Schedule II - Aflac Incorporated (Parent Only) - Supplemental Disclosure of Cash Flow Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Schedule of Cash Flow, Supplemental [Line Items]
Interest paid	$ 241	$ 210	$ 178
Shareholder dividend reinvestment
Noncash financing activities:
Treasury stock issued for shareholder dividend reinvestment	26	25	24
Parent Company
Schedule of Cash Flow, Supplemental [Line Items]
Interest paid	241	205	181
Parent Company | Shareholder dividend reinvestment
Noncash financing activities:
Treasury stock issued for shareholder dividend reinvestment	$ 26	$ 25	$ 25