BUSINESS SEGMENT INFORMATION - Operations by Segment - Revenues (Details) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) segment	Sep. 30, 2016 USD ($)
Segment Reporting, Revenue Reconciling Item [Line Items]
Number of Reportable Insurance Business Segments | segment				2
Net earned premiums		$ 4,648	$ 5,022	$ 13,951	$ 14,447
Net investment income		811	842	2,408	2,465
Total revenues		5,506	5,716	16,243	16,604
Total operating revenues		5,435	5,846	16,300	16,902
Realized investment gains (losses), non-operating	[1],[2],[3],[4],[5],[6]	71	(130)	(57)	(298)
Gain (loss) on change in fair value of derivative, interest rate component, operating		19	20	60	64
Aflac Japan
Segment Reporting, Revenue Reconciling Item [Line Items]
Net earned premiums		3,200	3,596	9,616	10,177
Net investment income, less amortized hedge costs	[1]	561	607	1,676	1,802
Other income (loss)		11	10	31	29
Total revenues		3,772	4,213	11,323	12,008
Hedge costs		60	54	168	123
Aflac U.S.
Segment Reporting, Revenue Reconciling Item [Line Items]
Net earned premiums		1,393	1,365	4,172	4,093
Other income (loss)		1	1	3	5
Net investment income		181	176	539	526
Total revenues		1,575	1,542	4,714	4,624
Other business segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total revenues		69	71	204	207
Total Business Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total revenues		5,416	5,826	16,241	16,839
Corporate and eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Total revenues		$ 19	$ 20	$ 59	$ 63

[1] Amortized hedge costs related to hedging U.S. dollar-denominated investments held in Aflac Japan were $60 and $54 for the three-month periods and $168 and $123 for the nine-month periods ended September 30, 2017, and 2016, respectively, and have been reclassified from realized investment gains (losses) and reported as a deduction from net investment income when analyzing segment operations to conform to current year reporting.

[2] Amortized hedge costs related to hedging U.S. dollar-denominated investments held in Aflac Japan were $60 and $54 for the three-month periods and $168 and $123 for the nine-month periods ended September 30, 2017, and 2016, respectively, and have been reclassified from realized investment gains (losses) and reported as a deduction from pretax operating earnings when analyzing segment operations to conform to current year reporting.

[3] Excluding a gain of $19 and $20 for the three-month periods and $60 and $64 for the nine-month periods ended September 30, 2017, and 2016, respectively, related to the interest rate component of the change in fair value of foreign currency swaps on notes payable which is classified as an operating gain when analyzing segment operations

[4] Excluding a gain of $19 and $20 for the three-month periods and $60 and $64 for the nine-month periods ended September 30, 2017, and 2016, respectively, related to the interest rate component of the change in fair value of foreign currency swaps on notes payable which is classified as an operating gain when analyzing segment operations

[5] Prior year foreign currency transaction gains and losses have been reclassified from other non-operating income (loss) to realized investment gains (losses) to conform to current-year reporting classifications. These reclassifications had no impact on total earnings before income taxes.

[6] Prior year foreign currency transaction gains and losses have been reclassified from other non-operating income (loss) to realized investment gains (losses) to conform to current-year reporting classifications. These reclassifications had no impact on total revenues