FAIR VALUE MEASUREMENTS - Fair Value Measurement Inputs and Valuation Techniques (Details) $ in Millions		Sep. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		$ 93,940	$ 82,895
Equity securities		830	987
Asset derivatives		411	417
Liability derivatives		403	387
Assets, fair value		100,119	88,788
Liabilities, fair value		403	387
Level 3
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		636	522
Equity securities		79	46
Asset derivatives		147	182
Assets, fair value		862	750
Liabilities, fair value		139	102
Net asset value valuation technique
Fair Value Measurement Inputs and Valuation Techniques
Equity securities		79	46
Net asset value valuation technique | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Equity securities		79	46
Foreign currency swaps
Fair Value Measurement Inputs and Valuation Techniques
Asset derivatives		227	285
Liability derivatives		227	234
Foreign currency swaps | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Asset derivatives		147	182
Liability derivatives		139	102
Foreign currency swaps | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY) and CDS Spreads | Discounted cash flow technique | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Asset derivatives		81	125
Liability derivatives		132	98
Foreign currency swaps | Fair Value, Unobservable Input, Interest Rates (USD) and Interest Rates (JPY) | Discounted cash flow technique | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Asset derivatives		66	57
Liability derivatives		$ 7	$ 4
Foreign currency swaps | Credit Spread | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY) and CDS Spreads | Lower Limit | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Derivative asset, measurement input		0.0012	0.0019
Derivative liability, measurement input		0.0022	0.0028
Foreign currency swaps | Credit Spread | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY) and CDS Spreads | Upper Limit | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Derivative asset, measurement input		0.0106	0.0120
Derivative liability, measurement input		0.0176	0.0211
Dollar-denominated
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		$ 38,890	$ 33,995
Equity securities		$ 202	$ 346
Dollar-denominated | Foreign currency swaps | Discount Rate | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY) and CDS Spreads | Lower Limit | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Derivative asset, measurement input	[1]	0.0143	0.0275
Derivative liability, measurement input	[1]	0.0143	0.0275
Dollar-denominated | Foreign currency swaps | Discount Rate | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY) and CDS Spreads | Upper Limit | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Derivative asset, measurement input	[1]	0.0163	0.0284
Derivative liability, measurement input	[1]	0.0163	0.0284
Dollar-denominated | Foreign currency swaps | Discount Rate | Fair Value, Unobservable Input, Interest Rates (USD) and Interest Rates (JPY) | Lower Limit | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Derivative asset, measurement input	[1]	0.0143	0.0275
Derivative liability, measurement input	[1]	0.0143	0.0275
Dollar-denominated | Foreign currency swaps | Discount Rate | Fair Value, Unobservable Input, Interest Rates (USD) and Interest Rates (JPY) | Upper Limit | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Derivative asset, measurement input	[1]	0.0163	0.0284
Derivative liability, measurement input	[1]	0.0163	0.0284
Yen-denominated
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		$ 55,050	$ 48,900
Equity securities		$ 628	$ 641
Yen-denominated | Foreign currency swaps | Discount Rate | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY) and CDS Spreads | Lower Limit | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Derivative asset, measurement input	[2]	(0.0003)	0.0018
Derivative liability, measurement input	[2]	(0.0003)	0.0018
Yen-denominated | Foreign currency swaps | Discount Rate | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY) and CDS Spreads | Upper Limit | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Derivative asset, measurement input	[2]	0.0032	0.0071
Derivative liability, measurement input	[2]	0.0032	0.0071
Yen-denominated | Foreign currency swaps | Discount Rate | Fair Value, Unobservable Input, Interest Rates (USD) and Interest Rates (JPY) | Lower Limit | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Derivative asset, measurement input	[2]	(0.0003)	0.0018
Derivative liability, measurement input	[2]	(0.0003)	0.0018
Yen-denominated | Foreign currency swaps | Discount Rate | Fair Value, Unobservable Input, Interest Rates (USD) and Interest Rates (JPY) | Upper Limit | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Derivative asset, measurement input	[2]	0.0032	0.0071
Derivative liability, measurement input	[2]	0.0032	0.0071
Mortgage- and asset-backed securities
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		$ 409	$ 339
Mortgage- and asset-backed securities | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		183	177
Mortgage- and asset-backed securities | Consensus pricing valuation technique
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		183	177
Mortgage- and asset-backed securities | Consensus pricing valuation technique | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		183	177
Mortgage- and asset-backed securities | Dollar-denominated
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		146	162
Mortgage- and asset-backed securities | Yen-denominated
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		263	177
Banks/financial institutions
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		10,644	8,918
Banks/financial institutions | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		23	23
Banks/financial institutions | Consensus pricing valuation technique
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		69	23
Banks/financial institutions | Consensus pricing valuation technique | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		23	23
Banks/financial institutions | Dollar-denominated
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		3,664	3,214
Banks/financial institutions | Yen-denominated
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		6,980	5,704
Public utilities
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		6,950	7,171
Public utilities | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		206	109
Public utilities | Discounted cash flow technique
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		206	109
Public utilities | Discounted cash flow technique | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		206	109
Public utilities | Dollar-denominated
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		4,691	5,163
Public utilities | Yen-denominated
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		2,259	2,008
Other corporate
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		34,659	29,002
Other corporate | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		224	213
Other corporate | Discounted cash flow technique
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		227	213
Other corporate | Discounted cash flow technique | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		224	213
Other corporate | Dollar-denominated
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		28,463	23,545
Other corporate | Yen-denominated
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		$ 6,196	$ 5,457

[1] Inputs derived from U.S. long-term rates to accommodate long maturity nature of the Company's swaps

[2] Inputs derived from Japan long-term rates to accommodate long maturity nature of the Company's swaps