Schedule II - Aflac Incorporated (Parent Only) - Condensed Statements of Comprehensive Income (Loss) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Financial Statements, Captions [Line Items]
Net earnings		$ 4,604	$ 2,659	$ 2,533
Other comprehensive income (loss) before income taxes:
Unrealized foreign currency translation gains (losses) during period		286	283	360
Unrealized gains (losses) on investment securities during period		1,731	2,852	(2,534)
Pension liability adjustment during period		9	(45)	(20)
Total other comprehensive income (loss) before income taxes		2,029	3,040	(2,255)
Income tax expense (benefit) related to items of other comprehensive income (loss)		631	1,035	(901)
Other comprehensive income (loss), net of income taxes	[1]	1,398	2,005	(1,354)
Total comprehensive income (loss)		6,002	4,664	1,179
Parent Company
Condensed Financial Statements, Captions [Line Items]
Net earnings		4,604	2,659	2,533
Other comprehensive income (loss) before income taxes:
Unrealized foreign currency translation gains (losses) during period		286	283	360
Unrealized gains (losses) on investment securities during period		1,733	2,799	(2,595)
Unrealized gains (losses) on derivatives during period		1	3	0
Pension liability adjustment during period		9	(45)	(20)
Total other comprehensive income (loss) before income taxes		2,029	3,040	(2,255)
Income tax expense (benefit) related to items of other comprehensive income (loss)		631	1,035	(901)
Other comprehensive income (loss), net of income taxes		1,398	2,005	(1,354)
Total comprehensive income (loss)		$ 6,002	$ 4,664	$ 1,179

[1] All amounts in the table above are net of tax.