FAIR VALUE MEASUREMENTS - Fair Value Hierarchy Levels of Assets by Pricing Source, Securities Carried at Fair Value (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	$ 102,284	$ 105,882
Equity securities	1,475	1,283
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	34,344	36,032
Equity securities	1,231	1,095
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	66,803	68,833
Equity securities	86	86
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	1,137	1,017
Equity securities	158	102
Third party pricing vendor valuation technique
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	1,317	1,181
Third party pricing vendor valuation technique | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	1,231	1,095
Third party pricing vendor valuation technique | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	86	86
Third party pricing vendor valuation technique | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	0	0
Net asset value valuation technique
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	158	102
Net asset value valuation technique | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	0	0
Net asset value valuation technique | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	0	0
Net asset value valuation technique | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	158	102
Government and agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	35,682	37,350
Government and agencies | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	34,344	36,032
Government and agencies | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	1,338	1,318
Government and agencies | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	0	0
Government and agencies | Third party pricing vendor valuation technique
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	35,181	37,350
Government and agencies | Third party pricing vendor valuation technique | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	34,344	36,032
Government and agencies | Third party pricing vendor valuation technique | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	837	1,318
Government and agencies | Third party pricing vendor valuation technique | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	0	0
Government and agencies | Consensus pricing valuation technique
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	501
Government and agencies | Consensus pricing valuation technique | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	0
Government and agencies | Consensus pricing valuation technique | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	501
Government and agencies | Consensus pricing valuation technique | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	0
Municipalities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	2,965	3,018
Municipalities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	0	0
Municipalities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	2,965	3,018
Municipalities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	0	0
Municipalities | Third party pricing vendor valuation technique
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	2,117	3,018
Municipalities | Third party pricing vendor valuation technique | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	0	0
Municipalities | Third party pricing vendor valuation technique | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	2,117	3,018
Municipalities | Third party pricing vendor valuation technique | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	0	0
Municipalities | Consensus pricing valuation technique
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	848
Municipalities | Consensus pricing valuation technique | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	0
Municipalities | Consensus pricing valuation technique | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	848
Municipalities | Consensus pricing valuation technique | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	0
Mortgage- and asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	1,284	1,038
Mortgage- and asset-backed securities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	0	0
Mortgage- and asset-backed securities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	1,026	814
Mortgage- and asset-backed securities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	258	224
Mortgage- and asset-backed securities | Third party pricing vendor valuation technique
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	1,023	364
Mortgage- and asset-backed securities | Third party pricing vendor valuation technique | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	0	0
Mortgage- and asset-backed securities | Third party pricing vendor valuation technique | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	1,023	364
Mortgage- and asset-backed securities | Third party pricing vendor valuation technique | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	0	0
Mortgage- and asset-backed securities | Consensus pricing valuation technique
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	261	674
Mortgage- and asset-backed securities | Consensus pricing valuation technique | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	0	0
Mortgage- and asset-backed securities | Consensus pricing valuation technique | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	3	450
Mortgage- and asset-backed securities | Consensus pricing valuation technique | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	258	224
Public utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	10,393	10,817
Public utilities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	0	0
Public utilities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	9,913	10,395
Public utilities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	480	422
Public utilities | Third party pricing vendor valuation technique
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	4,644	10,395
Public utilities | Third party pricing vendor valuation technique | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	0	0
Public utilities | Third party pricing vendor valuation technique | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	4,644	10,395
Public utilities | Third party pricing vendor valuation technique | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	0	0
Public utilities | Discounted cash flow technique
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	5,749	422
Public utilities | Discounted cash flow technique | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	0	0
Public utilities | Discounted cash flow technique | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	5,269	0
Public utilities | Discounted cash flow technique | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	480	422
Sovereign and supranational
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	1,258	1,382
Sovereign and supranational | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	0	0
Sovereign and supranational | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	1,213	1,334
Sovereign and supranational | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	45	48
Sovereign and supranational | Third party pricing vendor valuation technique
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	286	1,334
Sovereign and supranational | Third party pricing vendor valuation technique | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	0	0
Sovereign and supranational | Third party pricing vendor valuation technique | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	286	1,334
Sovereign and supranational | Third party pricing vendor valuation technique | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	0	0
Sovereign and supranational | Discounted cash flow technique
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	972	48
Sovereign and supranational | Discounted cash flow technique | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	0	0
Sovereign and supranational | Discounted cash flow technique | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	927	0
Sovereign and supranational | Discounted cash flow technique | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	45	48
Banks/financial institutions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	11,904	12,060
Banks/financial institutions | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	0	0
Banks/financial institutions | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	11,866	12,036
Banks/financial institutions | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	38	24
Banks/financial institutions | Third party pricing vendor valuation technique
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	5,243	12,036
Banks/financial institutions | Third party pricing vendor valuation technique | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	0	0
Banks/financial institutions | Third party pricing vendor valuation technique | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	5,243	12,036
Banks/financial institutions | Third party pricing vendor valuation technique | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	0	0
Banks/financial institutions | Consensus pricing valuation technique
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	6,661	24
Banks/financial institutions | Consensus pricing valuation technique | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	0	0
Banks/financial institutions | Consensus pricing valuation technique | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	6,623	0
Banks/financial institutions | Consensus pricing valuation technique | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	38	24
Other corporate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	38,798	40,217
Other corporate | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	0	0
Other corporate | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	38,482	39,918
Other corporate | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	316	299
Other corporate | Third party pricing vendor valuation technique
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	30,184	39,886
Other corporate | Third party pricing vendor valuation technique | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	0	0
Other corporate | Third party pricing vendor valuation technique | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	30,184	39,886
Other corporate | Third party pricing vendor valuation technique | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	0	0
Other corporate | Discounted cash flow technique
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	8,614	331
Other corporate | Discounted cash flow technique | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	0	0
Other corporate | Discounted cash flow technique | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	8,298	32
Other corporate | Discounted cash flow technique | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale, fixed maturity securities	$ 316	$ 299