FAIR VALUE MEASUREMENTS - Fair Value Measurement Inputs and Valuation Techniques (Details) $ in Millions		Dec. 31, 2018 USD ($)		Dec. 31, 2017 USD ($)
Fair Value Measurement Inputs and Valuation Technique
Available for sale, fixed maturity securities	[2],[3]	$ 82,895	[1],[4]	$ 84,313	[5]
Equity securities	[2],[3],[6]	987
Equity securities, available-for-sale				1,023
Asset derivatives		417		331
Liability derivatives		387		474
Assets, fair value		88,788		89,215
Liabilities, fair value		387		474
Level 3
Fair Value Measurement Inputs and Valuation Technique
Available for sale, fixed maturity securities		522		414
Equity securities		46
Equity securities, available-for-sale				16
Asset derivatives		182		151
Assets, fair value		750		581
Liabilities, fair value		102		128
Net asset value valuation technique
Fair Value Measurement Inputs and Valuation Technique
Equity securities		46
Equity securities, available-for-sale				16
Net asset value valuation technique | Level 3
Fair Value Measurement Inputs and Valuation Technique
Equity securities		46
Equity securities, available-for-sale				16
Foreign currency swaps
Fair Value Measurement Inputs and Valuation Technique
Asset derivatives		285		296
Liability derivatives		234		197
Foreign currency swaps | Level 3
Fair Value Measurement Inputs and Valuation Technique
Asset derivatives		182		150
Liability derivatives		102		128
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 Technique
Asset derivatives		125		80
Liability derivatives		98		120
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 Technique
Asset derivatives		57		70
Liability derivatives		$ 4		$ 8
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 Technique
Derivative asset, measurement input		0.0019		0.0009
Derivative liability, measurement input		0.0028		0.0013
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 Technique
Derivative asset, measurement input		0.0120		0.0090
Derivative liability, measurement input		0.0211		0.0157
Credit default swaps
Fair Value Measurement Inputs and Valuation Technique
Asset derivatives				$ 1
Credit default swaps | Level 3
Fair Value Measurement Inputs and Valuation Technique
Asset derivatives				1
Credit default swaps | Fair value, Unobservable Input, Base Correlation, CDS Spreads, Recovery Rate | Discounted cash flow technique | Level 3
Fair Value Measurement Inputs and Valuation Technique
Asset derivatives				$ 1
Credit default swaps | Credit Spread | Fair value, Unobservable Input, Base Correlation, CDS Spreads, Recovery Rate | Level 3
Fair Value Measurement Inputs and Valuation Technique
Derivative asset, measurement input				0.0025
Credit default swaps | Base Correlation | Fair value, Unobservable Input, Base Correlation, CDS Spreads, Recovery Rate | Lower Limit | Level 3
Fair Value Measurement Inputs and Valuation Technique
Derivative asset, measurement input	[7]			0.4633
Credit default swaps | Base Correlation | Fair value, Unobservable Input, Base Correlation, CDS Spreads, Recovery Rate | Upper Limit | Level 3
Fair Value Measurement Inputs and Valuation Technique
Derivative asset, measurement input	[7]			0.4965
Credit default swaps | Recovery Rate | Fair value, Unobservable Input, Base Correlation, CDS Spreads, Recovery Rate | Level 3
Fair Value Measurement Inputs and Valuation Technique
Derivative asset, measurement input				0.3724
Dollar-denominated
Fair Value Measurement Inputs and Valuation Technique
Available for sale, fixed maturity securities		$ 33,995		$ 38,703
Equity securities		$ 346
Equity securities, available-for-sale				$ 328
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 Technique
Derivative asset, measurement input	[8]	0.0275		0.0240
Derivative liability, measurement input	[8]	0.0275		0.0240
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 Technique
Derivative asset, measurement input	[8]	0.0284		0.0254
Derivative liability, measurement input	[8]	0.0284		0.0254
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 Technique
Derivative asset, measurement input	[8]	0.0275		0.0240
Derivative liability, measurement input	[8]	0.0275		0.0240
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 Technique
Derivative asset, measurement input	[8]	0.0284		0.0254
Derivative liability, measurement input	[8]	0.0284		0.0254
Yen-denominated
Fair Value Measurement Inputs and Valuation Technique
Available for sale, fixed maturity securities		$ 48,900		$ 45,610
Equity securities		$ 641
Equity securities, available-for-sale				$ 695
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 Technique
Derivative asset, measurement input	[9]	0.0018		0.0026
Derivative liability, measurement input	[9]	0.0018		0.0026
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 Technique
Derivative asset, measurement input	[9]	0.0071		0.0085
Derivative liability, measurement input	[9]	0.0071		0.0085
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 Technique
Derivative asset, measurement input	[9]	0.0018		0.0026
Derivative liability, measurement input	[9]	0.0018		0.0026
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 Technique
Derivative asset, measurement input	[9]	0.0071		0.0085
Derivative liability, measurement input	[9]	0.0071		0.0085
Mortgage- and asset-backed securities
Fair Value Measurement Inputs and Valuation Technique
Available for sale, fixed maturity securities		$ 339		$ 444
Mortgage- and asset-backed securities | Level 3
Fair Value Measurement Inputs and Valuation Technique
Available for sale, fixed maturity securities		177		175
Mortgage- and asset-backed securities | Consensus pricing valuation technique
Fair Value Measurement Inputs and Valuation Technique
Available for sale, fixed maturity securities		177		175
Mortgage- and asset-backed securities | Consensus pricing valuation technique | Level 3
Fair Value Measurement Inputs and Valuation Technique
Available for sale, fixed maturity securities		177		175
Mortgage- and asset-backed securities | Dollar-denominated
Fair Value Measurement Inputs and Valuation Technique
Available for sale, fixed maturity securities		162		173
Mortgage- and asset-backed securities | Yen-denominated
Fair Value Measurement Inputs and Valuation Technique
Available for sale, fixed maturity securities		177		271
Banks/financial institutions
Fair Value Measurement Inputs and Valuation Technique
Available for sale, fixed maturity securities		8,918		8,933
Banks/financial institutions | Level 3
Fair Value Measurement Inputs and Valuation Technique
Available for sale, fixed maturity securities		23		25
Banks/financial institutions | Consensus pricing valuation technique
Fair Value Measurement Inputs and Valuation Technique
Available for sale, fixed maturity securities		23		25
Banks/financial institutions | Consensus pricing valuation technique | Level 3
Fair Value Measurement Inputs and Valuation Technique
Available for sale, fixed maturity securities		23		25
Banks/financial institutions | Dollar-denominated
Fair Value Measurement Inputs and Valuation Technique
Available for sale, fixed maturity securities		3,214		3,433
Banks/financial institutions | Yen-denominated
Fair Value Measurement Inputs and Valuation Technique
Available for sale, fixed maturity securities		5,704		5,500
Public utilities
Fair Value Measurement Inputs and Valuation Technique
Available for sale, fixed maturity securities		7,171		7,954
Public utilities | Level 3
Fair Value Measurement Inputs and Valuation Technique
Available for sale, fixed maturity securities		109		68
Public utilities | Discounted cash flow technique
Fair Value Measurement Inputs and Valuation Technique
Available for sale, fixed maturity securities		109		68
Public utilities | Discounted cash flow technique | Level 3
Fair Value Measurement Inputs and Valuation Technique
Available for sale, fixed maturity securities		109		68
Public utilities | Dollar-denominated
Fair Value Measurement Inputs and Valuation Technique
Available for sale, fixed maturity securities		5,163		5,973
Public utilities | Yen-denominated
Fair Value Measurement Inputs and Valuation Technique
Available for sale, fixed maturity securities		2,008		1,981
Other corporate
Fair Value Measurement Inputs and Valuation Technique
Available for sale, fixed maturity securities		29,002		32,473
Other corporate | Level 3
Fair Value Measurement Inputs and Valuation Technique
Available for sale, fixed maturity securities		213		146
Other corporate | Discounted cash flow technique
Fair Value Measurement Inputs and Valuation Technique
Available for sale, fixed maturity securities		213		146
Other corporate | Discounted cash flow technique | Level 3
Fair Value Measurement Inputs and Valuation Technique
Available for sale, fixed maturity securities		213		146
Other corporate | Dollar-denominated
Fair Value Measurement Inputs and Valuation Technique
Available for sale, fixed maturity securities		23,545		27,586
Other corporate | Yen-denominated
Fair Value Measurement Inputs and Valuation Technique
Available for sale, fixed maturity securities		$ 5,457		$ 4,887

[1] Includes perpetual securities ($1,139 at amortized cost and $1,140 at fair value)

[2] Includes perpetual securities

[3] Includes perpetual securities

[4] Includes perpetual securities, categorized in accordance with their respective economic maturities (the expected maturity date created by the combination of features in the financial instrument)

[5] Includes perpetual securities ($1,462 at amortized cost and $1,789 at fair value)

[6] Includes perpetual securities ($62 at fair value)

[7] Range of base correlation for the Company's bespoke tranche for attachment and detachment points corresponding to market indices

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

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