Fair Value Measurements - Investments in Certain Other Invested Assets (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2025	Dec. 31, 2024
INVESTMENTS IN CERTAIN ENTITIES CARRIED AT FAIR VALUE USING NET ASSET VALUE PER SHARE
Fair Value Using NAV Per Share (or its equivalent)	$ 4,151	$ 4,032
Private Equity Funds and Hedge Funds
INVESTMENTS IN CERTAIN ENTITIES CARRIED AT FAIR VALUE USING NET ASSET VALUE PER SHARE
Fair Value Using NAV Per Share (or its equivalent)	3,459	3,292
Unfunded Commitments	1,111	792
Private equity funds
INVESTMENTS IN CERTAIN ENTITIES CARRIED AT FAIR VALUE USING NET ASSET VALUE PER SHARE
Fair Value Using NAV Per Share (or its equivalent)	3,269	3,105
Unfunded Commitments	$ 1,111	792
Average original expected lives (in years)	10 years
Private equity funds | Minimum
INVESTMENTS IN CERTAIN ENTITIES CARRIED AT FAIR VALUE USING NET ASSET VALUE PER SHARE
Extension period (in years)	1 year
Private equity funds | Maximum
INVESTMENTS IN CERTAIN ENTITIES CARRIED AT FAIR VALUE USING NET ASSET VALUE PER SHARE
Extension period (in years)	2 years
Leveraged buyout
INVESTMENTS IN CERTAIN ENTITIES CARRIED AT FAIR VALUE USING NET ASSET VALUE PER SHARE
Fair Value Using NAV Per Share (or its equivalent)	$ 1,141	1,126
Unfunded Commitments	336	375
Real assets
INVESTMENTS IN CERTAIN ENTITIES CARRIED AT FAIR VALUE USING NET ASSET VALUE PER SHARE
Fair Value Using NAV Per Share (or its equivalent)	817	782
Unfunded Commitments	222	261
Venture capital
INVESTMENTS IN CERTAIN ENTITIES CARRIED AT FAIR VALUE USING NET ASSET VALUE PER SHARE
Fair Value Using NAV Per Share (or its equivalent)	85	83
Unfunded Commitments	36	40
Growth equity
INVESTMENTS IN CERTAIN ENTITIES CARRIED AT FAIR VALUE USING NET ASSET VALUE PER SHARE
Fair Value Using NAV Per Share (or its equivalent)	181	175
Unfunded Commitments	3	1
Mezzanine
INVESTMENTS IN CERTAIN ENTITIES CARRIED AT FAIR VALUE USING NET ASSET VALUE PER SHARE
Fair Value Using NAV Per Share (or its equivalent)	105	120
Unfunded Commitments	55	58
Other
INVESTMENTS IN CERTAIN ENTITIES CARRIED AT FAIR VALUE USING NET ASSET VALUE PER SHARE
Fair Value Using NAV Per Share (or its equivalent)	940	819
Unfunded Commitments	459	57
Hedge funds
INVESTMENTS IN CERTAIN ENTITIES CARRIED AT FAIR VALUE USING NET ASSET VALUE PER SHARE
Fair Value Using NAV Per Share (or its equivalent)	190	187
Unfunded Commitments	0	0
Event-driven
INVESTMENTS IN CERTAIN ENTITIES CARRIED AT FAIR VALUE USING NET ASSET VALUE PER SHARE
Fair Value Using NAV Per Share (or its equivalent)	13	11
Unfunded Commitments	0	0
Long-short
INVESTMENTS IN CERTAIN ENTITIES CARRIED AT FAIR VALUE USING NET ASSET VALUE PER SHARE
Fair Value Using NAV Per Share (or its equivalent)	168	168
Unfunded Commitments	0	0
Other
INVESTMENTS IN CERTAIN ENTITIES CARRIED AT FAIR VALUE USING NET ASSET VALUE PER SHARE
Fair Value Using NAV Per Share (or its equivalent)	9	8
Unfunded Commitments	$ 0	$ 0