FAIR VALUE MEASUREMENTS - Fair Value Measurement Inputs and Valuation Techniques (Details) $ in Millions		Jun. 30, 2018 USD ($)		Dec. 31, 2017 USD ($)
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities	[1]	$ 85,881	[2],[3]	$ 84,313	[4]
Available for sale securities, equity securities				1,023
Equity securities	[1],[5]	1,103
Asset derivatives		457		331
Liability derivatives		367		474
Assets, fair value disclosure		91,289		89,215
Liabilities, fair value disclosure		367		474
Level 3
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		503		414
Equity securities		17
Asset derivatives		202		151
Assets, fair value disclosure		722		581
Liabilities, fair value disclosure		92		128
Net asset value valuation technique
Fair Value Measurement Inputs and Valuation Techniques
Equity securities		67
Net asset value valuation technique | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Available for sale securities, equity securities				16
Equity securities		17
Foreign currency swaps
Fair Value Measurement Inputs and Valuation Techniques
Asset derivatives		321		296
Liability derivatives		227		197
Foreign currency swaps | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Asset derivatives		202		150
Liability derivatives		92		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 Techniques
Asset derivatives		145		80
Liability derivatives		88		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 Techniques
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 Techniques
Derivative asset, measurement input		0.0015		0.0009
Derivative liability, measurement input		0.0034		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 Techniques
Derivative asset, measurement input		0.0105		0.0090
Derivative liability, measurement input		0.0188		0.0157
Credit default swaps
Fair Value Measurement Inputs and Valuation Techniques
Asset derivatives				$ 1
Credit default swaps | Level 3
Fair Value Measurement Inputs and Valuation Techniques
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 Techniques
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 Techniques
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 Techniques
Derivative asset, measurement input	[6]			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 Techniques
Derivative asset, measurement input	[6]			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 Techniques
Derivative asset, measurement input				0.3724
Dollar-denominated
Fair Value Measurement Inputs and Valuation Techniques
Available for sale securities, equity securities				$ 328
Equity securities		$ 391
Dollar-denominated | Foreign currency swaps | Discount Rate | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY) and CDS Spreads | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Derivative asset, measurement input	[7]	0.0292
Derivative liability, measurement input	[7]	0.0292
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	[7]			0.0240
Derivative liability, measurement input	[7]			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 Techniques
Derivative asset, measurement input	[7]			0.0254
Derivative liability, measurement input	[7]			0.0254
Dollar-denominated | Foreign currency swaps | Discount Rate | Fair Value, Unobservable Input, Interest Rates (USD) and Interest Rates (JPY) | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Derivative asset, measurement input	[7]	0.0292
Derivative liability, measurement input	[7]	0.0292
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	[7]			0.0240
Derivative liability, measurement input	[7]			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 Techniques
Derivative asset, measurement input	[7]			0.0254
Derivative liability, measurement input	[7]			0.0254
Yen-denominated
Fair Value Measurement Inputs and Valuation Techniques
Available for sale securities, equity securities				$ 695
Equity securities		$ 712
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	[8]	0.0025		0.0026
Derivative liability, measurement input	[8]	0.0025		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 Techniques
Derivative asset, measurement input	[8]	0.0075		0.0085
Derivative liability, measurement input	[8]	0.0075		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 Techniques
Derivative asset, measurement input	[8]	0.0025		0.0026
Derivative liability, measurement input	[8]	0.0025		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 Techniques
Derivative asset, measurement input	[8]	0.0075		0.0085
Derivative liability, measurement input	[8]	0.0075		0.0085
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		$ 175
Banks/financial institutions | Consensus pricing valuation technique | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		23		25
Public utilities | Discounted cash flow technique | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		106		68
Other corporate | Discounted cash flow technique | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		$ 196		$ 146

[1] Includes perpetual securities

[2] Includes perpetual securities ($1,446 at amortized cost and $1,612 at fair value)

[3] 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)

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

[5] Includes perpetual securities ($69 at fair value)

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

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

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