Schedule II - Aflac Incorporated (Parent Only) - Condensed Statements of Comprehensive Income (Loss) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Condensed Financial Statements, Captions [Line Items]
Net earnings	$ 4,778	$ 3,304	$ 2,920
Other comprehensive income (loss) before income taxes:
Unrealized foreign currency translation gains (losses) during period	510	252	232
Unrealized gains (losses) on derivatives during period	(1)	(12)	2
Pension liability adjustment during period	(7)	(85)	(25)
Total other comprehensive income (loss) before income taxes	1,722	6,007	(2,900)
Income tax expense (benefit) related to items of other comprehensive income (loss)	251	1,543	(797)
Other comprehensive income (loss), net of tax	1,471	4,464	(2,103)
Total comprehensive income (loss)	6,249	7,768	817
Parent Company
Condensed Financial Statements, Captions [Line Items]
Net earnings	4,778	3,304	2,920
Other comprehensive income (loss) before income taxes:
Unrealized foreign currency translation gains (losses) during period	510	252	232
Unrealized gains (losses) on fixed maturity securities during period	1,220	5,852	(3,109)
Unrealized gains (losses) on derivatives during period	(1)	(12)	2
Pension liability adjustment during period	(7)	(85)	(25)
Total other comprehensive income (loss) before income taxes	1,722	6,007	(2,900)
Income tax expense (benefit) related to items of other comprehensive income (loss)	251	1,543	(797)
Other comprehensive income (loss), net of tax	1,471	4,464	(2,103)
Total comprehensive income (loss)	$ 6,249	$ 7,768	$ 817