BUSINESS SEGMENT INFORMATION - Operations by Segment - Revenues (Details) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) segment	Jun. 30, 2018 USD ($)
Segment Reporting, Revenue Reconciling Item [Line Items]
Number of Reportable Insurance Business Segments | segment				2
Net earned premiums		$ 4,681	$ 4,706	$ 9,373	$ 9,450
Net investment income		878	862	1,756	1,699
Total adjusted revenues		5,528	5,539	11,065	11,084
Realized investment gains (losses)	[1],[2],[3]	(17)	50	103	(30)
Total revenues		5,511	5,589	11,168	11,054
Net interest cash flows from derivatives		(7)		(14)
Aflac Japan
Segment Reporting, Revenue Reconciling Item [Line Items]
Net earned premiums		3,172	3,227	6,352	6,490
Net investment income, less amortized hedge costs		609	606	1,219	1,194
Other income		11	11	22	22
Total revenues		3,792	3,844	7,593	7,706
Hedge costs		62	55	124	110
Aflac U.S.
Segment Reporting, Revenue Reconciling Item [Line Items]
Net earned premiums		1,459	1,426	2,920	2,853
Net investment income		180	182	357	357
Other income		2	2	4	4
Total revenues		1,641	1,610	3,281	3,214
Corporate and other
Segment Reporting, Revenue Reconciling Item [Line Items]
Total revenues		95	85	191	164
Hedge income		$ 20	$ 7	$ 40	$ 9

[1] Amortized hedge costs of $62 and $55 for the three-month periods and $124 and $110 for the six-month periods ended June 30, 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 $7 for the three-month periods and $40 and $9 for the six-month periods ended June 30, 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 and $(14) for the six-month period ended June 30, 2019 and an immaterial amount for the three- and six-month periods in 2018, respectively, have been reclassified from realized investment gains (losses) and included in adjusted earnings as a component of net investment income.