INVESTMENTS - Held-to-Maturity Debt Securities (Details) - USD ($) $ in Millions		Dec. 31, 2020	Dec. 31, 2019
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost		$ 24,474	$ 30,085
Allowance for Credit Losses		10
Net Carrying Amount	[1]	24,464
Gross Unrealized Gains		5,935	7,519
Gross Unrealized Losses		0	10
Fair Value		30,399	37,594
Yen-denominated
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost		24,474	30,085
Allowance for Credit Losses		10
Net Carrying Amount		24,464
Gross Unrealized Gains		5,935	7,519
Gross Unrealized Losses		0	10
Fair Value		30,399	37,594
Japan government and agencies | Yen-denominated
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost		23,448	22,241
Allowance for Credit Losses		3
Net Carrying Amount		23,445
Gross Unrealized Gains		5,625	6,050
Gross Unrealized Losses		0	0
Fair Value		29,070	28,291
Municipalities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost		377	821
Fair Value		499	1,083
Municipalities | Yen-denominated
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost		377	821
Allowance for Credit Losses		0
Net Carrying Amount		377
Gross Unrealized Gains		122	262
Gross Unrealized Losses		0	0
Fair Value		499	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		47	2,535
Fair Value		61	2,954
Public utilities | Yen-denominated
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost		48	2,535
Allowance for Credit Losses		1
Net Carrying Amount		47
Gross Unrealized Gains		14	419
Gross Unrealized Losses		0	0
Fair Value		61	2,954
Sovereign and supranational
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost		571	1,123
Fair Value		736	1,320
Sovereign and supranational | Yen-denominated
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost		577	1,123
Allowance for Credit Losses		6
Net Carrying Amount		571
Gross Unrealized Gains		165	197
Gross Unrealized Losses		0	0
Fair Value		736	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		24	2,433
Fair Value		33	2,911
Other corporate | Yen-denominated
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost		24	2,433
Allowance for Credit Losses		0
Net Carrying Amount		24
Gross Unrealized Gains		9	485
Gross Unrealized Losses		0	7
Fair Value		$ 33	$ 2,911

[1] Net of allowance for credit losses