Fair Value Measurements - Fair Value by Hierarchy (Details) - USD ($) $ in Millions	Jun. 30, 2023	Dec. 31, 2022
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	$ 37,497	$ 36,231
Fixed maturities, at fair value using the fair value option ("FVO")	320	333
Equity securities, at fair value	895	1,801
Derivative assets	6	34
Short-term investments	3,236	3,859
Total assets accounted for at fair value on a recurring basis	41,954	42,258
Liabilities accounted for at fair value on a recurring basis
Derivative liabilities	(41)	13
Total liabilities accounted for at fair value on a recurring basis	(41)	13
Credit derivatives
Assets accounted for at fair value on a recurring basis
Derivative assets		2
Liabilities accounted for at fair value on a recurring basis
Derivative liabilities	(71)	(2)
Foreign exchange derivatives
Assets accounted for at fair value on a recurring basis
Derivative assets	5	32
Liabilities accounted for at fair value on a recurring basis
Derivative liabilities	33	21
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	(3)	(6)
Asset backed securities ("ABS")
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	2,685	1,941
Collateralized Loan Obligations [Member]
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	2,981	2,941
Fixed maturities, at fair value using the fair value option ("FVO")	163	178
CMBS
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	3,227	3,368
Corporate
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	16,096	15,233
Foreign government/government agencies
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	539	547
Municipal
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	6,226	6,296
RMBS
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	3,729	3,708
U.S. Treasuries
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	2,014	2,197
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	0
Fixed maturities, at fair value using the fair value option ("FVO")	0	0
Equity securities, at fair value	357	1,261
Derivative assets	0	0
Short-term investments	1,749	1,429
Total assets accounted for at fair value on a recurring basis	2,106	2,690
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
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	0
Significant Observable Inputs (Level 2)
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	35,483	34,180
Fixed maturities, at fair value using the fair value option ("FVO")	157	155
Equity securities, at fair value	479	479
Derivative assets	6	34
Short-term investments	1,301	2,237
Total assets accounted for at fair value on a recurring basis	37,426	37,085
Liabilities accounted for at fair value on a recurring basis
Derivative liabilities	(41)	13
Total liabilities accounted for at fair value on a recurring basis	(41)	13
Significant Observable Inputs (Level 2) | Credit derivatives
Assets accounted for at fair value on a recurring basis
Derivative assets		2
Liabilities accounted for at fair value on a recurring basis
Derivative liabilities	(71)	(2)
Significant Observable Inputs (Level 2) | Foreign exchange derivatives
Assets accounted for at fair value on a recurring basis
Derivative assets	5	32
Liabilities accounted for at fair value on a recurring basis
Derivative liabilities	33	21
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	(3)	(6)
Significant Observable Inputs (Level 2) | Asset backed securities ("ABS")
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	2,685	1,911
Significant Observable Inputs (Level 2) | Collateralized Loan Obligations [Member]
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	2,896	2,826
Significant Observable Inputs (Level 2) | CMBS
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	2,989	3,146
Significant Observable Inputs (Level 2) | Corporate
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	14,474	13,644
Significant Observable Inputs (Level 2) | Foreign government/government agencies
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	539	547
Significant Observable Inputs (Level 2) | Municipal
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	6,226	6,296
Significant Observable Inputs (Level 2) | RMBS
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	3,660	3,613
Significant Observable Inputs (Level 2) | U.S. Treasuries
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	2,014	2,197
Significant Unobservable Inputs (Level 3)
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	2,014	2,051
Fixed maturities, at fair value using the fair value option ("FVO")	163	178
Equity securities, at fair value	59	61
Derivative assets	0	0
Short-term investments	186	193
Total assets accounted for at fair value on a recurring basis	2,422	2,483
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
Significant Unobservable Inputs (Level 3) | Credit 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) | 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
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	30
Significant Unobservable Inputs (Level 3) | Collateralized Loan Obligations [Member]
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	85	115
Significant Unobservable Inputs (Level 3) | CMBS
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	238	222
Significant Unobservable Inputs (Level 3) | Corporate
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	1,622	1,589
Significant Unobservable Inputs (Level 3) | Foreign government/government agencies
Assets accounted for at fair value on a recurring basis
Debt Securities, Available-for-sale	0	0
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	69	95
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