Fair Value of Financial Instruments - Schedule of Fair Value Hierarchy Measurements of Financial Instruments (Details) - USD ($) $ in Millions	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022
Financial assets
Equity securities	$ 1,200		$ 1,404
Short-term investments	1,945		2,397
Derivative assets	1,610		227
Other assets - market risk benefit assets	704		34
Separate account assets	1,266		1,189
Financial liabilities
Market risk benefits	3,276		34
Separate account liabilities	1,266	$ 1,285	1,189	$ 1,145	$ 1,098	$ 1,045
Separate accounts not subject to fair value hierarchy	32		26
Total Fair Value
Financial assets
Fixed maturity securities, available for sale	46,480		12,877
Equity securities	1,200		1,404
Real estate at fair value	1,279		0
Real estate partnerships at fair value	39		0
Investment funds (fair value option)	111		0
Short-term investments	1,945		2,397
Derivative assets	1,610		227
Collaterals received on derivatives (excluding excess collateral)	(1,587)		(226)
Separately managed accounts	89		105
Other invested assets - other	425		0
Cash and cash equivalents	13,895		3,192
Other assets - market risk benefit assets	704		34
Separate account assets	1,234		1,163
Total financial assets	67,424		21,173
Financial liabilities
Policyholders’ account balances – embedded derivative	1,196		873
Market risk benefits	3,276		34
Funds withheld liabilities	79		0
Separate account liabilities	1,234		1,163
Total financial liabilities	5,785		2,070
Total Fair Value | U.S. treasury and government
Financial assets
Fixed maturity securities, available for sale	83		62
Total Fair Value | U.S. states and political subdivisions
Financial assets
Fixed maturity securities, available for sale	3,299		578
Total Fair Value | Foreign governments
Financial assets
Fixed maturity securities, available for sale	453		9
Total Fair Value | Corporate debt securities
Financial assets
Fixed maturity securities, available for sale	31,949		10,784
Total Fair Value | Residential mortgage-backed securities
Financial assets
Fixed maturity securities, available for sale	1,079		127
Total Fair Value | Commercial mortgage-backed securities
Financial assets
Fixed maturity securities, available for sale	2,766		0
Total Fair Value | Collateralized debt securities
Financial assets
Fixed maturity securities, available for sale	6,851		1,317
Total Fair Value | Common stock
Financial assets
Equity securities	1,081		1,307
Total Fair Value | Preferred stock
Financial assets
Equity securities	114		97
Total Fair Value | Private equity and other
Financial assets
Equity securities	5		0
Level 1
Financial assets
Fixed maturity securities, available for sale	83		62
Equity securities	407		336
Real estate at fair value	0		0
Real estate partnerships at fair value	0		0
Investment funds (fair value option)	0		0
Short-term investments	823		1,100
Derivative assets	0		0
Collaterals received on derivatives (excluding excess collateral)	(1,587)		0
Separately managed accounts	0		0
Other invested assets - other	0		0
Cash and cash equivalents	13,895		3,192
Other assets - market risk benefit assets	0		0
Separate account assets	200		406
Total financial assets	13,821		5,096
Financial liabilities
Policyholders’ account balances – embedded derivative	0		0
Market risk benefits	0		0
Funds withheld liabilities	0		0
Separate account liabilities	200		406
Total financial liabilities	200		406
Level 1 | U.S. treasury and government
Financial assets
Fixed maturity securities, available for sale	83		62
Level 1 | U.S. states and political subdivisions
Financial assets
Fixed maturity securities, available for sale	0		0
Level 1 | Foreign governments
Financial assets
Fixed maturity securities, available for sale	0		0
Level 1 | Corporate debt securities
Financial assets
Fixed maturity securities, available for sale	0		0
Level 1 | Residential mortgage-backed securities
Financial assets
Fixed maturity securities, available for sale	0		0
Level 1 | Commercial mortgage-backed securities
Financial assets
Fixed maturity securities, available for sale	0		0
Level 1 | Collateralized debt securities
Financial assets
Fixed maturity securities, available for sale	0		0
Level 1 | Common stock
Financial assets
Equity securities	384		314
Level 1 | Preferred stock
Financial assets
Equity securities	23		22
Level 1 | Private equity and other
Financial assets
Equity securities	0		0
Level 2
Financial assets
Fixed maturity securities, available for sale	40,110		9,700
Equity securities	2		0
Real estate at fair value	0		0
Real estate partnerships at fair value	0		0
Investment funds (fair value option)	0		0
Short-term investments	544		0
Derivative assets	1,356		0
Collaterals received on derivatives (excluding excess collateral)	0		0
Separately managed accounts	0		0
Other invested assets - other	0		0
Cash and cash equivalents	0		0
Other assets - market risk benefit assets	0		0
Separate account assets	1,034		757
Total financial assets	43,046		10,457
Financial liabilities
Policyholders’ account balances – embedded derivative	0		0
Market risk benefits	0		0
Funds withheld liabilities	0		0
Separate account liabilities	1,034		757
Total financial liabilities	1,034		757
Level 2 | U.S. treasury and government
Financial assets
Fixed maturity securities, available for sale	0		0
Level 2 | U.S. states and political subdivisions
Financial assets
Fixed maturity securities, available for sale	3,047		578
Level 2 | Foreign governments
Financial assets
Fixed maturity securities, available for sale	453		9
Level 2 | Corporate debt securities
Financial assets
Fixed maturity securities, available for sale	29,035		8,570
Level 2 | Residential mortgage-backed securities
Financial assets
Fixed maturity securities, available for sale	1,057		127
Level 2 | Commercial mortgage-backed securities
Financial assets
Fixed maturity securities, available for sale	2,743		0
Level 2 | Collateralized debt securities
Financial assets
Fixed maturity securities, available for sale	3,775		416
Level 2 | Common stock
Financial assets
Equity securities	2		0
Level 2 | Preferred stock
Financial assets
Equity securities	0		0
Level 2 | Private equity and other
Financial assets
Equity securities	0		0
Level 3
Financial assets
Fixed maturity securities, available for sale	6,287		3,115
Equity securities	791		1,068
Real estate at fair value	1,279		0
Real estate partnerships at fair value	39		0
Investment funds (fair value option)	111		0
Short-term investments	578		1,297
Derivative assets	254		227
Collaterals received on derivatives (excluding excess collateral)	0		(226)
Separately managed accounts	89		105
Other invested assets - other	425		0
Cash and cash equivalents	0		0
Other assets - market risk benefit assets	704		34
Separate account assets	0		0
Total financial assets	10,557		5,620
Financial liabilities
Policyholders’ account balances – embedded derivative	1,196		873
Market risk benefits	3,276		34
Funds withheld liabilities	79		0
Separate account liabilities	0		0
Total financial liabilities	4,551		907
Level 3 | U.S. treasury and government
Financial assets
Fixed maturity securities, available for sale	0		0
Level 3 | U.S. states and political subdivisions
Financial assets
Fixed maturity securities, available for sale	252		0
Level 3 | Foreign governments
Financial assets
Fixed maturity securities, available for sale	0		0
Level 3 | Corporate debt securities
Financial assets
Fixed maturity securities, available for sale	2,914		2,214
Level 3 | Residential mortgage-backed securities
Financial assets
Fixed maturity securities, available for sale	22		0
Level 3 | Commercial mortgage-backed securities
Financial assets
Fixed maturity securities, available for sale	23		0
Level 3 | Collateralized debt securities
Financial assets
Fixed maturity securities, available for sale	3,076		901
Level 3 | Common stock
Financial assets
Equity securities	695		993
Level 3 | Preferred stock
Financial assets
Equity securities	91		75
Level 3 | Private equity and other
Financial assets
Equity securities	5		$ 0
Fair Value Measured at Net Asset Value Per Share
Financial assets
Investment funds (fair value option)	$ 360