FAIR VALUE MEASUREMENTS - Fair Value Measurement Inputs and Valuation Techniques (Details) $ in Millions		Sep. 30, 2021 USD ($)	Dec. 31, 2020 USD ($)
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		$ 100,722	$ 105,882
Equity securities		1,461	1,283
Asset derivatives		745	583
Liability derivatives		1,270	697
Assets, fair value		110,969	114,028
Liabilities, fair value		1,270	697
Level 3
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		1,170	1,017
Equity securities		161	102
Asset derivatives		99	133
Assets, fair value		1,430	1,252
Liabilities, fair value		356	231
Net asset value valuation technique
Fair Value Measurement Inputs and Valuation Techniques
Equity securities		161	102
Net asset value valuation technique | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Equity securities		161	102
Foreign currency swaps
Fair Value Measurement Inputs and Valuation Techniques
Asset derivatives		151	180
Liability derivatives		378	312
Foreign currency swaps | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Asset derivatives		99	133
Liability derivatives		356	231
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		34	69
Liability derivatives		167	160
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		65	64
Liability derivatives		$ 189	$ 71
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		0.0023	0.0022
Derivative liability, measurement input		0.0023	0.0041
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		0.0124	0.0128
Derivative liability, measurement input		0.0182	0.0140
Dollar-denominated
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		$ 40,568	$ 41,611
Equity securities		$ 667	$ 603
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	[1]	0.0151	0.0093
Derivative liability, measurement input	[1]	0.0151	0.0093
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	[1]	0.0179	0.0140
Derivative liability, measurement input	[1]	0.0179	0.0112
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	[1]	0.0151	0.0093
Derivative liability, measurement input	[1]	0.0151	0.0093
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	[1]	0.0179	0.0140
Derivative liability, measurement input	[1]	0.0179	0.0112
Yen-denominated
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		$ 60,154	$ 64,271
Equity securities		$ 753	$ 680
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	[2]	0.0011	0.0005
Derivative liability, measurement input	[2]	0.0011	0.0005
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	[2]	0.0053	0.0043
Derivative liability, measurement input	[2]	0.0053	0.0035
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	[2]	0.0011	0.0005
Derivative liability, measurement input	[2]	0.0011	0.0005
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	[2]	0.0053	0.0043
Derivative liability, measurement input	[2]	0.0053	0.0035
Mortgage- and asset-backed securities
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		$ 1,292	$ 1,038
Mortgage- and asset-backed securities | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		250	224
Mortgage- and asset-backed securities | Consensus pricing valuation technique
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		271	674
Mortgage- and asset-backed securities | Consensus pricing valuation technique | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		250	224
Mortgage- and asset-backed securities | Dollar-denominated
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		962	670
Mortgage- and asset-backed securities | Yen-denominated
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		330	368
Public utilities
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		10,315	10,817
Public utilities | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		523	422
Public utilities | Discounted cash flow technique
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		524	422
Public utilities | Discounted cash flow technique | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		523	422
Public utilities | Dollar-denominated
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		4,803	4,945
Public utilities | Yen-denominated
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		5,512	5,872
Sovereign and supranational
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		1,142	1,382
Sovereign and supranational | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		45	48
Sovereign and supranational | Discounted cash flow technique
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		45	48
Sovereign and supranational | Discounted cash flow technique | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		45	48
Sovereign and supranational | Dollar-denominated
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		280	293
Sovereign and supranational | Yen-denominated
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		862	1,089
Banks/financial institutions
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		11,742	12,060
Banks/financial institutions | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		46	24
Banks/financial institutions | Consensus pricing valuation technique
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		46	24
Banks/financial institutions | Consensus pricing valuation technique | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		46	24
Banks/financial institutions | Dollar-denominated
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		3,825	3,724
Banks/financial institutions | Yen-denominated
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		7,917	8,336
Other corporate
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		38,068	40,217
Other corporate | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		306	299
Other corporate | Discounted cash flow technique
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		312	331
Other corporate | Discounted cash flow technique | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		306	299
Other corporate | Dollar-denominated
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		29,138	30,393
Other corporate | Yen-denominated
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		$ 8,930	$ 9,824

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

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