$ 8	$ 5	$ 1
Fixed maturities, available for sale, gross unrealized, gains	88		52
Fixed maturities, available for sale, gross unrealized, losses	(70)		(113)
Fixed maturities, available-for-sale securities, accumulated gross unrealized gain (loss), before tax	18		(61)
Available for sale (AFS) fixed maturities	$ 3,562		$ 3,146