FAIR VALUE MEASUREMENTS - Fair Value Inputs Assets Quantitative Information (Details) - USD ($) $ in Millions		3 Months Ended		12 Months Ended
		Mar. 31, 2018		Dec. 31, 2017
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities	[1]	$ 89,033	[2]	$ 84,313	[3]
Equity securities	[1],[4]	1,108
Asset derivatives		797		331
Assets, fair value		95,018		89,215
Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		436		414
Equity securities		16
Asset derivatives		241		151
Assets, fair value		693		581
Net asset value valuation technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Equity securities		16
Net asset value valuation technique | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Equity securities		16
Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities	[1]	89,033		84,313
Fixed maturities | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		436		414
Equity securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities				1,023
Equity securities | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities				16
Equity securities | Net asset value valuation technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities				16
Equity securities | Net asset value valuation technique | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities				16
Mortgage- and asset-backed securities | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		455		444
Mortgage- and asset-backed securities | Fixed maturities | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		186		175
Mortgage- and asset-backed securities | Fixed maturities | Consensus pricing valuation technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		186		175
Mortgage- and asset-backed securities | Fixed maturities | Consensus pricing valuation technique | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		186		175
Public utilities | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		7,807		7,954
Public utilities | Fixed maturities | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		83		68
Public utilities | Fixed maturities | Discounted cash flow valuation technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		83		68
Public utilities | Fixed maturities | Discounted cash flow valuation technique | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		83		68
Banks/financial institutions | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		9,144		8,933
Banks/financial institutions | Fixed maturities | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		24		25
Banks/financial institutions | Fixed maturities | Consensus pricing valuation technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		24		25
Banks/financial institutions | Fixed maturities | Consensus pricing valuation technique | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		24		25
Other corporate | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		31,652		32,473
Other corporate | Fixed maturities | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		143		146
Other corporate | Fixed maturities | Discounted cash flow valuation technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		143		146
Other corporate | Fixed maturities | Discounted cash flow valuation technique | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		143		146
Foreign currency swaps
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Asset derivatives		370		296
Foreign currency swaps | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Asset derivatives		240		150
Credit default swaps
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Asset derivatives		1		1
Credit default swaps | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Asset derivatives		1		1
Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY) and CDS Spreads | Foreign currency swaps | Discounted cash flow valuation technique | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Asset derivatives		$ 185		$ 80
Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY) and CDS Spreads | Foreign currency swaps | Assets | Lower Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Entity Credit Risk		0.13%		0.09%
Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY) and CDS Spreads | Foreign currency swaps | Assets | Upper Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Entity Credit Risk		1.01%		0.90%
Fair Value, Unobservable Input, Interest Rates (USD) and Interest Rates (JPY) | Foreign currency swaps | Discounted cash flow valuation technique | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Asset derivatives		$ 55		$ 70
Fair Value, Unobservable Input, Base Correlation, CDS Spreads, Recovery Rate | Credit default swaps | Discounted cash flow valuation technique | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Asset derivatives		$ 1		$ 1
Fair Value, Unobservable Input, Base Correlation, CDS Spreads, Recovery Rate | Credit default swaps | Assets | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Entity Credit Risk		0.15%		0.25%
Fair Value Inputs, Recovery Rate		37.24%		37.24%
Fair Value, Unobservable Input, Base Correlation, CDS Spreads, Recovery Rate | Credit default swaps | Assets | Lower Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Base Correlation	[5]	49.98%		46.33%
Fair Value, Unobservable Input, Base Correlation, CDS Spreads, Recovery Rate | Credit default swaps | Assets | Upper Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Base Correlation	[5]	54.13%		49.65%
Dollar-denominated
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Equity securities		$ 397
Dollar-denominated | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		37,233		$ 38,703
Dollar-denominated | Equity securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities				328
Dollar-denominated | Mortgage- and asset-backed securities | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		171		173
Dollar-denominated | Public utilities | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		5,747		5,973
Dollar-denominated | Banks/financial institutions | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		3,264		3,433
Dollar-denominated | Other corporate | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		$ 26,561		$ 27,586
Dollar-denominated | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY) and CDS Spreads | Foreign currency swaps | Assets | Lower Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[6]	2.78%		2.40%
Dollar-denominated | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY) and CDS Spreads | Foreign currency swaps | Assets | Upper Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[6]	2.82%		2.54%
Dollar-denominated | Fair Value, Unobservable Input, Interest Rates (USD) and Interest Rates (JPY) | Foreign currency swaps | Assets | Lower Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[6]	2.78%		2.40%
Dollar-denominated | Fair Value, Unobservable Input, Interest Rates (USD) and Interest Rates (JPY) | Foreign currency swaps | Assets | Upper Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[6]	2.82%		2.54%
Yen-denominated
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Equity securities		$ 711
Yen-denominated | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		51,800		$ 45,610
Yen-denominated | Equity securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities				695
Yen-denominated | Mortgage- and asset-backed securities | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		284		271
Yen-denominated | Public utilities | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		2,060		1,981
Yen-denominated | Banks/financial institutions | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		5,880		5,500
Yen-denominated | Other corporate | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		$ 5,091		$ 4,887
Yen-denominated | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY) and CDS Spreads | Foreign currency swaps | Assets | Lower Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[7]	0.26%		0.26%
Yen-denominated | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY) and CDS Spreads | Foreign currency swaps | Assets | Upper Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[7]	0.85%		0.85%
Yen-denominated | Fair Value, Unobservable Input, Interest Rates (USD) and Interest Rates (JPY) | Foreign currency swaps | Assets | Lower Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[7]	0.26%		0.26%
Yen-denominated | Fair Value, Unobservable Input, Interest Rates (USD) and Interest Rates (JPY) | Foreign currency swaps | Assets | Upper Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[7]	0.85%		0.85%

[1] Includes perpetual securities

[2] Includes perpetual securities ($1,506 at amortized cost and $1,774 at fair value)

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

[4] Includes perpetual securities ($71 at fair value)

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

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

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