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REINSURANCE Effect of Reinsurance on Premiums and Benefits and Claims (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Effects of Reinsurance [Line Items]
Direct premium income									$ 18,955	$ 19,122	$ 19,018
Ceded premiums									(553)	(547)	(555)
Assumed premiums earned									220	205	214
Net premium income	$ 4,653	$ 4,623	$ 4,664	$ 4,681	$ 4,671	$ 4,736	$ 4,681	$ 4,691	18,622	18,780	18,677
Direct benefits and claims									12,080	12,237	12,293
Benefits and claims, net									11,796	11,942	12,000
Intercompany eliminations
Effects of Reinsurance [Line Items]
Ceded benefits and claims									39	41	43
Assumed benefits and claims from other companies									(39)	(41)	(53)
All other
Effects of Reinsurance [Line Items]
Ceded premiums									(87)	(69)	(58)
Assumed premiums earned									25	5	6
Ceded benefits and claims									(63)	(57)	(44)
Assumed benefits and claims from other companies									18	1	2
Aflac Japan
Effects of Reinsurance [Line Items]
Net premium income									12,670	12,772	12,762
Benefits and claims, net									8,851	8,877	8,913
Aflac Japan \| Closed block
Effects of Reinsurance [Line Items]
Ceded premiums									(466)	(478)	(497)
Assumed premiums earned									195	200	208
Ceded benefits and claims									(419)	(433)	(450)
Assumed benefits and claims from other companies									$ 180	$ 194	$ 209