FAIR VALUE MEASUREMENTS - Fair Value Inputs Assets Quantitative Information (Details) - USD ($) $ / shares in Units, $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		$ 85,336	$ 76,702
Asset derivatives		331	1,207
Assets, fair value		89,215	$ 83,044
Length of Volatility of Japanese Yen to US Dollar Exchange Rate			10 years
Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		430	$ 242
Asset derivatives		151	127
Assets, fair value		581	369
Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		82,524	73,760
Fixed maturities | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		414	239
Equity securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		1,023	1,309
Equity securities | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		16	3
Equity securities | Net asset value valuation technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		16	3
Equity securities | Net asset value valuation technique | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		16	$ 3
Equity securities | Assets | Lower Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Offered Quotes			$ 1
Equity securities | Assets | Upper Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Offered Quotes			701
Equity securities | Assets | Weighted Average | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Offered Quotes			$ 8
Mortgage- and asset-backed securities | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		444	$ 1,337
Mortgage- and asset-backed securities | Fixed maturities | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		175	198
Mortgage- and asset-backed securities | Fixed maturities | Consensus pricing valuation technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		175	198
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		175	198
Public utilities | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		7,954	7,683
Public utilities | Fixed maturities | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		68	16
Public utilities | Fixed maturities | Discounted cash flow valuation technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		68	16
Public utilities | Fixed maturities | Discounted cash flow valuation technique | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		68	16
Banks/financial institutions | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		7,377	6,063
Banks/financial institutions | Fixed maturities | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		25	25
Banks/financial institutions | Fixed maturities | Consensus pricing valuation technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		25	25
Banks/financial institutions | Fixed maturities | Consensus pricing valuation technique | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		25	25
Other corporate | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		32,240	29,699
Other corporate | Fixed maturities | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		146	0
Other corporate | Fixed maturities | Discounted cash flow valuation technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		146
Other corporate | Fixed maturities | Discounted cash flow valuation technique | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		146
Foreign currency swaps
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Asset derivatives		296	490
Foreign currency swaps | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Asset derivatives		150	125
Credit default swaps
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Asset derivatives		1	2
Credit default swaps | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Asset derivatives		1	2
Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY), CDS Spreads and Foreign Exchange Rates | Foreign currency swaps | Discounted cash flow valuation technique | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Asset derivatives			$ 16
Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY), CDS Spreads and Foreign Exchange Rates | Foreign currency swaps | Assets | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Foreign Exchange Rates	[1]		21.47%
Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY), CDS Spreads and Foreign Exchange Rates | Foreign currency swaps | Assets | Lower Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Entity Credit Risk			0.17%
Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY), CDS Spreads and Foreign Exchange Rates | Foreign currency swaps | Assets | Upper Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Entity Credit Risk			1.72%
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		$ 80	$ 29
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		0.09%	0.16%
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		0.90%	0.88%
Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY) and Foreign Exchange Rates | Foreign currency swaps | Discounted cash flow valuation technique | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Asset derivatives			$ 80
Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY) and Foreign Exchange Rates | Foreign currency swaps | Assets | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Foreign Exchange Rates	[1]		21.47%
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		$ 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	$ 2
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		0.25%	0.54%
Fair Value Inputs, Recovery Rate		37.24%	36.69%
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	[2]	46.33%	52.18%
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	[2]	49.65%	56.07%
Yen-denominated | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		$ 43,896	$ 37,149
Yen-denominated | Equity securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		695	705
Yen-denominated | Mortgage- and asset-backed securities | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		271	1,121
Yen-denominated | Public utilities | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		1,981	1,848
Yen-denominated | Banks/financial institutions | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		4,019	3,002
Yen-denominated | Other corporate | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		$ 4,654	$ 3,812
Yen-denominated | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY), CDS Spreads and Foreign Exchange Rates | Foreign currency swaps | Assets | Lower Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[3]		0.22%
Yen-denominated | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY), CDS Spreads and Foreign Exchange Rates | Foreign currency swaps | Assets | Upper Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[3]		0.80%
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	[3]	0.26%	0.22%
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	[3]	0.85%	0.80%
Yen-denominated | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY) and Foreign Exchange Rates | Foreign currency swaps | Assets | Lower Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[3]		0.22%
Yen-denominated | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY) and Foreign Exchange Rates | Foreign currency swaps | Assets | Upper Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[3]		0.80%
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	[3]	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	[3]	0.85%
Dollar-denominated | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		$ 38,628	$ 36,611
Dollar-denominated | Equity securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		328	604
Dollar-denominated | Mortgage- and asset-backed securities | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		173	216
Dollar-denominated | Public utilities | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		5,973	5,835
Dollar-denominated | Banks/financial institutions | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		3,358	3,061
Dollar-denominated | Other corporate | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		$ 27,586	$ 25,887
Dollar-denominated | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY), CDS Spreads and Foreign Exchange Rates | Foreign currency swaps | Assets | Lower Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[4]		2.34%
Dollar-denominated | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY), CDS Spreads and Foreign Exchange Rates | Foreign currency swaps | Assets | Upper Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[4]		2.59%
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	[4]	2.40%	2.34%
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	[4]	2.54%	2.59%
Dollar-denominated | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY) and Foreign Exchange Rates | Foreign currency swaps | Assets | Lower Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[4]		2.34%
Dollar-denominated | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY) and Foreign Exchange Rates | Foreign currency swaps | Assets | Upper Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[4]		2.59%
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	[4]	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	[4]	2.54%

[1] Based on 10 year volatility of JPY/USD exchange rate

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

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

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