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Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Millions | 9 Months Ended |
--- | --- | ---
Sep. 30, 2016 | Sep. 30, 2015 | Dec. 31, 2015
Aflac Japan |  |  |
Significant Accounting Policies [Line Items] |  |  |
Aflac Japan's percentage of the Company's total revenues | 74.00% | 70.00% |
Percentage of the Company Assets | 84.00% |  | 83.00%
Lower Limit |  |  |
Significant Accounting Policies [Line Items] |  |  |
New Accounting Pronouncement or Change in Accounting Principle, Estimate, Effect of Adoption on Income Tax Expense (Benefit) | $ (2) |  |
Upper Limit |  |  |
Significant Accounting Policies [Line Items] |  |  |
New Accounting Pronouncement or Change in Accounting Principle, Estimate, Effect of Adoption on Income Tax Expense (Benefit) | $ (11) |  |
Accounting Standards Update 2015-03 |  |  |
Significant Accounting Policies [Line Items] |  |  |
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Assets |  |  | $ (40)
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Liabilities |  |  | $ (40)

X
- Definition New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Assets + References No definition available. + Details
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X
- Definition New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Liabilities + References No definition available. + Details
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- Definition New Accounting Pronouncement or Change in Accounting Principle, Estimate, Effect of Adoption on Income Tax Expense (Benefit) + References No definition available. + Details
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- Definition Significant Accounting Policies [Line Items] + References No definition available. + Details
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- Details
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Balance Type: |
Period Type: |

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- Details
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- Details
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- Details
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