Schedule II - Aflac Incorporated (Parent Only) - Condensed Statements of Comprehensive Income (Loss) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Financial Statements, Captions [Line Items]
Net earnings	$ 3,304	$ 2,920	$ 4,604
Other comprehensive income (loss) before income taxes:
Unrealized foreign currency translation gains (losses) during period	252	232	286
Unrealized gains (losses) on derivatives during period	(12)	2	1
Pension liability adjustment during period	(85)	(25)	9
Total other comprehensive income (loss) before income taxes	6,007	(2,900)	2,029
Income tax expense (benefit) related to items of other comprehensive income (loss)	1,543	(797)	631
Other comprehensive income (loss), net of tax	4,464	(2,103)	1,398
Total comprehensive income (loss)	7,768	817	6,002
Parent Company
Condensed Financial Statements, Captions [Line Items]
Net earnings	3,304	2,920	4,604
Other comprehensive income (loss) before income taxes:
Unrealized foreign currency translation gains (losses) during period	252	232	286
Unrealized gains (losses) on fixed maturity securities during period	5,852	(3,109)	1,733
Unrealized gains (losses) on derivatives during period	(12)	2	1
Pension liability adjustment during period	(85)	(25)	9
Total other comprehensive income (loss) before income taxes	6,007	(2,900)	2,029
Income tax expense (benefit) related to items of other comprehensive income (loss)	1,543	(797)	631
Other comprehensive income (loss), net of tax	4,464	(2,103)	1,398
Total comprehensive income (loss)	$ 7,768	$ 817	$ 6,002