POLICY LIABILITIES - Liability for Future Policy Benefits (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability amounts		$ 86,368	$ 81,857
Aflac Japan
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		3.30%	3.40%	3.50%
Aflac U.S.
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		5.30%	5.40%	5.50%
Intercompany eliminations | 2015
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		2.00%
Interest Rates In 20 Years		2.00%
Liability amounts	[1]	$ (583)	$ (609)
Health insurance | Aflac Japan | 1992 - 2018
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability amounts		$ 11,598	10,167
Health insurance | Aflac Japan | 1992 - 2018 | Lower Limit
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		1.00%
Interest Rates In 20 Years		1.00%
Health insurance | Aflac Japan | 1992 - 2018 | Upper Limit
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		2.50%
Interest Rates In 20 Years		2.50%
Health insurance | Aflac Japan | 1974 - 2013
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability amounts		$ 1,161	1,133
Health insurance | Aflac Japan | 1974 - 2013 | Lower Limit
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		2.70%
Interest Rates In 20 Years		2.25%
Health insurance | Aflac Japan | 1974 - 2013 | Upper Limit
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		2.75%
Interest Rates In 20 Years		2.75%
Health insurance | Aflac Japan | 1998 - 2018
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		3.00%
Interest Rates In 20 Years		3.00%
Liability amounts		$ 12,764	12,386
Health insurance | Aflac Japan | 1997 - 1999
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		3.50%
Interest Rates In 20 Years		3.50%
Liability amounts		$ 2,452	2,454
Health insurance | Aflac Japan | 1994 - 1996
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability amounts		$ 3,056	3,046
Health insurance | Aflac Japan | 1994 - 1996 | Lower Limit
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		4.00%
Interest Rates In 20 Years		4.00%
Health insurance | Aflac Japan | 1994 - 1996 | Upper Limit
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		4.50%
Interest Rates In 20 Years		4.50%
Health insurance | Aflac Japan | 1987 - 1994
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		5.50%
Interest Rates In 20 Years		5.50%
Liability amounts		$ 14,722	14,829
Health insurance | Aflac Japan | 1985 - 1991
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability amounts		$ 1,779	1,816
Health insurance | Aflac Japan | 1985 - 1991 | Lower Limit
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		5.25%
Interest Rates In 20 Years		5.25%
Health insurance | Aflac Japan | 1985 - 1991 | Upper Limit
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		6.75%
Interest Rates In 20 Years		5.50%
Health insurance | Aflac Japan | 1978 - 1984
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		6.50%
Interest Rates In 20 Years		5.50%
Liability amounts		$ 1,964	2,037
Health insurance | Aflac U.S. | 2013 - 2018
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability amounts		$ 96	82
Health insurance | Aflac U.S. | 2013 - 2018 | Lower Limit
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		3.00%
Interest Rates In 20 Years		3.00%
Health insurance | Aflac U.S. | 2013 - 2018 | Upper Limit
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		3.50%
Interest Rates In 20 Years		3.50%
Health insurance | Aflac U.S. | 2012 - 2018
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		3.75%
Interest Rates In 20 Years		3.75%
Liability amounts		$ 1,682	1,366
Health insurance | Aflac U.S. | 2011
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		4.75%
Interest Rates In 20 Years		4.75%
Liability amounts		$ 353	343
Health insurance | Aflac U.S. | 2005 - 2010
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		5.50%
Interest Rates In 20 Years		5.50%
Liability amounts		$ 2,946	2,944
Health insurance | Aflac U.S. | 1988 - 2004
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		8.00%
Interest Rates In 20 Years		6.00%
Liability amounts		$ 641	656
Health insurance | Aflac U.S. | 1986 - 2004
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		6.00%
Interest Rates In 20 Years		6.00%
Liability amounts		$ 1,245	1,296
Health insurance | Aflac U.S. | 1981 - 1986
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability amounts		$ 151	159
Health insurance | Aflac U.S. | 1981 - 1986 | Lower Limit
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		6.50%
Interest Rates In 20 Years		5.50%
Health insurance | Aflac U.S. | 1981 - 1986 | Upper Limit
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		7.00%
Interest Rates In 20 Years		6.50%
Health insurance | Aflac U.S. | 1998 - 2004
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		7.00%
Interest Rates In 20 Years		7.00%
Liability amounts		$ 1,311	1,310
Health insurance | Aflac U.S. | Other years
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability amounts		17	18
Life insurance | Aflac Japan | 2001 - 2018
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability amounts		$ 10,296	8,850
Life insurance | Aflac Japan | 2001 - 2018 | Lower Limit
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		1.00%
Interest Rates In 20 Years		1.00%
Life insurance | Aflac Japan | 2001 - 2018 | Upper Limit
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		1.85%
Interest Rates In 20 Years		1.85%
Life insurance | Aflac Japan | 2011 - 2017
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		2.00%
Interest Rates In 20 Years		2.00%
Liability amounts		$ 5,116	4,763
Life insurance | Aflac Japan | 2009 - 2011
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		2.25%
Interest Rates In 20 Years		2.25%
Liability amounts		$ 3,867	3,393
Life insurance | Aflac Japan | 1992 - 2006
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		2.19%
Interest Rates In 20 Years		1.55%
Liability amounts		$ 5	5
Life insurance | Aflac Japan | 2005 - 2011
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		2.50%
Interest Rates In 20 Years		2.50%
Liability amounts		$ 1,769	1,642
Life insurance | Aflac Japan | 1985 - 2006
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		2.70%
Interest Rates In 20 Years		2.25%
Liability amounts		$ 2,057	2,048
Life insurance | Aflac Japan | 2007 - 2011
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		2.75%
Interest Rates In 20 Years		2.75%
Liability amounts		$ 1,380	1,319
Life insurance | Aflac Japan | 1999 - 2011
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		3.00%
Interest Rates In 20 Years		3.00%
Liability amounts		$ 2,249	2,189
Life insurance | Aflac Japan | 1996 - 2009
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		3.50%
Interest Rates In 20 Years		3.50%
Liability amounts		$ 678	675
Life insurance | Aflac Japan | 1994 - 1996
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability amounts		$ 901	908
Life insurance | Aflac Japan | 1994 - 1996 | Lower Limit
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		4.00%
Interest Rates In 20 Years		4.00%
Life insurance | Aflac Japan | 1994 - 1996 | Upper Limit
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		4.50%
Interest Rates In 20 Years		4.50%
Life insurance | Aflac U.S. | 1956 - 2018
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability amounts		$ 695	$ 632
Life insurance | Aflac U.S. | 1956 - 2018 | Lower Limit
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		3.50%
Interest Rates In 20 Years		3.50%
Life insurance | Aflac U.S. | 1956 - 2018 | Upper Limit
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		6.00%
Interest Rates In 20 Years		6.00%

[1] Elimination entry necessary due to recapture of a portion of policy liabilities ceded externally, as a result of the reinsurance retrocession transaction as described in Note 8 of the Notes to the Consolidated Financial Statements