FAIR VALUE MEASUREMENTS - Fair Value Measurement Inputs and Valuation Techniques (Details) $ in Millions		Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		$ 100,744	$ 105,882
Equity securities		1,174	1,283
Asset derivatives		841	583
Liability derivatives		1,094	697
Assets, fair value		109,044	114,028
Liabilities, fair value		1,094	697
Level 3
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		1,098	1,017
Equity securities		122	102
Asset derivatives		138	133
Assets, fair value		1,358	1,252
Liabilities, fair value		218	231
Net asset value valuation technique
Fair Value Measurement Inputs and Valuation Techniques
Equity securities		122	102
Net asset value valuation technique | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Equity securities		122	102
Foreign currency swaps
Fair Value Measurement Inputs and Valuation Techniques
Asset derivatives		201	180
Liability derivatives		242	312
Foreign currency swaps | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Asset derivatives		138	133
Liability derivatives		218	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		73	69
Liability derivatives		140	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		$ 78	$ 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		0.0026	0.0022
Derivative liability, measurement input		0.0027	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		0.0127	0.0128
Derivative liability, measurement input		0.0201	0.0140
Dollar-denominated
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		$ 39,806	$ 41,611
Equity securities		$ 405	$ 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]	0.0178	0.0093
Derivative liability, measurement input	[1]	0.0178	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]	0.0220	0.0140
Derivative liability, measurement input	[1]	0.0220	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]	0.0178	0.0093
Derivative liability, measurement input	[1]	0.0178	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]	0.0220	0.0140
Derivative liability, measurement input	[1]	0.0220	0.0112
Yen-denominated
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		$ 60,938	$ 64,271
Equity securities		$ 727	$ 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]	0.0016	0.0005
Derivative liability, measurement input	[2]	0.0016	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]	0.0057	0.0043
Derivative liability, measurement input	[2]	0.0057	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]	0.0016	0.0005
Derivative liability, measurement input	[2]	0.0016	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]	0.0057	0.0043
Derivative liability, measurement input	[2]	0.0057	0.0035
Mortgage- and asset-backed securities
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		$ 1,184	$ 1,038
Mortgage- and asset-backed securities | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		204	224
Mortgage- and asset-backed securities | Consensus pricing valuation technique
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		778	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		204	224
Mortgage- and asset-backed securities | Dollar-denominated
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		844	670
Mortgage- and asset-backed securities | Yen-denominated
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		340	368
Public utilities
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		10,199	10,817
Public utilities | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		479	422
Public utilities | Discounted cash flow technique
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		479	422
Public utilities | Discounted cash flow technique | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		479	422
Public utilities | Dollar-denominated
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		4,618	4,945
Public utilities | Yen-denominated
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		5,581	5,872
Sovereign and supranational
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		1,275	1,382
Sovereign and supranational | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		68	48
Sovereign and supranational | Discounted cash flow technique
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		68	48
Sovereign and supranational | Discounted cash flow technique | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		68	48
Sovereign and supranational | Dollar-denominated
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		284	293
Sovereign and supranational | Yen-denominated
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		991	1,089
Banks/financial institutions
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		11,575	12,060
Banks/financial institutions | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		28	24
Banks/financial institutions | Consensus pricing valuation technique
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		28	24
Banks/financial institutions | Consensus pricing valuation technique | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		28	24
Banks/financial institutions | Dollar-denominated
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		3,653	3,724
Banks/financial institutions | Yen-denominated
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		7,922	8,336
Other corporate
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		37,819	40,217
Other corporate | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		319	299
Other corporate | Discounted cash flow technique
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		319	331
Other corporate | Discounted cash flow technique | Level 3
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		319	299
Other corporate | Dollar-denominated
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		28,825	30,393
Other corporate | Yen-denominated
Fair Value Measurement Inputs and Valuation Techniques
Available for sale, fixed maturity securities		$ 8,994	$ 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