FAIR VALUE MEASUREMENTS - Fair Value Measurement Inputs and Valuation Techniques (Details) $ in Millions		Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		$ 87,924	$ 82,895
Equity securities		1,041	987
Asset derivatives		401	417
Liability derivatives		365	387
Assets, fair value		93,801	88,788
Liabilities, fair value		365	387
Level 3
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		570	522
Equity securities		46	46
Asset derivatives		178	182
Assets, fair value		794	750
Liabilities, fair value		108	102
Net asset value valuation technique
Fair Value Measurement Inputs and Valuation Techniques
Equity securities		46	46
Net asset value valuation technique | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Equity securities		46	46
Foreign currency swaps
Fair Value Measurement Inputs and Valuation Techniques
Asset derivatives		274	285
Liability derivatives		206	234
Foreign currency swaps | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Asset derivatives		178	182
Liability derivatives		108	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		117	125
Liability derivatives		102	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		61	57
Liability derivatives		$ 6	$ 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		0.0013	0.0019
Derivative liability, measurement input		0.0030	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		0.0109	0.0120
Derivative liability, measurement input		0.0187	0.0211
Dollar-denominated
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		$ 36,076	$ 33,995
Equity securities		$ 379	$ 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]	0.0248	0.0275
Derivative liability, measurement input	[1]	0.0248	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]	0.0266	0.0284
Derivative liability, measurement input	[1]	0.0266	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]	0.0248	0.0275
Derivative liability, measurement input	[1]	0.0248	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]	0.0266	0.0284
Derivative liability, measurement input	[1]	0.0266	0.0284
Yen-denominated
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		$ 51,848	$ 48,900
Equity securities		$ 662	$ 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]	0.0013	0.0018
Derivative liability, measurement input	[2]	0.0013	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]	0.0057	0.0071
Derivative liability, measurement input	[2]	0.0057	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]	0.0013	0.0018
Derivative liability, measurement input	[2]	0.0013	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]	0.0057	0.0071
Derivative liability, measurement input	[2]	0.0057	0.0071
Mortgage- and asset-backed securities
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		$ 414	$ 339
Mortgage- and asset-backed securities | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		178	177
Mortgage- and asset-backed securities | Consensus pricing valuation technique
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		178	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		178	177
Mortgage- and asset-backed securities | Dollar-denominated
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		154	162
Mortgage- and asset-backed securities | Yen-denominated
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		260	177
Banks/financial institutions
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		9,391	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		68	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		3,269	3,214
Banks/financial institutions | Yen-denominated
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		6,122	5,704
Public utilities
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		6,497	7,171
Public utilities | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		85	109
Public utilities | Discounted cash flow technique
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		85	109
Public utilities | Discounted cash flow technique | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		85	109
Public utilities | Dollar-denominated
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		4,331	5,163
Public utilities | Yen-denominated
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		2,166	2,008
Other corporate
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		32,311	29,002
Other corporate | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		284	213
Other corporate | Discounted cash flow technique
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		347	213
Other corporate | Discounted cash flow technique | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		284	213
Other corporate | Dollar-denominated
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		26,464	23,545
Other corporate | Yen-denominated
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		$ 5,847	$ 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