BUSINESS SEGMENT INFORMATION - Operations by Segment - Revenues (Details) $ in Millions		3 Months Ended
		Mar. 31, 2018 USD ($) segment	Mar. 31, 2017 USD ($)
Segment Reporting, Revenue Reconciling Item [Line Items]
Number of Reportable Insurance Business Segments | segment		2
Net earned premiums		$ 4,745	$ 4,638
Net investment income		837	794
Total adjusted revenues		5,546	5,397
Realized investment gains (losses)	[1],[2]	(82)	(88)
Total revenues		5,464	5,309
Gain (loss) on change in fair value of derivative, corporate		2
Aflac Japan
Segment Reporting, Revenue Reconciling Item [Line Items]
Net earned premiums		3,263	3,194
Net investment income, less amortized hedge costs	[2]	588	557
Other income (loss)		12	10
Total revenues		3,863	3,761
Hedge costs		55	52
Aflac U.S.
Segment Reporting, Revenue Reconciling Item [Line Items]
Net earned premiums		1,427	1,390
Net investment income		175	178
Other income (loss)		2	1
Total revenues		1,604	1,569
Corporate and other
Segment Reporting, Revenue Reconciling Item [Line Items]
Total revenues	[1]	$ 79	$ 67

[1] Amortized hedge costs in Aflac Japan were offset by derivatives entered into as part of corporate activities and resulted in a benefit of $2 for the three-month period ended March 31, 2018 which has been reclassified from realized investment gains (losses) and reported as an increase in net investment income when analyzing operations.

[2] Amortized hedge costs related to hedging U.S. dollar-denominated investments held in Aflac Japan were $55 and $52 for the three-month periods ended March 31, 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.