Fair Value Measurements - Investments in Certain Other Invested Assets (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 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)	$ 3,889	$ 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)	3,502	3,292
Unfunded Commitments	1,147	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)	3,311	3,105
Unfunded Commitments	$ 1,147	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)	$ 1,166	1,126
Unfunded Commitments	326	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)	741	782
Unfunded Commitments	115	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)	88	83
Unfunded Commitments	34	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)	187	175
Unfunded Commitments	2	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)	92	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)	1,037	819
Unfunded Commitments	615	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)	191	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)	11	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)	171	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