Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.

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Period Type:	instant

Summary of Significant Accounting Policies - Additional Information (Detail) $ in Millions	9 Months Ended
	Sep. 30, 2021 USD ($) segment	Sep. 30, 2020 USD ($)	Jun. 30, 2021 USD ($)	Jan. 01, 2021 USD ($)	Dec. 31, 2020 USD ($)	Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Significant Accounting Policies [Line Items]
Number of reportable insurance business segments \| segment	2
Accumulated other comprehensive income (loss)	$ 7,662	$ 7,917	$ 8,019		$ 8,934	$ 6,750	$ 6,615
Lower Limit \| Pro Forma \| Accounting Standards Update 2018-12 \| Cumulative effect, period of adoption, adjustment
Significant Accounting Policies [Line Items]
Accumulated other comprehensive income (loss)				$ (18,000)
Upper Limit \| Pro Forma \| Accounting Standards Update 2018-12 \| Cumulative effect, period of adoption, adjustment
Significant Accounting Policies [Line Items]
Accumulated other comprehensive income (loss)				$ (20,000)
Aflac Japan
Significant Accounting Policies [Line Items]
Percentage of the Company's total revenues	69.00%	68.00%
Percentage of the Company's total assets	82.00%				83.00%