BENEFIT PLANS - Fair Value Hierarchy Levels of Funded Pension Plans' Assets (Detail) - Pension Plan - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Japan
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	$ 415	$ 416	$ 344
U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	885	824	$ 644
Japanese equity securities | Japan | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	21	20
International equity securities | Japan | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	86	88
Japanese bonds | Japan | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	22	23
International bonds | Japan | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	252	249
Insurance contracts | Japan | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	34	36
U.S. large cap equity securities | U.S. | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	297	234
U.S. mid cap equity securities | U.S. | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	25	24
Real estate equity funds | U.S. | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0	19
International equity funds | U.S. | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	208	136
Fixed income bond funds | U.S. | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	346	237
Aflac Incorporated common stock | U.S. | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	7	5
Cash and cash equivalents | U.S. | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	$ 2	$ 169