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Summary of Significant Accounting Policies - Additional Information (Detail)
$ in Millions
3 Months Ended
Mar. 31, 2022
USD ($)
segment
Mar. 31, 2021
USD ($)
Dec. 31, 2021
USD ($)
Jan. 01, 2021
USD ($)
Dec. 31, 2020
USD ($)
Significant Accounting Policies [Line Items]          
Number of reportable insurance business segments | segment 2        
Accumulated other comprehensive income (loss) $ 3,113 $ 6,807 $ 7,393   $ 8,934
Retained earnings $ 42,413   $ 41,381    
Pro Forma | Accounting Standards Update 2018-12 | Cumulative effect, period of adoption, adjustment          
Significant Accounting Policies [Line Items]          
Retained earnings       $ (300)  
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 71.00% 70.00%      
Percentage of the Company's total assets 81.00%   82.00%