BENEFIT PLANS - Fair Value Hierarchy Levels of Funded Pension Plans' Assets (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Japanese Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	$ 187	$ 171	$ 147
Japanese Pension Plan | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	187	171
Japanese Pension Plan | Level 2 | Domestic Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	15	11
Japanese Pension Plan | Level 2 | International Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	42	34
Japanese Pension Plan | Level 2 | Japanese bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	62	60
Japanese Pension Plan | Level 2 | International Bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	44	42
Japanese Pension Plan | Level 2 | Insurance Contracts
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	24	24
U.S. Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	261	224	209
U.S. Pension Plan | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	261	224
U.S. Pension Plan | Level 1 | US Large Cap Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	87	77
U.S. Pension Plan | Level 1 | US Mid Cap
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	16	13
U.S. Pension Plan | Level 1 | Real Estate Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	8	7
U.S. Pension Plan | Level 1 | International Fund
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	59	45
U.S. Pension Plan | Level 1 | Fixed Income Bond Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	88	79
U.S. Pension Plan | Level 1 | Aflac Incorporated Common Stock
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	$ 3	$ 3