Schedule II - Aflac Incorporated (Parent Only) - Condensed Statements of Comprehensive Income (Loss) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Financial Statements, Captions [Line Items]
Net earnings		$ 2,920	$ 4,604	$ 2,659
Other comprehensive income (loss) before income taxes:
Unrealized foreign currency translation gains (losses) during period		232	286	283
Unrealized gains (losses) on derivatives during period		2	1	3
Pension liability adjustment during period		(25)	9	(45)
Total other comprehensive income (loss) before income taxes		(2,900)	2,029	3,040
Income tax expense (benefit) related to items of other comprehensive income (loss)		(797)	631	1,035
Other comprehensive income (loss), net of tax	[1]	(2,103)	1,398	2,005
Total comprehensive income (loss)		817	6,002	4,664
Parent Company
Condensed Financial Statements, Captions [Line Items]
Net earnings		2,920	4,604	2,659
Other comprehensive income (loss) before income taxes:
Unrealized foreign currency translation gains (losses) during period		232	286	283
Unrealized gains (losses) on fixed maturity securities during period	[2]	(3,109)	1,733	2,799
Unrealized gains (losses) on derivatives during period		2	1	3
Pension liability adjustment during period		(25)	9	(45)
Total other comprehensive income (loss) before income taxes		(2,900)	2,029	3,040
Income tax expense (benefit) related to items of other comprehensive income (loss)		(797)	631	1,035
Other comprehensive income (loss), net of tax		(2,103)	1,398	2,005
Total comprehensive income (loss)		$ 817	$ 6,002	$ 4,664

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

[2] See Note 1 of the Notes to the Consolidated Financial Statements for the adoption of accounting guidance on January 1, 2018 related to financial instruments.