FAIR VALUE MEASUREMENTS - Fair Value Hierarchy Levels of Assets by Pricing Source, Securities Carried at Amortized Cost (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	$ 38,822	$ 36,722
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	28,868	27,030
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	9,943	9,677
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	11	15
Government and agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	29,234	27,038
Government and agencies | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	28,868	27,030
Government and agencies | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	366	8
Government and agencies | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	0	0
Government and agencies | Third party pricing vendor valuation technique
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	29,234	27,038
Government and agencies | Third party pricing vendor valuation technique | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	28,868	27,030
Government and agencies | Third party pricing vendor valuation technique | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	366	8
Government and agencies | Third party pricing vendor valuation technique | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	0	0
Municipalities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	1,114	469
Municipalities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	0	0
Municipalities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	1,114	469
Municipalities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	0	0
Municipalities | Third party pricing vendor valuation technique
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	1,114	469
Municipalities | Third party pricing vendor valuation technique | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	0	0
Municipalities | Third party pricing vendor valuation technique | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	1,114	469
Municipalities | Third party pricing vendor valuation technique | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	0	0
Mortgage- and asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	19	15
Mortgage- and asset-backed securities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	0	0
Mortgage- and asset-backed securities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	8	0
Mortgage- and asset-backed securities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	11	15
Mortgage- and asset-backed securities | Third party pricing vendor valuation technique
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	8
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]
Held to maturity, fixed maturity securities, fair value	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]
Held to maturity, fixed maturity securities, fair value	8
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]
Held to maturity, fixed maturity securities, fair value	0
Mortgage- and asset-backed securities | Consensus pricing valuation technique
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	11	15
Mortgage- and asset-backed securities | Consensus pricing valuation technique | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	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]
Held to maturity, fixed maturity securities, fair value	0	0
Mortgage- and asset-backed securities | Consensus pricing valuation technique | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	11	15
Public utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	2,967	2,973
Public utilities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	0	0
Public utilities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	2,967	2,973
Public utilities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	0	0
Public utilities | Third party pricing vendor valuation technique
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	2,967	2,973
Public utilities | Third party pricing vendor valuation technique | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	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]
Held to maturity, fixed maturity securities, fair value	2,967	2,973
Public utilities | Third party pricing vendor valuation technique | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	0	0
Sovereign and supranational
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	1,384	1,840
Sovereign and supranational | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	0	0
Sovereign and supranational | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	1,384	1,840
Sovereign and supranational | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	0	0
Sovereign and supranational | Third party pricing vendor valuation technique
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	1,384	1,840
Sovereign and supranational | Third party pricing vendor valuation technique | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	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]
Held to maturity, fixed maturity securities, fair value	1,384	1,840
Sovereign and supranational | Third party pricing vendor valuation technique | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	0	0
Banks/financial institutions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	1,030	1,583
Banks/financial institutions | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	0	0
Banks/financial institutions | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	1,030	1,583
Banks/financial institutions | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	0	0
Banks/financial institutions | Third party pricing vendor valuation technique
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	1,030	1,583
Banks/financial institutions | Third party pricing vendor valuation technique | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	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]
Held to maturity, fixed maturity securities, fair value	1,030	1,583
Banks/financial institutions | Third party pricing vendor valuation technique | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	0	0
Other corporate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	3,074	2,804
Other corporate | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	0	0
Other corporate | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	3,074	2,804
Other corporate | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	0	0
Other corporate | Third party pricing vendor valuation technique
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	3,074	2,804
Other corporate | Third party pricing vendor valuation technique | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	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]
Held to maturity, fixed maturity securities, fair value	3,074	2,804
Other corporate | Third party pricing vendor valuation technique | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held to maturity, fixed maturity securities, fair value	$ 0	$ 0