BUSINESS SEGMENT INFORMATION - Operations by Segment - Revenues (Details) $ in Millions		3 Months Ended
		Mar. 31, 2019 USD ($) segment	Mar. 31, 2018 USD ($)
Segment Reporting, Revenue Reconciling Item [Line Items]
Number of Reportable Insurance Business Segments | segment		2
Net earned premiums		$ 4,691	$ 4,745
Net investment income		878	837
Total adjusted revenues		5,537	5,546
Realized investment gains (losses)	[1],[2],[3]	120	(82)
Total revenues		5,657	5,464
Net interest cash flows from derivatives		(7)
Aflac Japan
Segment Reporting, Revenue Reconciling Item [Line Items]
Net earned premiums		3,180	3,263
Net investment income, less amortized hedge costs		610	588
Other income (loss)		12	12
Total revenues		3,802	3,863
Hedge costs		62	55
Aflac U.S.
Segment Reporting, Revenue Reconciling Item [Line Items]
Net earned premiums		1,461	1,427
Net investment income		177	175
Other income (loss)		2	2
Total revenues		1,640	1,604
Corporate and other
Segment Reporting, Revenue Reconciling Item [Line Items]
Total revenues		95	79
Hedge income		$ 20	$ 2

[1] Amortized hedge costs of $62 and $55 for the three-month periods ended March 31, 2019, and 2018, respectively, related to certain foreign currency exposure management strategies have been reclassified from realized investment gains (losses) and reported as a deduction from net investment income when analyzing operations.

[2] Amortized hedge income of $20 and $2 for the three-month periods ended March 31, 2019, and 2018, respectively, related to certain foreign currency exposure management strategies has been reclassified from realized investment gains (losses) and reported as an increase to net investment income when analyzing operations.

[3] Net interest cash flows from derivatives associated with certain investment strategies of $(7) for the three-month period ended March 31, 2019 and an immaterial amount in 2018, respectively, have been reclassified from realized investment gains (losses) and included in adjusted earnings as a component of net investment income.