FAIR VALUE MEASUREMENTS - Fair Value Inputs Assets Quantitative Information (Details) - USD ($) $ / shares in Units, $ in Millions		9 Months Ended	12 Months Ended
		Sep. 30, 2017	Dec. 31, 2016
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		$ 83,206	$ 76,702
Asset derivatives		479	1,207
Assets, fair value		$ 88,669	$ 83,044
Length of Volatility of Japanese Yen to US Dollar Exchange Rate		10 years	10 years
Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		$ 400	$ 242
Asset derivatives		148	127
Assets, fair value		548	369
Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		80,415	73,760
Fixed maturities | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		382	239
Perpetual securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		1,863	1,633
Perpetual securities | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		0	0
Equity securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		928	1,309
Equity securities | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		18	3
Equity securities | Net asset value valuation technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		18	3
Equity securities | Net asset value valuation technique | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		$ 18	$ 3
Equity securities | Assets | Lower Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Offered Quotes		$ 1	$ 1
Equity securities | Assets | Upper Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Offered Quotes		724	701
Equity securities | Assets | Weighted Average | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Offered Quotes		$ 6	$ 8
Mortgage- and asset-backed securities | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		$ 456	$ 1,337
Mortgage- and asset-backed securities | Fixed maturities | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		178	198
Mortgage- and asset-backed securities | Fixed maturities | Consensus pricing valuation technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		178	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		178	198
Public utilities | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		8,015	7,683
Public utilities | Fixed maturities | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		77	16
Public utilities | Fixed maturities | Discounted cash flow valuation technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		77	16
Public utilities | Fixed maturities | Discounted cash flow valuation technique | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		77	16
Banks/financial institutions | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		7,010	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
Banks/financial institutions | Perpetual securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		1,627	1,420
Banks/financial institutions | Perpetual securities | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		0	0
Other corporate | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		31,575	29,699
Other corporate | Fixed maturities | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		102	0
Other corporate | Fixed maturities | Discounted cash flow valuation technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		102
Other corporate | Fixed maturities | Discounted cash flow valuation technique | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		102
Other corporate | Perpetual securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		236	213
Other corporate | Perpetual securities | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		0	0
Foreign currency swaps
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Asset derivatives		301	490
Foreign currency swaps | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Asset derivatives		147	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		$ 27	$ 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]	21.00%	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		0.11%	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		1.16%	1.72%
Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY), and CDS Spread | Foreign currency swaps | Discounted cash flow valuation technique | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Asset derivatives		$ 45	$ 29
Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY), and CDS Spread | Foreign currency swaps | Assets | Lower Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Entity Credit Risk		0.11%	0.16%
Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY), and CDS Spread | Foreign currency swaps | Assets | Upper Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Entity Credit Risk		0.83%	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		$ 75	$ 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]	21.00%	21.47%
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		0.19%	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]	62.73%	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]	66.88%	56.07%
Dollar-denominated | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		$ 38,017	$ 36,611
Dollar-denominated | Equity securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		280	604
Dollar-denominated | Mortgage- and asset-backed securities | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		179	216
Dollar-denominated | Public utilities | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		6,010	5,835
Dollar-denominated | Banks/financial institutions | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		3,268	3,061
Dollar-denominated | Banks/financial institutions | Perpetual securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		74	75
Dollar-denominated | Other corporate | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		$ 27,018	$ 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	[3]	2.29%	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	[3]	2.53%	2.59%
Dollar-denominated | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY), and CDS Spread | Foreign currency swaps | Assets | Lower Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[3]	2.29%	2.34%
Dollar-denominated | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY), and CDS Spread | Foreign currency swaps | Assets | Upper Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[3]	2.53%	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	[3]	2.29%	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	[3]	2.53%	2.59%
Yen-denominated | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		$ 42,398	$ 37,149
Yen-denominated | Equity securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		648	705
Yen-denominated | Mortgage- and asset-backed securities | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		277	1,121
Yen-denominated | Public utilities | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		2,005	1,848
Yen-denominated | Banks/financial institutions | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		3,742	3,002
Yen-denominated | Banks/financial institutions | Perpetual securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		1,553	1,345
Yen-denominated | Other corporate | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		4,557	3,812
Yen-denominated | Other corporate | Perpetual securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		$ 236	$ 213
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	[4]	0.26%	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	[4]	0.86%	0.80%
Yen-denominated | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY), and CDS Spread | Foreign currency swaps | Assets | Lower Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[4]	0.26%	0.22%
Yen-denominated | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY), and CDS Spread | Foreign currency swaps | Assets | Upper Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[4]	0.86%	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	[4]	0.26%	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	[4]	0.86%	0.80%

[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 U.S. long-term rates to accommodate long maturity nature of the Company's swaps

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