Fair Value Measurements - Fair Value by Hierarchy (Details) - USD ($) $ in Millions	Sep. 30, 2022	Dec. 31, 2021
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	$ 35,717	$ 42,847
Fixed maturities, at fair value using the fair value option ("FVO")	335	160
Equity securities, at fair value	1,678	2,094
Derivative assets	12	7
Short-term investments	2,724	3,697
Total assets accounted for at fair value on a recurring basis	40,466	48,805
Liabilities accounted for at fair value on a recurring basis
Derivative liabilities	74	(49)
Total liabilities accounted for at fair value on a recurring basis	74	(49)
Credit derivatives
Assets accounted for at fair value on a recurring basis
Derivative assets	2	2
Liabilities accounted for at fair value on a recurring basis
Derivative liabilities	(2)	(4)
Foreign exchange derivatives
Assets accounted for at fair value on a recurring basis
Derivative assets	8	6
Liabilities accounted for at fair value on a recurring basis
Derivative liabilities	85	0
Interest rate derivatives
Assets accounted for at fair value on a recurring basis
Derivative assets	2	(1)
Liabilities accounted for at fair value on a recurring basis
Derivative liabilities	(9)	(45)
Asset backed securities ("ABS")
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	1,892	1,135
Collateralized Loan Obligations [Member]
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	2,919	3,025
CMBS
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	3,278	4,119
Corporate
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	14,888	18,707
Foreign government/government agencies
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	584	910
Municipal
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	6,197	8,257
RMBS
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	3,724	3,643
U.S. Treasuries
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	2,235	3,051
Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	46	882
Fixed maturities, at fair value using the fair value option ("FVO")	0	0
Equity securities, at fair value	1,154	1,453
Derivative assets	0	0
Short-term investments	927	1,627
Total assets accounted for at fair value on a recurring basis	2,127	3,962
Liabilities accounted for at fair value on a recurring basis
Derivative liabilities	0	0
Total liabilities accounted for at fair value on a recurring basis	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Credit derivatives
Assets accounted for at fair value on a recurring basis
Derivative assets	0	0
Liabilities accounted for at fair value on a recurring basis
Derivative liabilities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Foreign exchange derivatives
Assets accounted for at fair value on a recurring basis
Derivative assets	0	0
Liabilities accounted for at fair value on a recurring basis
Derivative liabilities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Interest rate derivatives
Assets accounted for at fair value on a recurring basis
Derivative assets	0	0
Liabilities accounted for at fair value on a recurring basis
Derivative liabilities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Asset backed securities ("ABS")
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Collateralized Loan Obligations [Member]
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | CMBS
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Foreign government/government agencies
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Municipal
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | RMBS
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Treasuries
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	46	882
Significant Observable Inputs (Level 2)
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	33,582	39,561
Fixed maturities, at fair value using the fair value option ("FVO")	149	0
Equity securities, at fair value	463	577
Derivative assets	12	6
Short-term investments	1,704	1,990
Total assets accounted for at fair value on a recurring basis	35,910	42,134
Liabilities accounted for at fair value on a recurring basis
Derivative liabilities	74	(48)
Total liabilities accounted for at fair value on a recurring basis	74	(48)
Significant Observable Inputs (Level 2) | Credit derivatives
Assets accounted for at fair value on a recurring basis
Derivative assets	2	2
Liabilities accounted for at fair value on a recurring basis
Derivative liabilities	(2)	(4)
Significant Observable Inputs (Level 2) | Foreign exchange derivatives
Assets accounted for at fair value on a recurring basis
Derivative assets	8	5
Liabilities accounted for at fair value on a recurring basis
Derivative liabilities	85	1
Significant Observable Inputs (Level 2) | Interest rate derivatives
Assets accounted for at fair value on a recurring basis
Derivative assets	2	(1)
Liabilities accounted for at fair value on a recurring basis
Derivative liabilities	(9)	(45)
Significant Observable Inputs (Level 2) | Asset backed securities ("ABS")
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	1,892	1,135
Significant Observable Inputs (Level 2) | Collateralized Loan Obligations [Member]
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	2,764	2,768
Significant Observable Inputs (Level 2) | CMBS
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	3,058	3,923
Significant Observable Inputs (Level 2) | Corporate
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	13,286	17,089
Significant Observable Inputs (Level 2) | Foreign government/government agencies
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	580	905
Significant Observable Inputs (Level 2) | Municipal
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	6,197	8,257
Significant Observable Inputs (Level 2) | RMBS
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	3,616	3,315
Significant Observable Inputs (Level 2) | U.S. Treasuries
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	2,189	2,169
Significant Unobservable Inputs (Level 3)
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	2,089	2,404
Fixed maturities, at fair value using the fair value option ("FVO")	186	160
Equity securities, at fair value	61	64
Derivative assets	0	1
Short-term investments	93	80
Total assets accounted for at fair value on a recurring basis	2,429	2,709
Liabilities accounted for at fair value on a recurring basis
Derivative liabilities	0	(1)
Total liabilities accounted for at fair value on a recurring basis	0	(1)
Significant Unobservable Inputs (Level 3) | Credit derivatives
Assets accounted for at fair value on a recurring basis
Derivative assets	0	0
Liabilities accounted for at fair value on a recurring basis
Derivative liabilities	0	0
Significant Unobservable Inputs (Level 3) | Foreign exchange derivatives
Assets accounted for at fair value on a recurring basis
Derivative assets	0	1
Liabilities accounted for at fair value on a recurring basis
Derivative liabilities	0	(1)
Significant Unobservable Inputs (Level 3) | Interest rate derivatives
Assets accounted for at fair value on a recurring basis
Derivative assets	0	0
Liabilities accounted for at fair value on a recurring basis
Derivative liabilities	0	0
Significant Unobservable Inputs (Level 3) | Asset backed securities ("ABS")
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	0	0
Significant Unobservable Inputs (Level 3) | Collateralized Loan Obligations [Member]
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	155	257
Significant Unobservable Inputs (Level 3) | CMBS
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	220	196
Significant Unobservable Inputs (Level 3) | Corporate
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	1,602	1,618
Significant Unobservable Inputs (Level 3) | Foreign government/government agencies
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	4	5
Significant Unobservable Inputs (Level 3) | Municipal
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	0	0
Significant Unobservable Inputs (Level 3) | RMBS
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	108	328
Significant Unobservable Inputs (Level 3) | U.S. Treasuries
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	$ 0	$ 0