Fair Value Hierarchy Levels of Funded Pension Plans' Assets (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Japanese Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	$ 171	$ 147	$ 114
Japanese Pension Plan | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	171	147
Japanese Pension Plan | Level 2 | Domestic Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	11	11
Japanese Pension Plan | Level 2 | International Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	34	31
Japanese Pension Plan | Level 2 | Japanese bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	60	51
Japanese Pension Plan | Level 2 | International Bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	42	34
Japanese Pension Plan | Level 2 | Insurance Contracts
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	24	20
U.S. Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	224	209	169
U.S. Pension Plan | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	224	209
U.S. Pension Plan | Level 1 | US Large Cap Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	77	75
U.S. Pension Plan | Level 1 | US Mid Cap
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	13	13
U.S. Pension Plan | Level 1 | Real Estate Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	7	6
U.S. Pension Plan | Level 1 | International Fund
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	45	48
U.S. Pension Plan | Level 1 | Fixed Income Bond Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	79	64
U.S. Pension Plan | Level 1 | Aflac Incorporated Common Stock
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	$ 3	$ 3