Schedule II - Aflac Incorporated (Parent Only) - Condensed Balance Sheet (Detail 1) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Investments and cash:
Other investments	[1]	$ 3,402	$ 1,450
Cash and cash equivalents		3,491	4,859	$ 4,350	$ 4,658
Total investments and cash		123,659	116,361
Other assets	[2]	2,023	2,609
Total assets		137,217	129,819	118,256
Liabilities:
Notes payable		5,267	5,339
Other liabilities	[3]	2,832	4,338
Total liabilities		112,619	109,337
Shareholders' equity:
Common stock of $.10 par value. In thousands: authorized 1,900,000 shares in 2017 and 2016; issued 672,881 shares in 2017 and 671,249 shares in 2016		67	67
Additional paid-in capital		2,120	1,976
Retained earnings		29,895	25,981
Accumulated other comprehensive income (loss):
Unrealized foreign currency translation gains (losses)		(1,750)	(1,983)
Unrealized gains (losses) on investment securities		5,964	4,805
Unrealized gains (losses) on derivatives		(23)	(24)
Pension liability adjustment		(163)	(168)
Treasury stock, at average cost		(11,512)	(10,172)
Total shareholders' equity		24,598	20,482	17,708
Total liabilities and shareholders' equity		137,217	129,819
Parent Company
Investments and cash:
Fixed maturity securities available for sale, at fair value (amortized cost $1,163 in 2017 and $483 in 2016)		1,213	496
Investments in subsidiaries	[4]	26,869	23,353
Other investments		51	3
Cash and cash equivalents		1,725	2,037	$ 1,721	$ 1,638
Total investments and cash		29,858	25,889
Due from subsidiaries	[4]	90	75
Income taxes receivable		121	103
Other assets		366	497
Total assets		30,435	26,564
Liabilities:
Employee benefit plans		341	293
Notes payable		5,267	5,339
Other liabilities		229	450
Total liabilities		5,837	6,082
Shareholders' equity:
Common stock of $.10 par value. In thousands: authorized 1,900,000 shares in 2017 and 2016; issued 672,881 shares in 2017 and 671,249 shares in 2016		67	67
Additional paid-in capital		2,120	1,976
Retained earnings		29,895	25,981
Accumulated other comprehensive income (loss):
Unrealized foreign currency translation gains (losses)		(1,750)	(1,983)
Unrealized gains (losses) on investment securities		5,964	4,805
Unrealized gains (losses) on derivatives		(23)	(24)
Pension liability adjustment		(163)	(168)
Treasury stock, at average cost		(11,512)	(10,172)
Total shareholders' equity		24,598	20,482
Total liabilities and shareholders' equity		$ 30,435	$ 26,564

[1] Includes $2,341 in 2017 and $819 in 2016 of loan receivables and limited partnerships from consolidated variable interest entities

[2] Includes $151 in 2017 and $127 in 2016 of derivatives from consolidated variable interest entities

[3] Includes $128 in 2017 and $146 in 2016 of derivatives from consolidated variable interest entities

[4] Eliminated in consolidation