BUSINESS SEGMENT INFORMATION - Operations by Segment - Revenues (Details) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) segment	Sep. 30, 2017 USD ($)
Segment Reporting, Revenue Reconciling Item [Line Items]
Number of Reportable Insurance Business Segments | segment				2
Net earned premiums		$ 4,636	$ 4,648	$ 14,086	$ 13,951
Net investment income		870	811	2,569	2,408
Total adjusted revenues		5,473	5,416	16,557	16,241
Realized investment gains (losses)	[1],[2],[3]	104	90	75	2
Total revenues		5,577	5,506	16,632	16,243
Gain (loss) on change in fair value of derivative, corporate		9		18
Aflac Japan
Segment Reporting, Revenue Reconciling Item [Line Items]
Net earned premiums		3,159	3,200	9,649	9,616
Net investment income, less amortized hedge costs		606	561	1,801	1,676
Other income (loss)		10	11	31	31
Total revenues		3,775	3,772	11,481	11,323
Hedge costs		59	60	168	168
Aflac U.S.
Segment Reporting, Revenue Reconciling Item [Line Items]
Net earned premiums		1,426	1,393	4,280	4,172
Net investment income		187	181	544	539
Other income (loss)		3	1	7	3
Total revenues		1,616	1,575	4,831	4,714
Corporate and other
Segment Reporting, Revenue Reconciling Item [Line Items]
Total revenues		$ 82	$ 69	$ 245	$ 204

[1] Amortized hedge costs related to hedging U.S. dollar-denominated investments held in Aflac Japan were $59 and $60 for the three- month periods and $168 and for both the nine-month periods ended September 30, 2018, and 2017, respectively, and have been reclassified from realized investment gains (losses) and reported as a deduction from net investment income when analyzing segment operations.

[2] Amortized hedge costs in Aflac Japan were partially offset by derivatives entered into as part of corporate activities and resulted in a benefit of $9 for the three-month period and $18 for the nine-month period ended September 30, 2018, respectively, which has been reclassified from realized investment gains (losses) and reported as an increase in net investment income when analyzing operations.

[3] An immaterial amount of net interest cash flows from derivatives associated with certain investment strategies in the three- and nine-month periods ended September 30, 2018, were reclassified from realized investment gains (losses) into net investment income when analyzing operations.