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Summary of Significant Accounting Policies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified | 12 Months Ended | 3 Months Ended |  | 12 Months Ended | 3 Months Ended
--- | --- | --- | --- | --- | ---
Dec. 31, 2010 Accounting Standards Update 2010-26 | Mar. 31, 2012 Aflac Japan | Mar. 31, 2011 Aflac Japan | Dec. 31, 2011 Aflac Japan | Dec. 31, 2010 Retained earnings: Accounting Standards Update 2010-26 | Dec. 31, 2010 Accumulated Other Comprehensive Income (Loss) Accounting Standards Update 2010-26 | Mar. 31, 2012 Dollar denominated investment portfolio [Member] Aflac Japan | Mar. 31, 2011 Dollar denominated investment portfolio [Member] Aflac Japan
Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |
Aflac Japan's percentage of the Company's total revenues |  | 77.00% | 74.00% |  |  |  |  |
Aflac Japan's percentage of the Company's total assets |  | 87.00% |  | 87.00% |  |  |  |
Other comprehensive income foreign exchange gains or losses, deferred tax expense (benefit) |  |  |  |  |  |  | $ 157 | $ 51
Effective income tax rate excluding income tax expense (benefit) related to Aflac Japan's dollar-denominated portfolio |  |  |  |  |  |  | 44.50% | 32.40%
Adjustment to the shareholders' equity upon adoption of new DAC accounting guidance | $ (516) |  |  |  | $ (408) | $ (108) |  |

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