Fair Value Measurements - Fair Value by Hierarchy (Details) - USD ($) $ in Millions	Jun. 30, 2022	Dec. 31, 2021
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	$ 37,887	$ 42,847
Fixed maturities, at fair value using the fair value option ("FVO")	342	160
Equity securities, at fair value	1,728	2,094
Derivative assets	32	7
Short-term investments	2,524	3,697
Total assets accounted for at fair value on a recurring basis	42,513	48,805
Liabilities accounted for at fair value on a recurring basis
Derivative liabilities	2	49
Total liabilities accounted for at fair value on a recurring basis	2	49
Credit derivatives
Assets accounted for at fair value on a recurring basis
Derivative assets	3	2
Liabilities accounted for at fair value on a recurring basis
Derivative liabilities	3	4
Foreign exchange derivatives
Assets accounted for at fair value on a recurring basis
Derivative assets	29	6
Liabilities accounted for at fair value on a recurring basis
Derivative liabilities	(25)	0
Interest rate derivatives
Assets accounted for at fair value on a recurring basis
Derivative assets		(1)
Liabilities accounted for at fair value on a recurring basis
Derivative liabilities	20	45
Asset backed securities ("ABS")
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	1,342	1,135
Collateralized Loan Obligations [Member]
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	2,890	3,025
CMBS
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	3,398	4,119
Corporate
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	16,151	18,707
Foreign government/government agencies
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	661	910
Municipal
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	7,067	8,257
RMBS
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	3,929	3,643
U.S. Treasuries
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	2,449	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	0	882
Fixed maturities, at fair value using the fair value option ("FVO")	0	0
Equity securities, at fair value	1,203	1,453
Derivative assets	0	0
Short-term investments	754	1,627
Total assets accounted for at fair value on a recurring basis	1,957	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
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	0	882
Significant Observable Inputs (Level 2)
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	35,755	39,561
Fixed maturities, at fair value using the fair value option ("FVO")	149	0
Equity securities, at fair value	465	577
Derivative assets	32	6
Short-term investments	1,710	1,990
Total assets accounted for at fair value on a recurring basis	38,111	42,134
Liabilities accounted for at fair value on a recurring basis
Derivative liabilities	(2)	48
Total liabilities accounted for at fair value on a recurring basis	(2)	48
Significant Observable Inputs (Level 2) | Credit derivatives
Assets accounted for at fair value on a recurring basis
Derivative assets	3	2
Liabilities accounted for at fair value on a recurring basis
Derivative liabilities	3	4
Significant Observable Inputs (Level 2) | Foreign exchange derivatives
Assets accounted for at fair value on a recurring basis
Derivative assets	29	5
Liabilities accounted for at fair value on a recurring basis
Derivative liabilities	(25)	(1)
Significant Observable Inputs (Level 2) | Interest rate derivatives
Assets accounted for at fair value on a recurring basis
Derivative assets		(1)
Liabilities accounted for at fair value on a recurring basis
Derivative liabilities	20	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	1,342	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	2,726	2,768
Significant Observable Inputs (Level 2) | CMBS
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	3,174	3,923
Significant Observable Inputs (Level 2) | Corporate
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	14,542	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	656	905
Significant Observable Inputs (Level 2) | Municipal
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	7,067	8,257
Significant Observable Inputs (Level 2) | RMBS
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	3,799	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	2,449	2,169
Significant Unobservable Inputs (Level 3)
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	2,132	2,404
Fixed maturities, at fair value using the fair value option ("FVO")	193	160
Equity securities, at fair value	60	64
Derivative assets	0	1
Short-term investments	60	80
Total assets accounted for at fair value on a recurring basis	2,445	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
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	164	257
Significant Unobservable Inputs (Level 3) | CMBS
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	224	196
Significant Unobservable Inputs (Level 3) | Corporate
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	1,609	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	5	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	130	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