POLICY LIABILITIES - Liability for Future Policy Benefits (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability amounts		$ 81,857	$ 76,106
Aflac Japan
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		3.40%	3.50%	3.60%
Aflac U.S.
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		5.40%	5.50%	5.60%
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]	$ (609)	$ (630)
Health insurance | Aflac Japan | 1992 - 2017
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability amounts		$ 10,167	8,912
Health insurance | Aflac Japan | 1992 - 2017 | 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 - 2017 | 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		$ 1,133	1,118
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 - 2017
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		$ 12,386	11,687
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		$ 2,454	2,485
Health insurance | Aflac Japan | 1994 - 1996
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability amounts		$ 3,046	3,069
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		$ 14,829	14,372
Health insurance | Aflac Japan | 1985 - 1991
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability amounts		$ 1,816	1,871
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		$ 2,037	2,134
Health insurance | Aflac U.S. | 2013 - 2017
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability amounts		$ 82	75
Health insurance | Aflac U.S. | 2013 - 2017 | 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. | 2012 - 2017
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		$ 1,366	1,062
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		$ 343	319
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		$ 2,944	3,004
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		$ 656	669
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		$ 1,296	1,265
Health insurance | Aflac U.S. | 1981 - 1986
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability amounts		$ 159	166
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		$ 1,310	1,295
Health insurance | Aflac U.S. | Other years
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability amounts		18	19
Life insurance | Aflac Japan | 2001 - 2017
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability amounts		$ 8,850	7,255
Life insurance | Aflac Japan | 2001 - 2017 | 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 - 2017 | 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		$ 4,763	4,151
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		$ 3,393	2,861
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		$ 1,642	1,488
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		$ 2,048	2,007
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		$ 1,319	1,220
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		$ 2,189	2,102
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		$ 675	657
Life insurance | Aflac Japan | 1994 - 1996
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability amounts		$ 908	897
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 - 2017
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability amounts		$ 632	$ 571
Life insurance | Aflac U.S. | 1956 - 2017 | 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 - 2017 | 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