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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Additional Information (Detail) $ in Millions |  | 9 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | ---
Jan. 01, 2021 USD ($) | Sep. 30, 2023 USD ($) segment | Sep. 30, 2022 USD ($) | Jun. 30, 2023 USD ($) | Dec. 31, 2022 USD ($) | Jun. 30, 2022 USD ($) | Dec. 31, 2021 USD ($)
Significant Accounting Policies [Line Items] |  |  |  |  |  |  |
Number of reportable insurance business segments | segment |  | 2 |  |  |  |  |
Accumulated other comprehensive income (loss) |  | $ (5,760) | $ (7,505) | $ (7,338) | $ (6,429) | $ (6,980) | $ (8,411)
Retained earnings |  | $ 48,257 |  |  | $ 44,367 |  |
Accounting Standards Update 2018-12 |  |  |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |  |  |
Capped transition date NPR | 100.00% |  |  |  |  |  |
Accounting Standards Update 2018-12 | Cumulative Effect, Period of Adoption, Adjustment |  |  |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |  |  |
Accumulated other comprehensive income (loss) | $ (18,600) |  |  |  |  |  |
Retained earnings | $ (300) |  |  |  |  |  |
Aflac Japan |  |  |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |  |  |
Percentage of the Company's total revenues |  | 63.00% | 72.00% |  |  |  |
Percentage of the Company's total assets |  | 79.00% |  |  | 80.00% |  |

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