BENEFIT PLANS - Fair Value Hierarchy Levels of Funded Pension Plans' Assets (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Japan Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	$ 229	$ 198	$ 183
U.S. Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	359	336	$ 341
U.S. Pension Plan | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	359	336
Japanese equity securities | Japan Pension Plan | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	28	22
International equity securities | Japan Pension Plan | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	40	33
Japanese bonds | Japan Pension Plan | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	79	71
International bonds | Japan Pension Plan | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	55	48
Insurance contracts | Japan Pension Plan | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	27	23
Cash and cash equivalents | Japan Pension Plan | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0	1
Cash and cash equivalents | U.S. Pension Plan | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	1	1
U S large cap equity securities | U.S. Pension Plan | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	104	94
U S mid cap equity securities | U.S. Pension Plan | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	19	16
Real estate equity funds | U.S. Pension Plan | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	10	10
International fund | U.S. Pension Plan | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	85	77
Fixed income funds | U.S. Pension Plan | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	136	134
Aflac Incorporated common stock | U.S. Pension Plan | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	$ 4	$ 4