INVESTMENTS - Held-to-Maturity Debt Securities (Details) - USD ($) $ in Millions		Mar. 31, 2020	Dec. 31, 2019
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost		$ 23,287	$ 30,085
Allowance for Credit Loss		9
Net Carrying Amount	[1]	23,278
Gross Unrealized Gains		6,069	7,519
Gross Unrealized Losses		0	10
Fair Value		29,347	37,594
Yen-denominated
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost		23,287	30,085
Allowance for Credit Loss		9
Net Carrying Amount		23,278
Gross Unrealized Gains		6,069	7,519
Gross Unrealized Losses		0	10
Fair Value		29,347	37,594
Japan government and agencies | Yen-denominated
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost		22,387	22,241
Allowance for Credit Loss		3
Net Carrying Amount		22,384
Gross Unrealized Gains		5,810	6,050
Gross Unrealized Losses		0	0
Fair Value		28,194	28,291
Municipalities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost		362	821
Fair Value		484	1,083
Municipalities | Yen-denominated
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost		362	821
Allowance for Credit Loss		0
Net Carrying Amount		362
Gross Unrealized Gains		122	262
Gross Unrealized Losses		0	0
Fair Value		484	1,083
Mortgage- and asset-backed securities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost			16
Fair Value			17
Mortgage- and asset-backed securities | Yen-denominated
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost			16
Gross Unrealized Gains			1
Gross Unrealized Losses			0
Fair Value			17
Public utilities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost		45	2,535
Fair Value		59	2,954
Public utilities | Yen-denominated
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost		46	2,535
Allowance for Credit Loss		1
Net Carrying Amount		45
Gross Unrealized Gains		14	419
Gross Unrealized Losses		0	0
Fair Value		59	2,954
Sovereign and supranational
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost		464	1,123
Fair Value		578	1,320
Sovereign and supranational | Yen-denominated
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost		469	1,123
Allowance for Credit Loss		5
Net Carrying Amount		464
Gross Unrealized Gains		114	197
Gross Unrealized Losses		0	0
Fair Value		578	1,320
Banks/financial institutions
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost			916
Fair Value			1,018
Banks/financial institutions | Yen-denominated
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost			916
Gross Unrealized Gains			105
Gross Unrealized Losses			3
Fair Value			1,018
Other corporate
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost		23	2,433
Fair Value		32	2,911
Other corporate | Yen-denominated
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost		23	2,433
Allowance for Credit Loss		0
Net Carrying Amount		23
Gross Unrealized Gains		9	485
Gross Unrealized Losses		0	7
Fair Value		$ 32	$ 2,911

[1] Net of allowance for credit losses