Aflac (AFL) 10-K 23 Feb 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2017	Feb. 13, 2018	Jun. 30, 2017
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Trading Symbol	AFL
Entity Registrant Name	AFLAC INC
Entity Central Index Key	4,977
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		389,682,983
Entity Public Float			$ 30,514,042,038

Consolidated Statements of Earn

Consolidated Statements of Earnings - USD ($) shares in Thousands, $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues:
Net premiums, principally supplemental health insurance		$ 18,531	$ 19,225	$ 17,570
Net investment income		3,220	3,278	3,135
Realized investment gains (losses):
Other-than-temporary impairment losses realized		(37)	(85)	(154)
Sales and redemptions		28	141	302
Derivative and other gains (losses)		(142)	(70)	(42)
Total realized investment gains (losses)		(151)	(14)	106
Other income (loss)		67	70	61
Total revenues		21,667	22,559	20,872
Benefits and expenses:
Benefits and claims, net		12,181	12,919	11,746
Acquisition and operating expenses:
Amortization of deferred policy acquisition costs		1,132	1,141	1,066
Insurance commissions		1,316	1,368	1,303
Insurance and other expenses	[1]	2,780	2,796	2,606
Interest expense		240	268	289
Total acquisition and operating expenses		5,468	5,573	5,264
Total benefits and expenses		17,649	18,492	17,010
Earnings before income taxes		4,018	4,067	3,862
Income Tax Expense:
Current		631	884	1,288
Deferred		(1,217)	524	41
Total income tax expense		(586)	1,408	1,329
Net earnings		$ 4,604	$ 2,659	$ 2,533
Net earnings per share:
Basic (in dollars per share)		$ 11.63	$ 6.46	$ 5.88
Diluted (in dollars per share)		$ 11.54	$ 6.42	$ 5.85
Weighted-average outstanding common shares used in computing earnings per share (In thousands):
Basic (in shares)		396,021	411,471	430,654
Diluted (in shares)		398,930	413,921	433,172
5.50% subordinated notes due September 2052
Expense on extinguishment of debt		$ 13
Senior Notes due 2039 and 2040
Expense on extinguishment of debt			$ 137
8.50% senior notes due May 2019
Expense on extinguishment of debt				$ 230
[1]	Includes expense of $13 in 2017, $137 in 2016 and $230 in 2015 for the early extinguishment of debt

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net earnings		$ 4,604	$ 2,659	$ 2,533
Other comprehensive income (loss) before income taxes:
Unrealized foreign currency translation gains (losses) during period		286	283	360
Unrealized gains (losses) on investment securities:
Unrealized gains (losses) on investment securities during period		1,731	2,852	(2,534)
Reclassification adjustment for realized (gains) losses on investment securities included in net earnings		2	(53)	(61)
Unrealized gains (losses) on derivatives during period		1	3	0
Pension liability adjustment during period		9	(45)	(20)
Total other comprehensive income (loss) before income taxes		2,029	3,040	(2,255)
Income tax expense (benefit) related to items of other comprehensive income (loss)		631	1,035	(901)
Other comprehensive income (loss), net of income taxes	[1]	1,398	2,005	(1,354)
Total comprehensive income (loss)		$ 6,002	$ 4,664	$ 1,179
[1]	All amounts in the table above are net of tax.

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Securities held to maturity, at amortized cost:
Fixed maturities		$ 31,430	$ 33,350
Other investments	[1]	3,402	1,450
Cash and cash equivalents		3,491	4,859
Total investments and cash		123,659	116,361
Receivables		827	669
Accrued investment income		769	754
Deferred policy acquisition costs		9,505	8,993
Property and equipment, at cost less accumulated depreciation		434	433
Other	[2]	2,023	2,609
Total assets		137,217	129,819
Policy liabilities:
Future policy benefits		81,857	76,106
Unpaid policy claims		4,392	4,045
Unearned premiums		5,959	6,916
Other policyholders' funds		6,939	6,659
Total policy liabilities		99,147	93,726
Income taxes		4,745	5,387
Payables for return of cash collateral on loaned securities		606	526
Notes payable		5,289	5,360
Other	[3]	2,832	4,338
Commitments and contingent liabilities (Note 15)
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
Total liabilities and shareholders' equity		137,217	129,819
Consolidated Entity Excluding Variable Interest Entities (VIE)
Securities available for sale, at fair value:
Fixed maturities		77,230	68,778
Perpetual securities		1,574	1,425
Equity securities		270	265
Securities held to maturity, at amortized cost:
Fixed maturities		31,430	33,350
Variable Interest Entity, Consolidated
Securities available for sale, at fair value:
Fixed maturities		5,294	4,982
Perpetual securities		215	208
Equity securities		753	1,044
Securities held to maturity, at amortized cost:
Other investments	[4]	2,341	819
Policy liabilities:
Total liabilities		$ 128	$ 146
[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]	Consists of TREs, CMLs, MMLs, and alternative investments in limited partnerships

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) shares in Thousands, $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Securities held to maturity, fixed maturities, fair value		$ 38,072	$ 40,021
Common stock, par value (in dollars per share)		$ 0.10	$ 0.10
Common stock, shares authorized (in shares)		1,900,000	1,900,000
Common stock, shares issued (in shares)		672,881	671,249
Asset derivatives		$ 331	$ 1,207
Liability derivatives		474	1,998
Consolidated Entity Excluding Variable Interest Entities (VIE)
Securities available for sale, fixed maturities, amortized cost		69,370	62,195
Securities available for sale, perpetual securities, amortized cost		1,224	1,269
Securities available for sale, equity securities, cost		240	231
Securities held to maturity, fixed maturities, fair value		38,072	40,021
Variable Interest Entity, Consolidated
Securities available for sale, fixed maturities, amortized cost		4,300	4,168
Securities available for sale, perpetual securities, amortized cost		238	237
Securities available for sale, equity securities, cost		606	972
Asset derivatives	[1]	151	127
Liability derivatives	[1]	128	146
Loan receivables and limited partnerships | Variable Interest Entity, Consolidated
Other investments held in unit trust, net of reserves, amortized cost		$ 2,341	$ 819
[1]	Consists entirely of derivatives

Consolidated Statements of Shar

Consolidated Statements of Shareholders' Equity - USD ($) $ in Millions	Total	Common stock:	Additional paid-in capital:	Retained earnings:	Accumulated other comprehensive income (loss):	Treasury stock:
Balance, beginning of period at Dec. 31, 2014		$ 67	$ 1,711	$ 22,156	$ 1,979	$ (7,566)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options			43
Share-based compensation			36
Net earnings	$ 2,533			2,533
Dividends to shareholders ($1.74 per share in 2017, $1.66 per share in 2016 and $1.58 per share in 2015)				(682)
Unrealized foreign currency translation gains (losses) during period, net of income taxes					345
Unrealized gains (losses) on investment securities during the period, net of income taxes and reclassification adjustments					(1,686)
Unrealized gains (losses) on derivatives during period, net of income taxes					0
Pension liability adjustment during period, net of income taxes					(13)
Purchases of treasury stock						(1,315)
Treasury stock reissued			38			62
Balance, end of period at Dec. 31, 2015	17,708	67	1,828	24,007	625	(8,819)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options			46
Share-based compensation			64
Net earnings	2,659			2,659
Dividends to shareholders ($1.74 per share in 2017, $1.66 per share in 2016 and $1.58 per share in 2015)				(685)
Unrealized foreign currency translation gains (losses) during period, net of income taxes					213
Unrealized gains (losses) on investment securities during the period, net of income taxes and reclassification adjustments					1,819
Unrealized gains (losses) on derivatives during period, net of income taxes					2
Pension liability adjustment during period, net of income taxes					(29)
Purchases of treasury stock						(1,422)
Treasury stock reissued			38			69
Balance, end of period at Dec. 31, 2016	20,482	67	1,976	25,981	2,630	(10,172)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options			38
Share-based compensation			51
Net earnings	4,604			4,604
Dividends to shareholders ($1.74 per share in 2017, $1.66 per share in 2016 and $1.58 per share in 2015)				(690)
Unrealized foreign currency translation gains (losses) during period, net of income taxes					233
Unrealized gains (losses) on investment securities during the period, net of income taxes and reclassification adjustments					1,159
Unrealized gains (losses) on derivatives during period, net of income taxes					1
Pension liability adjustment during period, net of income taxes					5
Purchases of treasury stock						(1,391)
Treasury stock reissued			55			51
Balance, end of period at Dec. 31, 2017	$ 24,598	$ 67	$ 2,120	$ 29,895	$ 4,028	$ (11,512)

Consolidated Statements of Sha7

Consolidated Statements of Shareholders' Equity (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2014
Retained earnings:
Dividends to shareholders (in dollars per share)	$ 1.74	$ 1.66	$ 1.58

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016		Dec. 31, 2015
Cash flows from operating activities:
Net earnings	$ 4,604	$ 2,659		$ 2,533
Adjustments to reconcile net earnings to net cash provided by operating activities:
Change in receivables and advance premiums	(91)	42		147
Capitalization of deferred policy acquisition costs	(1,468)	(1,447)		(1,307)
Amortization of deferred policy acquisition costs	1,132	1,141		1,066
Increase in policy liabilities	2,890	3,331		3,524
Change in income tax liabilities	(1,240)	(93)		(36)
Realized investment (gains) losses	151	14		(106)
Other, net	150	340	[1]	955	[1]
Net cash provided (used) by operating activities	6,128	5,987		6,776
Securities available for sale:
Fixed maturities sold	3,819	5,157		3,224
Fixed maturities matured or called	768	1,096		1,132
Perpetual securities matured or called	93	470		647
Equity securities sold	902	350		1
Securities held to maturity:
Fixed maturities matured or called	2,212	1,399		766
Costs of investments acquired:
Available for sale fixed maturities acquired	(9,867)	(10,890)		(6,507)
Available-for-sale equity securities acquired	(446)	(1,079)		(454)
Other investments, net	(2,018)	(1,118)		(70)
Purchase of subsidiary	0	0		(40)
Settlement of derivatives, net	(621)	1,252		(2,119)
Cash received (pledged or returned) as collateral, net	(205)	(416)		(1,391)
Other, net	(68)	(76)		(86)
Net cash provided (used) by investing activities	(5,431)	(3,855)		(4,897)
Cash flows from financing activities:
Purchases of treasury stock	(1,351)	(1,422)		(1,315)
Proceeds from borrowings	1,040	986		998
Principal payments under debt obligations	(1,161)	(610)		(1,272)
Dividends paid to shareholders	(661)	(658)		(656)
Change in investment-type contracts, net	35	159		256
Treasury stock reissued	33	46		36
Other, net	0	(120)	[1]	(234)	[1]
Net cash provided (used) by financing activities	(2,065)	(1,619)		(2,187)
Effect of exchange rate changes on cash and cash equivalents	0	(4)		0
Net change in cash and cash equivalents	(1,368)	509		(308)
Cash and cash equivalents, beginning of period	4,859	4,350		4,658
Cash and cash equivalents, end of period	3,491	4,859		4,350
Supplemental disclosures of cash flow information:
Income taxes paid	780	1,526		996
Interest paid	196	211		236
Noncash interest	44	57		53
Impairment losses included in realized investment losses	37	85		154
Noncash financing activities:
Capitalized lease obligations	12	1		6
Associate stock bonus
Noncash financing activities:
Treasury stock issued	29	30		35
Shareholder dividend reinvestment
Noncash financing activities:
Treasury stock issued	29	27		26
Share-based compensation grants
Noncash financing activities:
Treasury stock issued	$ 1	4		3
Senior Notes due 2039 and 2040
Expense on extinguishment of debt		$ 137
8.50% senior notes due May 2019
Expense on extinguishment of debt				$ 230
[1]	Operating activities excludes and financing activities includes a cash outflow of $137 in 2016 and $230 in 2015 for the payments associated with the early extinguishment of debt

SUMMARY OF SIGNIFICANT ACCOUNTI

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	12 Months Ended
	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Description of Business   Aflac Incorporated (the Parent Company) and its subsidiaries (collectively, the Company) primarily sell supplemental health and life insurance in the United States and Japan. The Company's insurance business is marketed and administered through American Family Life Assurance Company of Columbus (Aflac), which operates in the United States (Aflac U.S.) and as a branch in Japan (Aflac Japan). American Family Life Assurance Company of New York (Aflac New York) is a wholly owned subsidiary of Aflac. Most of Aflac's policies are individually underwritten and marketed through independent agents. Additionally, Aflac U.S. markets and administers group products through Continental American Insurance Company (CAIC), branded as Aflac Group Insurance. The Company's insurance operations in the United States and its branch in Japan service the two markets for the Company's insurance business. Aflac Japan's revenues, including realized gains and losses on its investment portfolio, accounted for 70% of the Company's total revenues in 2017 , compared with 71% in 2016 and 70% in 2015 . The percentage of the Company's total assets attributable to Aflac Japan was 83% at December 31, 2017 and 2016 . Basis of Presentation The Company prepares its financial statements in accordance with U.S. generally accepted accounting principles (GAAP). These principles are established primarily by the Financial Accounting Standards Board (FASB). In these Notes to the Consolidated Financial Statements, references to U.S. GAAP issued by the FASB are derived from the FASB Accounting Standards Codification TM (ASC). The preparation of financial statements in conformity with U.S. GAAP requires the Company to make estimates based on currently available information when recording transactions resulting from business operations. The most significant items on the Company's balance sheet that involve a greater degree of accounting estimates and actuarial determinations subject to changes in the future are the valuation of investments and derivatives, deferred policy acquisition costs (DAC), liabilities for future policy benefits and unpaid policy claims, and income taxes. These accounting estimates and actuarial determinations are sensitive to market conditions, investment yields, mortality, morbidity, commission and other acquisition expenses, and terminations by policyholders. As additional information becomes available, or actual amounts are determinable, the recorded estimates will be revised and reflected in operating results. Although some variability is inherent in these estimates, the Company believes the amounts provided are adequate. The consolidated financial statements include the accounts of the Parent Company, its subsidiaries, and those entities required to be consolidated under applicable accounting standards. All material intercompany accounts and transactions have been eliminated. Significant Accounting Policies Translation of Foreign Currencies:  The functional currency of Aflac Japan's insurance operations is the Japanese yen. The Company translates its yen-denominated financial statement accounts into U.S. dollars as follows. Assets and liabilities are translated at end-of-period exchange rates. Realized gains and losses on security transactions are translated at the exchange rate on the trade date of each transaction. Other revenues, expenses, and cash flows are translated using average exchange rates for the period. The resulting currency translation adjustments are reported in accumulated other comprehensive income. The Company includes in earnings the realized currency exchange gains and losses resulting from foreign currency transactions. The Parent Company has designated a majority of its yen-denominated liabilities (notes payable and yen-denominated loans) as non-derivative hedges and designated certain foreign currency forwards and options as derivative hedges of the foreign currency exposure of the Company's net investment in Aflac Japan. Outstanding principal and related accrued interest on these Parent Company liabilities and the fair value of these derivatives are translated into U.S. dollars at end-of-period exchange rates. Currency translation adjustments and changes in the fair value of these derivatives are recorded as unrealized foreign currency translation gains (losses) in other comprehensive income and are included in accumulated other comprehensive income. Insurance Revenue and Expense Recognition:  The supplemental health and life insurance policies the Company issues are classified as long-duration contracts. The contract provisions generally cannot be changed or canceled during the contract period; however, the Company may adjust premiums for supplemental health policies issued in the United States within prescribed guidelines and with the approval of state insurance regulatory authorities. Insurance premiums for most of the Company's health and life policies, including cancer, accident, hospital, critical illness, dental, vision, term life, whole life, long-term care and disability, are recognized as revenue over the premium-paying periods of the contracts when due from policyholders. When revenues are reported, the related amounts of benefits and expenses are charged against such revenues, so that profits are recognized in proportion to premium revenues during the period the policies are expected to remain in force. This association is accomplished by means of annual additions to the liability for future policy benefits and the deferral and subsequent amortization of policy acquisition costs. Premiums from the Company's products with limited-pay features, including term life, whole life, WAYS, and child endowment, are collected over a significantly shorter period than the period over which benefits are provided. Premiums for these products are recognized as revenue over the premium-paying periods of the contracts when due from policyholders. Any gross premium in excess of the net premium is deferred and recorded in earnings, such that profits are recognized in a constant relationship with insurance in force. Benefits are recorded as an expense when they are incurred. A liability for future policy benefits is recorded when premiums are recognized using the net premium method. At the policyholder's option, customers can also pay discounted advanced premiums for certain of the Company's products. Advanced premiums are deferred and recognized when due from policyholders over the regularly scheduled premium payment period. The calculation of DAC and the liability for future policy benefits requires the use of estimates based on sound actuarial valuation techniques. For new policy issues, the Company reviews its actuarial assumptions and deferrable acquisition costs each year and revises them when necessary to more closely reflect recent experience and studies of actual acquisition costs. For policies in force, the Company evaluates DAC by major product groupings to determine that they are recoverable from future revenues, and any amounts determined not to be recoverable are charged against net earnings. The Company has not had any material charges to earnings for DAC that was determined not to be recoverable in any of the years presented in this Form 10-K. Advertising expense is reported as incurred in insurance expenses in the consolidated statements of earnings. Cash and Cash Equivalents:  Cash and cash equivalents include cash on hand, money market instruments, and other debt instruments with a maturity of 90 days or less when purchased. Investments:  The Company's debt securities consist of fixed-maturity securities, which are classified as either held to maturity or available for sale. Securities classified as held to maturity are securities that the Company has the ability and intent to hold to maturity or redemption and are carried at amortized cost. All other fixed-maturity debt securities, perpetual securities, and equity securities are classified as available for sale and are carried at fair value. If the fair value is higher than the amortized cost for debt and perpetual securities, or the purchase cost for equity securities, the excess is an unrealized gain, and if lower than cost, the difference is an unrealized loss. The net unrealized gains and losses on securities available for sale, less related deferred income taxes, are recorded through other comprehensive income and included in accumulated other comprehensive income. Amortized cost of debt and perpetual securities is based on the Company's purchase price adjusted for accrual of discount, or amortization of premium, and recognition of impairment charges, if any. The amortized cost of debt and perpetual securities the Company purchases at a discount or premium will equal the face or par value at maturity or the call date, if applicable. Interest is reported as income when earned and is adjusted for amortization of any premium or discount. The Company has investments in variable interest entities (VIEs). Criteria for evaluating VIEs for consolidation focuses on identifying which enterprise has the power to direct the activities of a variable interest entity that most significantly impact the entity's economic performance and (1) the obligation to absorb losses of the entity or (2) the right to receive benefits from the entity. The Company is the primary beneficiary of certain VIEs, and therefore consolidates these entities in its financial statements. While the consolidated VIEs generally operate within a defined set of documents, there are certain powers that are retained by the Company that are considered significant in the conclusion that the Company is the primary beneficiary. These powers vary by structure but generally include the initial selection of the underlying collateral or, for collateralized debt obligations (CDOs), the reference credits to include in the structure; the ability to obtain the underlying collateral in the event of default; and, the ability to appoint or dismiss key parties in the structure. In particular, the Company's powers surrounding the underlying collateral were considered to be the most significant powers since those most significantly impact the economics of the VIE. The Company has no obligation to provide any continuing financial support to any of the entities in which it is the primary beneficiary. The Company's maximum loss is limited to its original investment. Neither the Company nor any of its creditors has the ability to obtain the underlying collateral, nor does the Company have control over the instruments held in the VIEs, unless there is an event of default. For those entities where the Company is the primary beneficiary, the assets consolidated are segregated on the balance sheet by the caption "consolidated variable interest entities," and consist of fixed-maturity securities, perpetual securities, equity securities, loan receivables, and derivative instruments. For the mortgage- and asset-backed securities held in the Company's fixed maturities portfolio, the Company recognizes income using a constant effective yield, which is based on anticipated prepayments and the estimated economic life of the securities. When estimates of prepayments change, the effective yield is recalculated to reflect actual payments to date and anticipated future payments. The net investment in mortgage- and asset-backed securities is adjusted to the amount that would have existed had the new effective yield been applied at the time of acquisition. This adjustment is reflected in net investment income. The Company uses the specific identification method to determine the gain or loss from securities transactions and report the realized gain or loss in the consolidated statements of earnings. Securities transactions are accounted for based on values as of the trade date of the transaction. An investment in a fixed maturity, perpetual security, or equity security is impaired if the fair value falls below book value. The Company regularly reviews its entire investment portfolio for declines in value. The Company's fixed maturities and investment-grade perpetual securities investments are evaluated for other-than-temporary impairment using its debt impairment model. The Company's debt impairment model focuses on the ultimate collection of the cash flows from its investments and whether the Company has the intent to sell or if it is more likely than not the Company would be required to sell the security prior to recovery of its amortized cost. The determination of the amount of impairments under this model is based upon the Company's periodic evaluation and assessment of known and inherent risks associated with the respective securities. Such evaluations and assessments are revised as conditions change and new information becomes available. When determining the Company's intention to sell a security prior to recovery of its fair value to amortized cost, the Company evaluates facts and circumstances such as, but not limited to, future cash flow needs, decisions to reposition its security portfolio, and risk profile of individual investment holdings. The Company performs ongoing analyses of its liquidity needs, which includes cash flow testing of its policy liabilities, debt maturities, projected dividend payments, and other cash flow and liquidity needs. The Company's cash flow testing includes extensive duration analysis of its investment portfolio and policy liabilities. Based on the Company's analyses, the Company has concluded that it has sufficient excess cash flows to meet its liquidity needs without selling any of its investments prior to their maturity. The determination of whether an impairment in value of the Company's fixed maturity securities is other than temporary is based largely on the Company's evaluation of the issuer ' s creditworthiness. The Company must apply considerable judgment in determining the likelihood of its fixed maturity securities recovering in value. Factors that may influence this include the overall level of interest rates, credit spreads, the credit quality of the underlying issuer, and other factors. This process requires consideration of risks which can be controlled to a certain extent, such as credit risk, and risks which cannot be controlled, such as interest rate risk and foreign currency risk. If, after monitoring and analyses, management believes that fair value will not recover to amortized cost prior to the disposal of the security, the Company recognizes an other-than-temporary impairment of the security. Once a security is considered to be other-than-temporarily impaired, the impairment loss is separated into two separate components: the portion of the impairment related to credit and the portion of the impairment related to factors other than credit. The Company recognizes a charge to earnings for the credit-related portion of other-than-temporary impairments. Impairments related to factors other than credit are charged to earnings in the event the Company intends to sell the security prior to the recovery of its amortized cost or if it is more likely than not that the Company would be required to dispose of the security prior to recovery of its amortized cost; otherwise, non-credit-related other-than-temporary impairments are charged to other comprehensive income. The Company's investments in perpetual securities that are rated below investment grade and equity securities are evaluated for other-than-temporary impairment under the Company's equity impairment model. The Company's equity impairment model focuses on the severity of a security's decline in fair value coupled with the length of time the fair value of the security has been below amortized cost and the financial condition and near-term prospects of the issuer. For equity securities that have declines in value that are deemed to be temporary, the Company makes an assertion as to its ability and intent to retain the security until recovery. Once identified, these equity securities are restricted from trading unless authorized based upon significant events that could not have been foreseen at the time the Company asserted its ability and intent to retain the security until recovery. If management believes that the equity security will not recover prior to the disposal of the security, the Company recognizes an other-than-temporary impairment of the security. Once an equity security is considered to be other-than-temporarily impaired, its fair value on that date becomes the new cost basis and the impairment loss is recognized in earnings. The Company lends fixed-maturity securities to financial institutions in short-term security lending transactions. These securities continue to be carried as investment assets on the Company's balance sheet during the terms of the loans and are not reported as sales. The Company receives cash or other securities as collateral for such loans. For loans involving unrestricted cash or securities as collateral, the collateral is reported as an asset with a corresponding liability for the return of the collateral. Other investments include transitional real estate loans (TREs), commercial mortgage loans (CMLs), middle market loans (MMLs), policy loans, limited partnerships, and other short-term investments with maturities of one year or less, but greater than 90 days, at the time of purchase. The Company invests in TREs, CMLs, and MMLs that are accounted for as loan receivables and recorded at amortized cost on the acquisition date. Since the Company has the intent and ability to hold these loan receivables for the foreseeable future or until they mature, they are considered held for investment and are carried at adjusted amortized cost in the other investments line on its consolidated balance sheets. The adjusted amortized cost of the loan receivables reflects allowances for expected incurred losses estimated based on past events and current economic conditions as of each reporting date. Limited partnership investments are accounted for using the equity method of accounting. Under the equity method of accounting, the Company reports its portion of partnership earnings as a component of net investment income in its consolidated statements of earnings. The underlying investments held by the Company’s limited partnerships primarily consist of private equity. Other short-term investments are stated at amortized cost, which approximates estimated fair value. Derivatives and Hedging:  Freestanding derivative instruments are reported in the consolidated balance sheet at fair value and are reported in other assets and other liabilities, with changes in value reported in earnings and/or other comprehensive income. These freestanding derivatives are interest rate swaps, foreign currency swaps, credit default swaps (CDSs), foreign currency forwards, foreign currency options, and, in prior year periods, options on interest rate swaps (or interest rate swaptions). Interest rate and foreign currency swaps are used within VIEs to hedge the risk arising from interest rate and currency exchange risk, while the CDSs are used to increase the yield and improve the diversification of the portfolio. Foreign currency forwards and options are used in hedging foreign exchange risk on U.S. dollar-denominated investments in Aflac Japan's portfolio. Foreign currency forwards and options are used to hedge certain portions of forecasted cash flows denominated in yen. Interest rate swaps are used to hedge the variability of interest cash flows associated with the Company's variable interest rate notes. Cross-currency interest rate swaps, also referred to as foreign currency swaps, are used to economically convert certain U.S. dollar-denominated note obligations into yen-denominated principal and interest obligations. Interest rate swaptions have been used from time to time to hedge interest rate risk for certain U.S. dollar-denominated available-for-sale securities. The Company does not use derivatives for trading purposes, nor does the Company engage in leveraged derivative transactions. From time to time, the Company purchases certain investments that contain an embedded derivative. The Company assesses whether this embedded derivative is clearly and closely related to the asset that serves as its host contract. If the Company deems that the embedded derivative's terms are not clearly and closely related to the host contract, and a separate instrument with the same terms would qualify as a derivative instrument, the derivative is separated from that contract, held at fair value, and reported with the host instrument in the consolidated balance sheet, with changes in fair value reported in earnings. If the Company has elected the fair value option, the embedded derivative is not bifurcated, and the entire investment is held at fair value with changes in fair value reported in earnings. See Note 5 for a discussion on how the Company determines the fair value of its derivatives. Accruals on derivatives are typically recorded in accrued investment income or within other liabilities in the consolidated balance sheets. To qualify for hedge accounting treatment, a derivative must be highly effective in mitigating the designated risk of the hedged item. At the inception of hedging relationships for which the Company elects to designate for hedge accounting treatment, the Company formally documents all relationships between hedging instruments and hedged items, as well as its risk-management objectives and strategies for undertaking each hedge transaction. The Company documents the designation of each hedge as either (i) a hedge of the variability of cash flows to be received or paid related to a recognized asset or liability or the hedge of a forecasted transaction ("cash flow hedge"); (ii) a hedge of the estimated fair value of a recognized asset or liability ("fair value hedge"); or (iii) a hedge of a net investment in a foreign operation. The documentation process includes linking derivatives and non-derivative financial instruments that are designated as hedges to specific assets or groups of assets or liabilities on the statement of financial position or to specific forecasted transactions and defining the effectiveness and ineffectiveness testing methods to be used. At the hedge's inception and on an ongoing quarterly basis, the Company also formally assesses whether the derivatives and non-derivative financial instruments used in hedging activities have been, and are expected to continue to be, highly effective in offsetting their designated risk. Hedge effectiveness is assessed using qualitative and quantitative methods. The assessment of hedge effectiveness determines the accounting treatment of noncash changes in fair value. For assessing hedge effectiveness of cash flow hedges, qualitative methods may include the comparison of critical terms of the derivative to the hedged item, and quantitative methods may include regression or other statistical analysis of changes in cash flows associated with the hedge relationship. Hedge ineffectiveness of the hedge relationships on the Company's VIE cash flow hedges is measured each reporting period using the “Hypothetical Derivative Method.” For derivative instruments that are designated and qualify as cash flow hedges, the effective portion of the gain or loss on the derivative is reported as a component of other comprehensive income (loss) and reclassified into earnings in the same period or periods during which the hedged transaction affects earnings. Gains and losses on the derivative representing hedge ineffectiveness are recognized in current earnings within derivative and other gains (losses). All components of each derivative's gain or loss are included in the assessment of hedge effectiveness. Periodic derivative net coupon settlements are recorded in the line item of the consolidated statements of earnings in which the cash flows of the hedged item are recorded. For assessing hedge effectiveness of fair value hedges, qualitative methods may include the comparison of critical terms of the derivative to the hedged item, and quantitative methods may include regression or other statistical analysis of changes in fair value associated with the hedge relationship. Hedge ineffectiveness of the hedge relationships is measured each reporting period using the dollar offset method. For derivative instruments that are designated and qualify as fair value hedges, changes in the estimated fair value of the derivative, including amounts measured as ineffectiveness, and changes in the estimated fair value of the hedged item related to the designated risk being hedged, are reported in current earnings within derivative and other gains (losses). When assessing the effectiveness of the Company's fair value hedges, the Company excludes the changes in fair value related to the difference between the spot and the forward rate on its foreign currency forwards and the time value of options. For the hedge of the Company's net investment in Aflac Japan, the Company has designated the majority of the Parent Company's yen-denominated liabilities (notes payable and yen-denominated loans) as non-derivative hedging instruments and has designated certain foreign currency forwards and options as derivative hedging instruments. The Company makes its net investment hedge designation at the beginning of each quarter. For assessing hedge effectiveness of net investment hedges, if the total of the designated Parent Company non-derivative and derivatives notional is equal to or less than its net investment in Aflac Japan, the hedge is deemed to be effective. If the hedge is effective, the related exchange effect on the yen-denominated liabilities is reported in the unrealized foreign currency component of other comprehensive income. For derivatives designated as net investment hedges, Aflac follows the forward-rate method. According to that method, all changes in fair value, including changes related to the forward-rate component of foreign currency forward contracts and the time value of foreign currency options, are reported in the unrealized foreign currency component of other comprehensive income. Should these designated net investment hedge positions exceed the Company's net investment in Aflac Japan, the foreign exchange effect on the portion that exceeds its investment in Aflac Japan would be recognized in current earnings within derivative and other gains (losses). The Company discontinues hedge accounting prospectively when (1) it is determined that the derivative is no longer highly effective in offsetting changes in the estimated cash flows or fair value of a hedged item; (2) the derivative is de-designated as a hedging instrument; or (3) the derivative expires or is sold, terminated or exercised. When hedge accounting is discontinued on a cash flow hedge or fair value hedge, the derivative is carried in the consolidated balance sheets at its estimated fair value, with changes in estimated fair value recognized in current period earnings. For discontinued cash flow hedges, including those where the derivative is sold, terminated or exercised, amounts previously deferred in other comprehensive income (loss) are reclassified into earnings when earnings are impacted by the cash flow of the hedged item. If a derivative is not designated as an accounting hedge or its use in managing risk does not qualify for hedge accounting, changes in the estimated fair value of the derivative are generally reported within derivative and other gains (losses), which is a component of realized investment gains (losses). The fluctuations in estimated fair value of derivatives that have not been designated for hedge accounting can result in volatility in net earnings. The Company receives and pledges cash or other securities as collateral on open derivative positions. Cash received as collateral is reported as an asset with a corresponding liability for the return of the collateral. Cash pledged as collateral is recorded as a reduction to cash, and a corresponding receivable is recognized for the return of the cash collateral. The Company generally can repledge or resell collateral obtained from counterparties, although the Company does not typically exercise such rights. Securities received as collateral are not recognized unless the Company was to exercise its right to sell that collateral or exercise remedies on that collateral upon a counterparty default. Securities that the Company has pledged as collateral continue to be carried as investment assets on its balance sheet. Deferred Policy Acquisition Costs: Certain direct and incremental costs of acquiring new business are deferred and amortized with interest over the premium payment periods in proportion to the ratio of annual premium income to total anticipated premium income. Anticipated premium income is estimated by using the same mortality, persistency and interest assumptions used in computing liabilities for future policy benefits. In this manner, the related acquisition expenses are matched with revenues. Deferred costs include the excess of current-year commissions over ultimate renewal-year commissions and certain incremental direct policy issue, underwriting and sales expenses. All of these incremental costs are directly related to successful policy acquisition. For some products, policyholders can elect to modify product benefits, features, rights or coverages by exchanging a contract for a new contract or by amendment, endorsement, or rider to a contract, or by the election of a feature or coverage within a contract. These transactions are known as internal replacements. The Company performs a two-stage analysis of the internal replacements to determine if the modification is substantive to the base policy. The stages of evaluation are as follows: 1) determine if the modification is integrated with the base policy, and 2) if it is integrated, determine if the resulting contract is substantially changed. For internal replacement transactions where the resulting contract is substantially unchanged, the policy is accounted for as a continuation of the replaced contract. Unamortized deferred acquisition costs from the original policy continue to be amortized over the expected life of the new policy, and the costs of replacing the policy are accounted for as policy maintenance costs and expensed as incurred. Examples include conversions of same age bands, certain family coverage changes, pricing era changes (decrease), and ordinary life becomes reduced paid-up and certain reinstatements. An internal replacement transaction that results in a policy that is substantially changed is accounted for as an extinguishment of the original policy and the issuance of a new policy. Unamortized deferred acquisition costs on the original policy are immediately expensed, and the costs of acquiring the new policy are capitalized and amortized in accordance with the Company's accounting policies for deferred acquisition costs. Further, the policy reserves are evaluated based on the new policy features, and any change (up or down) necessary is recognized at the date of contract change/modification. Examples include conversions-higher age bands, certain family coverage changes, pricing era changes (increase), lapse & re-issue, certain reinstatements and certain contract conversions. Riders can be considered internal replacements that are either integrated or non-integrated resulting in either substantially changed or substantially unchanged treatment. Riders are evaluated based on the specific facts and circumstances of the rider and are considered an expansion of the existing benefits with additional premium required. Non-integrated riders to existing contracts do not change the Company's profit expectations for the related products and are treated as a new policy establishment for incremental coverage. The Company measures the recoverability of DAC and the adequacy of its policy reserves annually by performing gross premium valuations on its business. (See the following discussion for further information regarding policy reserves.) Policy Liabilities:  Future policy benefits represent claims that are expected to occur in the future and are computed by a net level premium method using estimated future investment yields, persistency and recognized morbidity and mortality tables modified to reflect the Company's experience, including a provision for adverse deviation. These assumptions are generally established and considered l

BUSINESS SEGMENT AND FOREIGN IN

BUSINESS SEGMENT AND FOREIGN INFORMATION	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
BUSINESS SEGMENT INFORMATION	BUSINESS SEGMENT AND FOREIGN INFORMATION The Company consists of two reportable insurance business segments: Aflac Japan and Aflac U.S., both of which sell supplemental health and life insurance. Operating business segments that are not individually reportable and business activities, including reinsurance retrocession activities, not included in Aflac Japan or Aflac U.S. are included in the "Other business segments" category. The Company does not allocate corporate overhead expenses to business segments. Consistent with U.S. GAAP accounting guidance for segment reporting, the Company evaluates and manages its business segments using a financial performance measure called pretax operating earnings. The Company's definition of operating earnings includes interest cash flows associated with notes payable and amortized hedge costs related to foreign currency denominated investments, but excludes certain items that cannot be predicted or that are outside of the management's control, such as realized investment gains and losses from securities transactions, impairments, change in loan loss reserves and certain derivative and foreign currency activities; nonrecurring items; and other non-operating income (loss) from net earnings. Nonrecurring and other non-operating items consist of infrequent events and activity not associated with the normal course of the Company’s insurance operations and do not reflect Aflac’s underlying business performance. The Company excludes income taxes related to operations to arrive at pretax operating earnings. Information regarding operations by segment for the years ended December 31 follows: (In millions) 2017 2016 2015 Revenues: Aflac Japan: Net earned premiums: Cancer $ 5,612 $ 5,639 $ 4,933 Medical and other health 3,379 3,429 3,092 Life insurance 3,761 4,469 4,021 Net investment income, less amortized hedge costs (1) 2,235 2,368 2,364 Other income 41 40 31 Total Aflac Japan 15,028 15,945 14,441 Aflac U.S.: Net earned premiums: Accident/disability 2,537 2,469 2,391 Cancer 1,308 1,299 1,293 Other health 1,445 1,415 1,395 Life insurance 273 271 268 Net investment income 721 703 678 Other income 5 10 8 Total Aflac U.S. 6,289 6,167 6,033 Other business segments 140 275 225 Total business segment revenues 21,457 22,387 20,699 Corporate and eliminations 210 85 79 Total operating revenues 21,667 22,472 20,778 Realized investment gains (losses) (1), (2), (3) 0 87 94 Total revenues $ 21,667 $ 22,559 $ 20,872 (1) Amortized hedge costs related to hedging U.S. dollar-denominated investments held in Aflac Japan were $228 , $186 and $72 for 2017, 2016 and 2015, respectively, and have been reclassified from realized investment gains (losses) and reported as a deduction from net investment income when analyzing segment operations to conform to current year reporting. (2) Excluding a gain of $77 in 2017 and $85 in both 2016 and 2015 related to the interest rate component of the change in fair value of foreign currency swaps on notes payable which is classified as an operating gain when analyzing segment operations (3) Prior year foreign currency transaction gains and losses have been reclassified from other non-operating income (loss) to realized investment gains (losses) to conform to current-year reporting classifications. These reclassifications had no impact on total revenues. (In millions) 2017 2016 2015 Pretax earnings: Aflac Japan (1) $ 3,054 $ 3,148 $ 3,103 Aflac U.S. 1,245 1,208 1,101 Other business segments 11 18 14 Total business segment pretax operating earnings 4,310 4,374 4,218 Interest expense, noninsurance operations (122 ) (128 ) (146 ) Corporate and eliminations (101 ) (129 ) (71 ) Pretax operating earnings 4,087 4,117 4,001 Realized investment gains (losses) (1), (2), (3) 0 87 94 Other non-operating income (loss) (3), (4) (69 ) (137 ) (233 ) Total earnings before income taxes $ 4,018 $ 4,067 $ 3,862 Income taxes applicable to pretax operating earnings $ 1,370 $ 1,426 $ 1,377 Effect of foreign currency translation on after-tax (41 ) 141 (198 ) (1) Amortized hedge costs related to hedging U.S. dollar-denominated investments held in Aflac Japan were $228 , $186 and $72 for 2017, 2016 and 2015 respectively, and have been reclassified from realized investment gains (losses) and reported as a deduction from pretax operating earnings when analyzing segment operations to conform to current year reporting. (2) Excluding a gain of $77 in 2017 and $85 in both 2016 and 2015 related to the interest rate component of the change in fair value of foreign currency swaps on notes payable which is classified as an operating gain when analyzing segment operations (3) Prior year foreign currency transaction gains and losses have been reclassified from other non-operating income (loss) to realized investment gains (losses) to conform to current-year reporting classifications. These reclassifications had no impact on total earnings before income taxes. (4) Includes expense of $13 in 2017, $137 in 2016 and $230 in 2015 for the early extinguishment of debt Assets as of December 31 were as follows: (In millions) 2017 2016 2015 Assets: Aflac Japan $ 114,402 $ 107,858 $ 97,646 Aflac U.S. 19,893 19,453 18,537 Other business segments 547 270 188 Total business segment assets 134,842 127,581 116,371 Corporate and eliminations 2,375 2,238 1,885 Total assets $ 137,217 $ 129,819 $ 118,256 Amounts prior to 2016 have been adjusted for the adoption of the accounting guidance on January 1, 2016 related to debt issuance costs. Yen-Translation Effects:  The following table shows the yen/dollar exchange rates used for or during the periods ended December 31 . Exchange effects were calculated using the same yen/dollar exchange rate for the current year as for each respective prior year. 2017 2016 2015 Statements of Earnings: Weighted-average yen/dollar exchange rate 112.16 108.70 120.99 Yen percent strengthening (weakening) (3.1 )% 11.3 % (12.8 )% Exchange effect on pretax operating earnings (in millions) $ (63 ) $ 218 $ (288 ) 2017 2016 Balance Sheets: Yen/dollar exchange rate at December 31 113.00 116.49 Yen percent strengthening (weakening) 3.1 % 3.5 % Exchange effect on total assets (in millions) $ 2,593 $ 2,820 Exchange effect on total liabilities (in millions) 2,848 3,109 Transfers of funds from Aflac Japan:  Aflac Japan makes payments to the Parent Company for management fees and to Aflac U.S. for allocated expenses and profit repatriations. Information on transfers for each of the years ended December 31 is shown below. See Note 13 for information concerning restrictions on transfers from Aflac Japan. (In millions) 2017 2016 2015 Management fees $ 93 $ 79 $ 53 Allocated expenses 109 106 101 Profit repatriation 1,150 1,286 2,139 Total transfers from Aflac Japan $ 1,352 $ 1,471 $ 2,293 Property and Equipment:  The costs of buildings, furniture and equipment are depreciated principally on a straight-line basis over their estimated useful lives (maximum of 50 years for buildings and 20 years for furniture and equipment). Expenditures for maintenance and repairs are expensed as incurred; expenditures for betterments are capitalized and depreciated. Classes of property and equipment as of December 31 were as follows: (In millions) 2017 2016 Property and equipment: Land $ 168 $ 166 Buildings 441 421 Equipment and furniture 372 355 Total property and equipment 981 942 Less accumulated depreciation 547 509 Net property and equipment $ 434 $ 433 Receivables:  Receivables consist primarily of monthly insurance premiums due from individual policyholders or their employers for payroll deduction of premiums, net of an allowance for doubtful accounts. At December 31, 2017 , $334 million , or 40.4% of total receivables, were related to Aflac Japan's operations, compared with $207 million , or 30.9% , at December 31, 2016 .

INVESTMENTS

INVESTMENTS	12 Months Ended
	Dec. 31, 2017
Investments [Abstract]
INVESTMENTS	INVESTMENTS Net Investment Income The components of net investment income for the years ended December 31 were as follows: (In millions) 2017 2016 2015 Fixed-maturity securities $ 3,094 $ 3,214 $ 3,094 Perpetual securities 79 94 114 Equity securities 42 35 3 Other investments 94 31 15 Short-term investments and cash equivalents 25 11 4 Gross investment income 3,334 3,385 3,230 Less investment expenses 114 107 95 Net investment income $ 3,220 $ 3,278 $ 3,135 Investment Holdings The amortized cost for the Company's investments in debt and perpetual securities, the cost for equity securities and the fair values of these investments at December 31 are shown in the following tables. 2017 (In millions) Cost or Gross Gross Fair Securities available for sale, carried at fair value: Fixed maturities: Yen-denominated: Japan government and agencies $ 27,980 $ 3,363 $ 271 $ 31,072 Municipalities 314 28 12 330 Mortgage- and asset-backed securities 242 29 0 271 Public utilities 1,635 352 6 1,981 Sovereign and supranational 1,380 190 1 1,569 Banks/financial institutions 3,521 524 26 4,019 Other corporate 3,890 771 7 4,654 Total yen-denominated 38,962 5,257 323 43,896 U.S. dollar-denominated: U.S. government and agencies 146 13 1 158 Municipalities 872 168 0 1,040 Mortgage- and asset-backed securities 161 12 0 173 Public utilities 5,116 884 27 5,973 Sovereign and supranational 267 73 0 340 Banks/financial institutions 2,762 604 8 3,358 Other corporate 25,384 2,620 418 27,586 Total U.S. dollar-denominated 34,708 4,374 454 38,628 Total fixed maturities 73,670 9,631 777 82,524 Perpetual securities: Yen-denominated: Banks/financial institutions 1,221 287 27 1,481 Other corporate 195 38 0 233 U.S. dollar-denominated: Banks/financial institutions 46 29 0 75 Total perpetual securities 1,462 354 27 1,789 Equity securities: Yen-denominated 561 135 1 695 U.S. dollar-denominated 285 45 2 328 Total equity securities 846 180 3 1,023 Total securities available for sale $ 75,978 $ 10,165 $ 807 $ 85,336 2017 (In millions) Cost or Gross Gross Fair Securities held to maturity, carried at amortized cost: Fixed maturities: Yen-denominated: Japan government and agencies $ 21,331 $ 5,160 $ 0 $ 26,491 Municipalities 357 105 0 462 Mortgage- and asset-backed securities 26 1 0 27 Public utilities 3,300 398 0 3,698 Sovereign and supranational 1,523 312 0 1,835 Banks/financial institutions 2,206 190 9 2,387 Other corporate 2,687 485 0 3,172 Total yen-denominated 31,430 6,651 9 38,072 Total securities held to maturity $ 31,430 $ 6,651 $ 9 $ 38,072 2016 (In millions) Cost or Gross Gross Fair Securities available for sale, carried at fair value: Fixed maturities: Yen-denominated: Japan government and agencies $ 22,857 $ 3,359 $ 160 $ 26,056 Municipalities 246 29 8 267 Mortgage- and asset-backed securities 1,096 33 8 1,121 Public utilities 1,533 318 3 1,848 Sovereign and supranational 862 186 5 1,043 Banks/financial institutions 2,673 403 74 3,002 Other corporate 3,192 623 3 3,812 Total yen-denominated 32,459 4,951 261 37,149 U.S dollar-denominated: U.S. government and agencies 148 10 0 158 Municipalities 894 142 8 1,028 Mortgage- and asset-backed securities 196 20 0 216 Public utilities 5,205 690 60 5,835 Sovereign and supranational 335 91 0 426 Banks/financial institutions 2,570 507 16 3,061 Other corporate 24,556 2,021 690 25,887 Total U.S. dollar-denominated 33,904 3,481 774 36,611 Total fixed maturities 66,363 8,432 1,035 73,760 Perpetual securities: Yen-denominated: Banks/financial institutions 1,266 128 49 1,345 Other corporate 189 24 0 213 U.S. dollar-denominated: Banks/financial institutions 51 24 0 75 Total perpetual securities 1,506 176 49 1,633 Equity securities: Yen-denominated 624 83 2 705 Dollar-denominated 579 31 6 604 Total equity securities 1,203 114 8 1,309 Total securities available for sale $ 69,072 $ 8,722 $ 1,092 $ 76,702 2016 (In millions) Cost or Gross Gross Fair Securities held to maturity, carried at amortized cost: Fixed maturities: Yen-denominated: Japan government and agencies $ 20,702 $ 5,338 $ 0 $ 26,040 Municipalities 350 107 0 457 Mortgage- and asset-backed securities 30 2 0 32 Public utilities 3,201 358 23 3,536 Sovereign and supranational 2,602 283 8 2,877 Banks/financial institutions 3,731 195 26 3,900 Other corporate 2,734 452 7 3,179 Total yen-denominated 33,350 6,735 64 40,021 Total securities held to maturity $ 33,350 $ 6,735 $ 64 $ 40,021 The methods of determining the fair values of the Company's investments in fixed-maturity securities, perpetual securities and equity securities are described in Note 5. During 2017, the Company reclassified three investments from the held-to-maturity category to the available-for-sale category as a result of the issuers' credit rating being downgraded to below investment grade. At the time of the transfer, the securities had an aggregate amortized cost of $773 million and an aggregate unrealized gain of $47 million . During 2016 and 2015, the Company did not reclassify any investments from the held-to-maturity category to the available-for-sale category. Contractual and Economic Maturities The contractual maturities of the Company's investments in fixed maturities at December 31, 2017 , were as follows: Aflac Japan Aflac U.S. (In millions) Amortized Fair Amortized Fair Available for sale: Due in one year or less $ 234 $ 243 $ 86 $ 89 Due after one year through five years 7,155 7,391 508 542 Due after five years through 10 years 7,812 8,385 2,726 2,946 Due after 10 years 45,028 51,269 8,482 9,927 Mortgage- and asset-backed securities 283 322 40 41 Total fixed maturities available for sale $ 60,512 $ 67,610 $ 11,842 $ 13,545 Held to maturity: Due in one year or less $ 885 $ 903 $ 0 $ 0 Due after one year through five years 434 455 0 0 Due after five years through 10 years 1,634 1,802 0 0 Due after 10 years 28,451 34,885 0 0 Mortgage- and asset-backed securities 26 27 0 0 Total fixed maturities held to maturity $ 31,430 $ 38,072 $ 0 $ 0 At December 31, 2017 , the Parent Company and other business segments had portfolios of available-for-sale fixed-maturity securities totaling $1.3 billion at amortized cost and $1.4 billion at fair value, which are not included in the table above. Expected maturities may differ from contractual maturities because some issuers have the right to call or prepay obligations with or without call or prepayment penalties. The majority of the Company's perpetual securities are subordinated to other debt obligations of the issuer, but rank higher than the issuer's equity securities. Perpetual securities have characteristics of both debt and equity investments, along with unique features that create economic maturity dates for the securities. Although perpetual securities have no contractual maturity date, they have stated interest coupons that were fixed at their issuance and subsequently change to a floating short-term interest rate after some period of time. The instruments are generally callable by the issuer at the time of changing from a fixed coupon rate to a new variable rate of interest, which is determined by the combination of some market index plus a fixed amount of basis points. The net effect is to create an expected maturity date for the instrument. The economic maturities of the Company's investments in perpetual securities, which were all reported as available for sale at December 31, 2017 , were as follows: Aflac Japan Aflac U.S. (In millions) Amortized Fair Amortized Fair Due after one year through five years $ 194 $ 233 $ 0 $ 0 Due after 10 years 1,229 1,495 39 61 Total perpetual securities available for sale $ 1,423 $ 1,728 $ 39 $ 61 Investment Concentrations The Company's process for investing in credit-related investments begins with an independent approach to underwriting each issuer's fundamental credit quality. The Company evaluates independently those factors that it believes could influence an issuer's ability to make payments under the contractual terms of the Company's instruments. This includes a thorough analysis of a variety of items including the issuer's country of domicile (including political, legal, and financial considerations); the industry in which the issuer competes (with an analysis of industry structure, end-market dynamics, and regulation); company specific issues (such as management, assets, earnings, cash generation, and capital needs); and contractual provisions of the instrument (such as financial covenants and position in the capital structure). The Company further evaluates the investment considering broad business and portfolio management objectives, including asset/liability needs, portfolio diversification, and expected income. Investment exposures that individually exceeded 10% of shareholders' equity as of December 31 were as follows: 2017 2016 (In millions) Credit Amortized Fair Credit Amortized Fair Japan National Government (1) A $48,399 $56,532 A $42,931 $51,345 (1) Japan Government Bonds (JGBs) or JGB-backed securities Realized Investment Gains and Losses Information regarding pretax realized gains and losses from investments for the years ended December 31 follows: (In millions) 2017 2016 2015 Realized investment gains (losses): Fixed maturities: Available for sale: Gross gains from sales $ 36 $ 77 $ 224 Gross losses from sales (82 ) (134 ) (8 ) Net gains (losses) from redemptions (23 ) 112 51 Other-than-temporary impairment losses (7 ) (24 ) (152 ) Total fixed maturities (76 ) 31 115 Perpetual securities: Available for sale: Net gains (losses) from redemptions 4 64 35 Other-than-temporary impairment losses 0 (2 ) 0 Total perpetual securities 4 62 35 Equity securities: Gross gains from sales 104 0 0 Gross losses from sales (11 ) 0 0 Net gains (losses) from redemptions 0 22 0 Other-than-temporary impairment losses (22 ) (57 ) (1 ) Total equity securities 71 (35 ) (1 ) Loan loss reserves (8 ) (2 ) (1 ) Derivatives and other: Derivative gains (losses) (109 ) (255 ) (10 ) Foreign currency gains (losses) (33 ) 185 (32 ) Total derivatives and other (142 ) (70 ) (42 ) Total realized investment gains (losses) $ (151 ) $ (14 ) $ 106 Prior year foreign currency transaction gains and losses have been reclassified to conform to current-year reporting classifications Unrealized Investment Gains and Losses Information regarding changes in unrealized gains and losses from investments for the years ended December 31 follows: (In millions) 2017 2016 2015 Changes in unrealized gains (losses): Fixed maturities: Available for sale $ 1,457 $ 2,690 $ (2,481 ) Perpetual securities: Available for sale 200 21 (123 ) Equity securities 71 88 9 Total change in unrealized gains (losses) $ 1,728 $ 2,799 $ (2,595 ) Effect on Shareholders' Equity The net effect on shareholders' equity of unrealized gains and losses from investment securities at December 31 was as follows: (In millions) 2017 2016 Unrealized gains (losses) on securities available for sale $ 9,358 $ 7,630 Deferred income taxes (1) (3,394 ) (2,825 ) Shareholders’ equity, unrealized gains (losses) on investment securities $ 5,964 $ 4,805 (1) See Note 10 for discussion of the accounting treatment of tax on amounts recorded in accumulated other comprehensive income pursuant to the Tax Act. Gross Unrealized Loss Aging The following tables show the fair values and gross unrealized losses of the Company's available-for-sale and held-to-maturity investments that were in an unrealized loss position, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position at December 31 . 2017 Total Less than 12 months 12 months or longer (In millions) Fair Unrealized Fair Unrealized Fair Unrealized Fixed Maturities: U.S. government and U.S. dollar-denominated $ 74 $ 1 $ 74 $ 1 $ 0 $ 0 Japan government and Yen-denominated 5,255 271 1,264 9 3,991 262 Municipalities: Yen-denominated 129 12 10 0 119 12 Public utilities: U.S. dollar-denominated 785 27 221 3 564 24 Yen-denominated 83 6 0 0 83 6 Sovereign and supranational: Yen-denominated 309 1 309 1 0 0 Banks/financial institutions: U.S. dollar-denominated 362 8 316 5 46 3 Yen-denominated 1,162 35 394 4 768 31 Other corporate: U.S. dollar-denominated 7,741 418 2,839 50 4,902 368 Yen-denominated 440 7 349 4 91 3 Total fixed maturities 16,340 786 5,776 77 10,564 709 Perpetual securities: Yen-denominated 345 27 0 0 345 27 Total perpetual securities 345 27 0 0 345 27 Equity securities: U.S. dollar-denominated 41 2 21 0 20 2 Yen-denominated 40 1 39 1 1 0 Total equity securities 81 3 60 1 21 2 Total $ 16,766 $ 816 $ 5,836 $ 78 $ 10,930 $ 738 2016 Total Less than 12 months 12 months or longer (In millions) Fair Unrealized Fair Unrealized Fair Unrealized Fixed Maturities: Japan government and Yen-denominated $ 3,958 $ 160 $ 3,958 $ 160 $ 0 $ 0 Municipalities: U.S. dollar-denominated 44 8 0 0 44 8 Yen-denominated 105 8 105 8 0 0 Mortgage- and asset- Yen-denominated 713 8 713 8 0 0 Public utilities: U.S. dollar-denominated 1,265 60 790 32 475 28 Yen-denominated 635 26 347 14 288 12 Sovereign and supranational: Yen-denominated 244 13 38 5 206 8 Banks/financial institutions: U.S. dollar-denominated 268 16 238 10 30 6 Yen-denominated 1,521 100 636 19 885 81 Other corporate: U.S. dollar-denominated 10,462 690 7,252 346 3,210 344 Yen-denominated 321 10 321 10 0 0 Total fixed maturities 19,536 1,099 14,398 612 5,138 487 Perpetual securities: Yen-denominated 479 49 85 1 394 48 Total perpetual securities 479 49 85 1 394 48 Equity securities: U.S. dollar-denominated 211 6 211 6 0 0 Yen-denominated 49 2 49 2 0 0 Total equity securities 260 8 260 8 0 0 Total $ 20,275 $ 1,156 $ 14,743 $ 621 $ 5,532 $ 535 Analysis of Securities in Unrealized Loss Positions The unrealized losses on the Company's fixed maturity or perpetual securities investments have been primarily related to general market changes in interest rates, foreign exchange rates, and/or the levels of credit spreads rather than specific concerns with the issuer's ability to pay interest and repay principal. The unrealized losses on the Company's investments in equity securities are primarily related to foreign exchange rates, general market conditions which reflect prospects for the economy as a whole, or specific information pertaining to an industry or an individual company. For any significant declines in fair value of its fixed income or perpetual securities, the Company performs a more focused review of the related issuers' credit profile. For corporate issuers, the Company evaluates their assets, business profile including industry dynamics and competitive positioning, financial statements and other available financial data. For non-corporate issuers, the Company analyzes all sources of credit support, including issuer-specific factors. The Company utilizes information available in the public domain and, for certain private placement issuers, from consultations with the issuers directly. The Company also considers ratings from Nationally Recognized Statistical Rating Organizations (NRSROs), as well as the specific characteristics of the security it owns including seniority in the issuer's capital structure, covenant predictions, or other relevant features. From these reviews, the Company evaluates the issuers' continued ability to service the Company's investment through payment of interest and principal. For any significant declines in fair value of its equity securities, the Company reviews the severity of the security’s decline in fair value coupled with the length of time the fair value of the security has been below cost. The Company also performs a more focused review of the financial condition and near-term prospects of the issuer as well as general market conditions reflecting the prospects for the economy as a whole, and determines whether it has the intent to hold the securities until they recover in value. Assuming no credit-related factors develop, unrealized gains and losses on fixed maturities and perpetual securities are expected to diminish as investments near maturity. Based on its credit analysis, the Company believes that the issuers of its fixed maturity and perpetual security investments in the sectors shown in the table above have the ability to service their obligations to the Company. Other Investments The table below reflects the composition of the carrying value for other investments as of December 31. (In millions) 2017 2016 Other investments: Transitional real estate loans $ 1,235 $ 0 Commercial mortgage loans 908 855 Middle market loans 859 319 Policy loans 210 184 Short-term investments 57 89 Other 133 3 Total other investments $ 3,402 $ 1,450 Loans and Loan Receivables The Company classifies its TREs, CMLs, and MMLs as held-for investment and includes them in the other investments line on the consolidated balance sheets. The Company carries them on the balance sheet at amortized cost less an estimated allowance for loan losses. The Company's allowance for loan losses is established using both general and specific allowances. The general allowance is used for loans grouped by similar risk characteristics where a loan-specific or market-specific risk has not been identified, but for which the Company estimates probable incurred losses. The specific allowance is used on an individual loan basis when it is probable that a loss has been incurred. As of December 31, 2017 and 2016, the Company's allowance for loan losses was $11 million and $3 million , respectively. As of December 31, 2017 and 2016, the Company had no loans that were past due in regards to principal and/or interest payments. Additionally, the Company held no loans that were on nonaccrual status or considered impaired as of December 31, 2017 and 2016. The Company had no troubled debt restructurings during the years ended December 31, 2017 and 2016. Transitional Real Estate Loans Transitional real estate loans are commercial mortgage loans that are typically relatively short-term floating rate instruments secured by a first lien on the property. These loans provide funding for properties undergoing a change in their physical characteristics and/or economic profile. As of December 31, 2017, the Company had $254 million in outstanding commitments to fund transitional real estate loans, inclusive of loans held in unit trust structures. These commitments are contingent on the final underwriting and due diligence to be performed. Commercial Mortgage Loans As of December 31, 2017, the Company had $13 million in outstanding commitments to fund commercial mortgage loans, inclusive of loans held in unit trust structures. These commitments are contingent on the final underwriting and due diligence to be performed. Middle Market Loans Middle market loans are generally considered to be below investment grade. The carrying value for middle market loans included an unfunded amount of $109 million and $91 million , as of December 31, 2017 and 2016, respectively, that is reflected in other liabilities on the consolidated balance sheets. As of December 31, 2017, the Company had commitments of approximately $552 million to fund potential future loan originations related to this investment program, inclusive of loans held in unit trust structures. These commitments are contingent upon the availability of middle market loans that meet the Company's underwriting criteria. Other Other investments primarily includes investments in limited partnerships. As of December 31, 2017, the Company had $888 million in outstanding commitments to fund alternative investments in limited partnerships. Variable Interest Entities (VIEs) As a condition of its involvement or investment in a VIE, the Company enters into certain protective rights and covenants that preclude changes in the structure of the VIE that would alter the creditworthiness of the Company's investment or its beneficial interest in the VIE. For those VIEs other than certain unit trust structures, the Company's involvement is passive in nature. The Company has not, nor has it been, required to purchase any securities issued in the future by these VIEs. The Company's ownership interest in VIEs is limited to holding the obligations issued by them. The Company has no direct or contingent obligations to fund the limited activities of these VIEs, nor does it have any direct or indirect financial guarantees related to the limited activities of these VIEs. The Company has not provided any assistance or any other type of financing support to any of the VIEs it invests in, nor does it have any intention to do so in the future. For those VIEs in which the Company holds debt obligations, the weighted-average lives of the Company's notes are very similar to the underlying collateral held by these VIEs where applicable. The Company also utilizes unit trust structures in its Aflac Japan segment to invest in various asset classes. As the sole investor of these VIEs, the Company is required to consolidate these entities under U.S. GAAP. The Company's risk of loss related to its interests in any of its VIEs is limited to the carrying value of the related investments held in the VIE. VIEs - Consolidated The following table presents the cost or amortized cost, fair value and balance sheet caption in which the assets and liabilities of consolidated VIEs are reported as of December 31. Investments in Consolidated Variable Interest Entities 2017 2016 (In millions) Cost or Amortized Fair Cost or Amortized Fair Assets: Fixed maturities, available for sale $ 4,300 $ 5,294 $ 4,168 $ 4,982 Perpetual securities, available for sale 238 215 237 208 Equity securities 606 753 972 1,044 Other investments (1) 2,341 2,328 819 789 Other assets (2) 151 151 127 127 Total assets of consolidated VIEs $ 7,636 $ 8,741 $ 6,323 $ 7,150 Liabilities: Other liabilities (2) $ 128 $ 128 $ 146 $ 146 Total liabilities of consolidated VIEs $ 128 $ 128 $ 146 $ 146 (1) Consists of TREs, CMLs, MMLs, and alternative investments in limited partnerships (2) Consists entirely of derivatives The Company is substantively the only investor in the consolidated VIEs listed in the table above. As the sole investor in these VIEs, the Company has the power to direct the activities of a variable interest entity that most significantly impact the entity's economic performance and is therefore considered to be the primary beneficiary of the VIEs that it consolidates. The Company also participates in substantially all of the variability created by these VIEs. The activities of these VIEs are limited to holding invested assets and foreign currency, and/or CDS, as appropriate, and utilizing the cash flows from these securities to service its investment. Neither the Company nor any of its creditors are able to obtain the underlying collateral of the VIEs unless there is an event of default or other specified event. For those VIEs that contain a swap, the Company is not a direct counterparty to the swap contracts and has no control over them. The Company's loss exposure to these VIEs is limited to its original investment. The Company's consolidated VIEs do not rely on outside or ongoing sources of funding to support their activities beyond the underlying collateral and swap contracts, if applicable. With the exception of its investments in unit trust structures, the underlying collateral assets and funding of the Company's consolidated VIEs are generally static in nature and the underlying collateral and the reference corporate entities covered by any CDS contracts were all investment grade at the time of issuance. Investments in Unit Trust Structures The Company invests through unit trust structures in yen-denominated public equity securities, U.S. dollar-denominated public equity securities, bank loans, transitional real estate loans, commercial mortgage loans, middle market loans, infrastructure debt, and alternative investments in limited partnerships. The Company is the only investor in these trusts and meets the requirements to consolidate these trusts under U.S. GAAP. The yen-denominated and U.S. dollar-denominated equity securities, bank loans and certain infrastructure debt are classified as available for sale in the financial statements. The commercial mortgage loans, middle market loans and certain infrastructure debt that meets the criteria to be classified as a loan are classified as loans held for investment and reflected in other investments on the consolidated balance sheets at amortized cost. Limited partnership investments are recognized as equity method investments. VIEs - Not Consolidated The table below reflects the amortized cost, fair value and balance sheet caption in which the Company's investment in VIEs not consolidated are reported as of December 31. Investments in Variable Interest Entities Not Consolidated 2017 2016 (In millions) Amortized Fair Amortized Fair Assets: Fixed maturities, available for sale $ 4,827 $ 5,506 $ 4,729 $ 5,261 Perpetual securities, available for sale 177 218 172 200 Fixed maturities, held to maturity 2,549 2,929 2,563 2,948 Other investments 55 55 1 1 Total investments in VIEs not consolidated $ 7,608 $ 8,708 $ 7,465 $ 8,410 The Company holds alternative investments in limited partnerships that have been determined to be VIEs. These partnerships invest in private equity and structured investments. The Company’s maximum exposure to loss on these investments is limited to the amount of its investment. The Company is not the primary beneficiary of these VIEs and is therefore not required to consolidate them. The Company classifies these investments as Other investments in the consolidated balance sheets. Certain investments in VIEs that the Company is not required to consolidate are investments that are in the form of debt obligations from the VIEs that are irrevocably and unconditionally guaranteed by their corporate parents or sponsors. These VIEs are the primary financing vehicles used by their corporate sponsors to raise financing in the capital markets. The variable interests created by these VIEs are principally or solely a result of the debt instruments issued by them. The Company does not have the power to direct the activities that most significantly impact the entity's economic performance, nor does it have the obligation to absorb losses of the entity or the right to receive benefits from the entity. As such, the Company is not the primary beneficiary of these VIEs and is therefore not required to consolidate them. Securities Lending and Pledged Securities The Company lends fixed-maturity and public equity securities to financial institutions in short-term security-lending transactions. These short-term security-lending arrangements increase investment income with minimal risk. The Company's security lending policy requires that the fair value of the securities and/or unrestricted cash received as collateral be 102% or more of the fair value of the loaned securities. These securities continue to be carried as investment assets on the Company's balance sheet during the terms of the loans and are not reported as sales. The Company receives cash or other securities as collateral for such loans. For loans involving unrestricted cash or securities as collateral, the collateral is reported as an asset with a corresponding liability for the return of the collateral. Details of our securities lending activities as of December 31 were as follows: Securities Lending Transactions Accounted for as Secured Borrowings 2017 Remaining Contractual Maturity of the Agreements (In millions) Overnight (1) Up to 30 Total Securities lending transactions: Japan government and agencies $ 0 $ 49 $ 49 Public utilities 73 0 73 Banks/financial institutions 54 0 54 Other corporate 415 0 415 Equity securities 15 0 15 Total borrowings $ 557 $ 49 $ 606 Gross amount of recognized liabilities for securities lending transactions $ 606 Amounts related to agreements not included in offsetting disclosure in Note 4 $ 0 (1) These securities are pledged as collateral under the Company's U.S. securities lending program and can be called at its discretion; therefore, they are classified as Overnight and Continuous. Securities Lending Transactions Accounted for as Secured Borrowings 2016 Remaining Contractual Maturity of the Agreements (In millions) Overnight (1) Up to 30 Total Securities lending transactions: Public utilities $ 62 $ 0 $ 62 Banks/financial institutions 34 0 34 Other corporate 430 0 430 Total borrowings $ 526 $ 0 $ 526 Gross amount of recognized liabilities for securities lending transactions $ 526 Amounts related to agreements not included in offsetting disclosure in Note 4 $ 0 (1) These securities are pledged as collateral under the Company's U.S. securities lending program and can be called at its discretion; therefore, they are classified as Overnight and Continuous. The Company did not have any repurchase agreements or repurchase-to-maturity transactions outstanding as of December 31, 2017 and 2016, respectively. Certain fixed-maturity securities can be pledged as collateral as part of derivative transactions, or pledged to support state deposit requirements on certain investment programs. For additional information regarding pledged securities related to derivative transactions, see Note 4. At December 31, 2017 , debt securities with a fair value of $21 million were on deposit with regulatory authorities in the United States (including U.S. territories) and Japan. The Company retains ownership of all securities on deposit and receives the related investment income. For general information regarding the Company's investment accounting policies, see Note 1.

DERIVATIVE INSTRUMENTS

DERIVATIVE INSTRUMENTS	12 Months Ended
	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
DERIVATIVE INSTRUMENTS	DERIVATIVE INSTRUMENTS The Company's freestanding derivative financial instruments have historically consisted of: (1) foreign currency forwards and options used in hedging foreign exchange risk on U.S. dollar-denominated investments in Aflac Japan's portfolio; (2) foreign currency forwards and options used to hedge foreign exchange risk from the Company's net investment in Aflac Japan and economically hedge certain portions of forecasted cash flows denominated in yen; (3) swaps associated with the Company's notes payable, consisting of cross-currency interest rate swaps, also referred to as foreign currency swaps, associated with certain senior notes and its subordinated debentures; (4) foreign currency swaps and credit default swaps that are associated with investments in special-purpose entities, including VIEs where the Company is the primary beneficiary; and (5) options on interest rate swaps (or interest rate swaptions) and futures used to hedge interest rate risk for certain available-for-sale securities. The Company does not use derivative financial instruments for trading purposes, nor does it engage in leveraged derivative transactions. Some of the Company's derivatives are designated as cash flow hedges, fair value hedges or net investment hedges; however, other derivatives do not qualify for hedge accounting or the Company elects not to designate them as an accounting hedge. The Company utilizes a net investment hedge to mitigate foreign exchange exposure resulting from its net investment in Aflac Japan. In addition to designating derivatives as hedging instruments, the Company has designated the majority of the Parent Company's yen-denominated liabilities (notes payable and loans) as nonderivative hedging instruments for this net investment hedge. Derivative Types Foreign currency forwards and options are executed for the Aflac Japan segment in order to hedge the currency risk on the carrying value of certain U.S. dollar-denominated investments. The average maturity of these forwards and options can change depending on factors such as market conditions and types of investments being held. In situations where the maturity of the forwards and options are shorter than the underlying investment being hedged, the Company may enter into new forwards and options near maturity of the existing derivative in order to continue hedging the underlying investment. In forward transactions, Aflac Japan agrees with another party to buy a fixed amount of yen and sell a corresponding amount of U.S. dollars at a specified future date. Aflac Japan also executes foreign currency option transactions in a collar strategy, where Aflac Japan agrees with another party to simultaneously purchase a fixed amount of U.S. dollar put options and sell U.S. dollar call options. The combination of these two actions results in no net premium being paid (i.e. a costless or zero-cost collar). The foreign currency forwards and options are used in fair value hedging relationships to mitigate the foreign exchange risk associated with U.S. dollar-denominated investments supporting yen- denominated liabilities. Foreign currency forwards and options are also used to hedge the currency risk associated with the net investment in Aflac Japan. In these forward transactions, Aflac agrees with another party to buy a fixed amount of U.S. dollars and sell a corresponding amount of yen at a specified future date. In the option transactions, the Company uses a combination of foreign currency options to protect expected future cash flows by simultaneously purchasing yen put options (options that protect against a weakening yen) and selling yen call options (options that limit participation in a strengthening yen). The combination of these two actions results in no net premium being paid (i.e. a costless or zero-cost collar). The Company enters into foreign currency swaps pursuant to which it exchanges an initial principal amount in one currency for an initial principal amount of another currency, with an agreement to re-exchange the currencies at a future date at an agreed upon exchange rate. There may also be periodic exchanges of payments at specified intervals based on the agreed upon rates and notional amounts. Foreign currency swaps are used primarily in the consolidated VIEs in the Company's Aflac Japan portfolio to convert foreign-denominated cash flows to yen, the functional currency of Aflac Japan, in order to minimize cash flow fluctuations. The Company also uses foreign currency swaps to economically convert certain of its U.S. dollar-denominated senior note and subordinated debenture principal and interest obligations into yen-denominated obligations. The only CDS that the Company currently hold relates to components of an investment in a VIE and is used to assume credit risk related to an individual security. This CDS contract entitles the consolidated VIE to receive periodic fees in exchange for an obligation to compensate the derivative counterparties should the referenced security issuer experience a credit event, as defined in the contract. Interest rate swaps involve the periodic exchange of cash flows with other parties, at specified intervals, calculated using agreed upon rates or other financial variables and notional principal amounts. Typically, at the time a swap is entered into, the cash flow streams exchanged by the counterparties are equal in value. No cash or principal payments are exchanged at the inception of the contract. Interest rate swaps are primarily used to convert interest receipts on floating-rate fixed-maturity securities contracts to fixed rates. These derivatives are predominantly used to better match cash receipts from assets with cash disbursements required to fund liabilities. Interest rate swaptions are options on interest rate swaps. Interest rate collars are combinations of two swaption positions and are executed in order to hedge certain U.S. dollar-denominated available-for-sale securities that are held in the Aflac Japan segment. The Company uses collars to protect against significant changes in the fair value associated with its U.S. dollar-denominated available-for-sale securities due to interest rates. In order to maximize the efficiency of the collars while minimizing cost, the Company sets the strike price on each collar so that the premium paid for the ‘payer leg’ is offset by the premium received for having sold the ‘receiver leg.’ Periodically, the Company may enter into other derivative transactions depending on general economic conditions. Derivative Balance Sheet Classification The tables below summarize the balance sheet classification of the Company's derivative fair value amounts, as well as the gross asset and liability fair value amounts, at December 31. The fair value amounts presented do not include income accruals. The notional amount of derivative contracts represents the basis upon which pay or receive amounts are calculated and are not reflective of exposure or credit risk. 2017 2016 (In millions) Asset Liability Asset Liability Hedge Designation/ Derivative Notional Fair Value Fair Value Notional Fair Value Fair Value Cash flow hedges: Foreign currency swaps $ 75 $ 0 $ (8 ) $ 75 $ 0 $ (10 ) Total cash flow hedges 75 0 (8 ) 75 0 (10 ) Fair value hedges: Foreign currency forwards 7,640 2 (221 ) 10,965 0 (759 ) Foreign currency options 7,670 0 (2 ) 4,224 2 (32 ) Total fair value hedges 15,310 2 (223 ) 15,189 2 (791 ) Net investment hedge: Foreign currency forwards 5 0 0 209 5 (2 ) Foreign currency options 434 12 (1 ) 843 41 (17 ) Total net investment hedge 439 12 (1 ) 1,052 46 (19 ) Non-qualifying strategies: Foreign currency swaps 5,386 296 (189 ) 6,266 490 (220 ) Foreign currency forwards 3,683 20 (53 ) 21,218 667 (956 ) Foreign currency options 770 0 0 41 0 (2 ) Credit default swaps 88 1 0 86 2 0 Total non-qualifying strategies 9,927 317 (242 ) 27,611 1,159 (1,178 ) Total derivatives $ 25,751 $ 331 $ (474 ) $ 43,927 $ 1,207 $ (1,998 ) Balance Sheet Location Other assets $ 10,948 $ 331 $ 0 $ 18,329 $ 1,207 $ 0 Other liabilities 14,803 0 (474 ) 25,598 0 (1,998 ) Total derivatives $ 25,751 $ 331 $ (474 ) $ 43,927 $ 1,207 $ (1,998 ) Cash Flow Hedges Certain of the Company's consolidated VIEs have foreign currency swaps that qualify for hedge accounting treatment. For those that have qualified, the Company has designated the derivative as a hedge of the variability in cash flows of a forecasted transaction or of amounts to be received or paid related to a recognized asset (“cash flow” hedge). The maximum length of time for which these cash flows are hedged is nine years. The remaining derivatives in the Company's consolidated VIEs that have not qualified for hedge accounting are included in "non-qualifying strategies." Fair Value Hedges The Company designates and accounts for certain foreign currency forwards and options as fair value hedges when they meet the requirements for hedge accounting. These foreign currency forwards and options hedge the foreign currency exposure of certain U.S. dollar-denominated investments. The Company recognizes gains and losses on these derivatives and the related hedged items in current earnings within derivative and other gains (losses). The change in the fair value of the foreign currency forwards related to the changes in the difference between the spot rate and the forward price is excluded from the assessment of hedge effectiveness. The change in fair value of the foreign currency option related to the time value of the option is excluded from the assessment of hedge effectiveness. The Company designates and accounts for interest rate swaptions as fair value hedges when they meet the requirements for hedge accounting. These interest rate swaptions hedge the interest rate exposure of certain U.S. dollar-denominated fixed maturity securities within the investment portfolio of the Company's Aflac Japan segment. The Company recognizes gains and losses on these derivatives and the related hedged items in current earnings within derivative and other gains (losses). The change in the fair value of the interest rate swaptions related to the time value of the option is excluded from the assessment of hedge effectiveness. The following table presents the gains and losses on derivatives and the related hedged items in fair value hedges for the years ended December 31. Fair Value Hedging Relationships (In millions) Hedging Derivatives Hedged Items Hedging Derivatives Hedged Items Total Gains (Losses) Gains (Losses) Gains (Losses) Ineffectiveness 2017: Foreign currency Fixed-maturity and equity securities $ 98 $ (202 ) $ 300 $ (278 ) $ 22 Foreign currency Fixed-maturity securities 21 10 11 (10 ) 1 2016: Foreign currency forwards Fixed-maturity and equity securities $ 207 $ (338 ) $ 545 $ (566 ) $ (21 ) Foreign currency options Fixed-maturity securities (95 ) (18 ) (77 ) 70 (7 ) 2015: Foreign currency forwards Fixed-maturity securities $ (133 ) $ (136 ) $ 3 $ (5 ) $ (2 ) Foreign currency options Fixed-maturity securities (4 ) 3 (7 ) 7 0 Interest rate Fixed-maturity securities (95 ) 19 (114 ) 99 (15 ) Net Investment Hedge The Company's investment in Aflac Japan is affected by changes in the yen/dollar exchange rate. To mitigate this exposure, the Parent Company's yen-denominated liabilities (see Note 9) have been designated as non-derivative hedges and foreign currency forwards and options have been designated as derivative hedges of the foreign currency exposure of the Company's net investment in Aflac Japan. The Company used foreign exchange forwards and options to hedge foreign exchange risk on 90.9 billion yen of profit repatriation received from Aflac Japan in 2017. As of December 31, 2017 , the Company had entered into foreign exchange forwards and options as part of a hedge on 49.5 billion yen of future profit repatriation. The Company's net investment hedge was effective for the years ended December 31, 2017 , 2016 and 2015 . Non-qualifying Strategies For the Company's derivative instruments in consolidated VIEs that do not qualify for hedge accounting treatment, all changes in their fair value are reported in current period earnings within derivative and other gains (losses). The amount of gain or loss recognized in earnings for the Company's VIEs is attributable to the derivatives in those investment structures. While the change in value of the swaps is recorded through current period earnings, the change in value of the available-for-sale fixed-maturity or perpetual securities associated with these swaps is recorded through other comprehensive income. As of December 31, 2017, the Parent Company had cross-currency interest rate swap agreements related to its $550 million senior notes due March 2020, $350 million senior notes due February 2022, $700 million senior notes due June 2023, $750 million senior notes due November 2024 and $450 million senior notes due March 2025. Changes in the values of these swaps are recorded through current period earnings. For additional information regarding these swaps, see Note 9. The Company uses foreign exchange forwards and options to mitigate the currency risk of some of its U.S. dollar-denominated loan receivables held within the Aflac Japan segment. The Company has not elected to apply hedge accounting for these loan receivables due to the the change in fair value of the foreign exchange forwards and the foreign currency remeasurement of the loan receivables being recorded through current period earnings, and generally offsetting each other within realized investment gains (losses). Impact of Derivatives and Hedging Instruments The following table summarizes the impact to realized investment gains (losses) and other comprehensive income (loss) from all derivatives and hedging instruments for the years ended December 31. 2017 2016 2015 (In millions) Realized Investment Other (1) Realized Investment Other (1) Realized Other (1) Qualifying hedges: Cash flow hedges: Foreign currency swaps $ 0 $ 1 $ 1 $ 3 $ 0 $ 0 Total cash flow hedges 0 1 1 3 0 0 Fair value hedges: Foreign currency forwards (2) (180 ) 0 (359 ) 0 (138 ) 0 Foreign currency options ( 2) 11 0 (25 ) 0 3 0 Interest rate swaptions (2) 0 0 0 0 4 0 Total fair value hedges (169 ) 0 (384 ) 0 (131 ) 0 Net investment hedge: Non-derivative hedging 0 (15 ) 0 0 0 3 Foreign currency forwards 0 (25 ) 0 (118 ) 0 4 Foreign currency options 0 5 0 73 0 0 Total net investment hedge 0 (35 ) 0 (45 ) 0 7 Non-qualifying strategies: Foreign currency swaps 53 0 117 0 16 0 Foreign currency forwards 8 0 9 0 100 0 Credit default swaps (1 ) 0 2 0 1 0 Interest rate swaps 0 0 0 0 5 0 Futures 0 0 0 0 (1 ) 0 Total non- qualifying strategies 60 0 128 0 121 0 Total $ (109 ) $ (34 ) $ (255 ) $ (42 ) $ (10 ) $ 7 (1) Cash flow hedge items are recorded as unrealized gains (losses) on derivatives and net investment hedge items are recorded in the unrealized foreign currency translation gains (losses) line in the consolidated statement of comprehensive income (loss). (2) Impact shown net of effect of hedged items (see Fair Value Hedges section of this Note 4 for further detail) The Company reclassified an immaterial amount from accumulated other comprehensive income (loss) into earnings related to its designated cash flow hedges for the years ended December 31, 2017, 2016 and 2015, respectively. There was no gain or loss reclassified from accumulated other comprehensive income (loss) into earnings related to the net investment hedge for the years ended December 31, 2017 , 2016 and 2015 . As of December 31, 2017 , deferred gains and losses on derivative instruments recorded in accumulated other comprehensive income that are expected to be reclassified to earnings during the next twelve months were immaterial. Credit Risk Assumed through Derivatives For the foreign currency and credit default swaps associated with the Company's VIE investments for which it is the primary beneficiary, the Company bears the risk of loss due to counterparty default even though it is not a direct counterparty to those contracts. The Company is a direct counterparty to the foreign currency swaps that it has entered into in connection with certain of its senior notes, subordinated debentures; foreign currency forwards; foreign currency options; and interest rate swaptions, and therefore the Company is exposed to credit risk in the event of nonperformance by the counterparties in those contracts. The risk of counterparty default for the Company's foreign currency swaps, certain foreign currency forwards, foreign currency options and interest rate swaptions is mitigated by collateral posting requirements that counterparties to those transactions must meet. As of December 31, 2017 , there were 15 counterparties to the Company's derivative agreements, with four comprising 60% of the aggregate notional amount. The counterparties to these derivatives are financial institutions with the following credit ratings as of December 31: 2017 2016 (In millions) Notional Amount Asset Derivatives Liability Derivatives Notional Amount Asset Derivatives Liability Derivatives Counterparties' credit rating: AA $ 4,708 $ 52 $ (37 ) $ 6,844 $ 247 $ (308 ) A 20,604 271 (370 ) 36,019 900 (1,621 ) BBB 439 8 (67 ) 1,064 60 (69 ) Total $ 25,751 $ 331 $ (474 ) $ 43,927 $ 1,207 $ (1,998 ) The Company engages in derivative transactions directly with unaffiliated third parties under International Swaps and Derivatives Association, Inc. (ISDA) agreements and other documentation. Most of the ISDA agreements also include Credit Support Annexes (CSAs) provisions, which generally provide for two-way collateral postings at the first dollar of exposure. The Company mitigates the risk that counterparties to transactions might be unable to fulfill their contractual obligations by monitoring counterparty credit exposure and collateral value while generally requiring that collateral be posted at the outset of the transaction. In addition, a significant portion of the derivative transactions have provisions that give the counterparty the right to terminate the transaction upon a downgrade of Aflac’s financial strength rating. The actual amount of payments that the Company could be required to make, depends on market conditions, the fair value of outstanding affected transactions, and other factors prevailing at and after the time of the downgrade. Collateral posted by the Company to third parties for derivative transactions can generally be repledged or resold by the counterparties. The aggregate fair value of all derivative instruments with credit-risk-related contingent features that were in a net liability position by counterparty was approximately $264 million and $1.2 billion as of December 31, 2017 and 2016 , respectively. If the credit-risk-related contingent features underlying these agreements had been triggered on December 31, 2017 , the Company estimates that it would be required to post a maximum of $9 million of additional collateral to these derivative counterparties. The Company is generally allowed to sell or repledge collateral obtained from its derivative counterparties, although it does not typically exercise such rights. (See the Offsetting tables below for collateral posted or received as of the reported balance sheet dates.) Offsetting of Financial Instruments and Derivatives Most of the Company's derivative instruments are subject to enforceable master netting arrangements that provide for the net settlement of all derivative contracts between the Parent Company or Aflac and its respective counterparty in the event of default or upon the occurrence of certain termination events. Collateral support agreements with the master netting arrangements generally provide that the Company will receive or pledge financial collateral at the first dollar of exposure. The Company has securities lending agreements with unaffiliated financial institutions that post collateral to the Company in return for the use of its fixed maturity and public equity securities (see Note 3). When the Company has entered into securities lending agreements with the same counterparty, the agreements generally provide for net settlement in the event of default by the counterparty. This right of set-off allows the Company to keep and apply collateral received if the counterparty failed to return the securities borrowed from the Company as contractually agreed. For additional information on the Company's accounting policy for securities lending, see Note 1. The tables below summarize the Company's derivatives and securities lending transactions as of December 31, and as reflected in the tables, in accordance with U.S. GAAP, the Company's policy is to not offset these financial instruments in the Consolidated Balance Sheets. Offsetting of Financial Assets and Derivative Assets 2017 Gross Amounts Not Offset (In millions) Gross Amount of Recognized Assets Gross Amount Offset in Balance Sheet Net Amount of Assets Presented in Balance Sheet Financial Instruments Securities Collateral Cash Collateral Received Net Amount Derivative assets: Derivative assets subject to a master netting agreement or offsetting arrangement $ 180 $ 0 $ 180 $ (82 ) $ 0 $ (98 ) $ 0 Derivative assets not subject to a master netting agreement or offsetting arrangement 151 151 151 Total derivative assets 331 0 331 (82 ) 0 (98 ) 151 Securities lending and similar arrangements 592 0 592 0 0 (592 ) 0 Total $ 923 $ 0 $ 923 $ (82 ) $ 0 $ (690 ) $ 151 2016 Gross Amounts Not Offset (In millions) Gross Amount of Recognized Assets Gross Amount Offset in Balance Sheet Net Amount of Assets Presented in Balance Sheet Financial Instruments Securities Collateral Cash Collateral Received Net Amount Derivative assets: Derivative assets subject to a master netting agreement or offsetting arrangement $ 1,080 $ 0 $ 1,080 $ (698 ) $ 0 $ (382 ) $ 0 Derivative assets not subject to a master netting agreement or offsetting arrangement 127 127 127 Total derivative assets 1,207 0 1,207 (698 ) 0 (382 ) 127 Securities lending and similar arrangements 513 0 513 0 0 (513 ) 0 Total $ 1,720 $ 0 $ 1,720 $ (698 ) $ 0 $ (895 ) $ 127 Offsetting of Financial Liabilities and Derivative Liabilities 2017 Gross Amounts Not Offset in Balance Sheet (In millions) Gross Amount of Recognized Liabilities Gross Amount Offset in Balance Sheet Net Amount of Liabilities Presented in Balance Sheet Financial Instruments Securities Collateral Cash Collateral Pledged Net Amount Derivative liabilities: Derivative liabilities subject to a master netting agreement or offsetting arrangement $ (346 ) $ 0 $ (346 ) $ 82 $ 245 $ 10 $ (9 ) Derivative liabilities not subject to a master netting agreement or offsetting arrangement (128 ) (128 ) (128 ) Total derivative liabilities (474 ) 0 (474 ) 82 245 10 (137 ) Securities lending and similar arrangements (606 ) 0 (606 ) 592 0 0 (14 ) Total $ (1,080 ) $ 0 $ (1,080 ) $ 674 $ 245 $ 10 $ (151 ) 2016 Gross Amounts Not Offset (In millions) Gross Amount of Recognized Liabilities Gross Amount Offset in Balance Sheet Net Amount of Liabilities Presented in Balance Sheet Financial Instruments Securities Collateral Cash Collateral Pledged Net Amount Derivative liabilities: Derivative liabilities subject to a master netting agreement or offsetting arrangement $ (1,852 ) $ 0 $ (1,852 ) $ 698 $ 1,130 $ 21 $ (3 ) Derivative liabilities not subject to a master netting agreement or offsetting arrangement (146 ) (146 ) (146 ) Total derivative liabilities (1,998 ) 0 (1,998 ) 698 1,130 21 (149 ) Securities lending and similar arrangements (526 ) 0 (526 ) 513 0 0 (13 ) Total $ (2,524 ) $ 0 $ (2,524 ) $ 1,211 $ 1,130 $ 21 $ (162 ) For additional information on the Company's financial instruments, see the accompanying Notes 1, 3 and 5.

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
FAIR VALUE MEASUREMENTS	FAIR VALUE MEASUREMENTS Fair Value Hierarchy U.S. GAAP specifies a hierarchy of valuation techniques based on whether the inputs to those valuation techniques are observable or unobservable. These two types of inputs create three valuation hierarchy levels. Level 1 valuations reflect quoted market prices for identical assets or liabilities in active markets. Level 2 valuations reflect quoted market prices for similar assets or liabilities in an active market, quoted market prices for identical or similar assets or liabilities in non-active markets or model-derived valuations in which all significant valuation inputs are observable in active markets. Level 3 valuations reflect valuations in which one or more of the significant inputs are not observable in an active market. The following tables present the fair value hierarchy levels of the Company's assets and liabilities that are measured and carried at fair value on a recurring basis as of December 31. 2017 (In millions) Quoted Prices in Significant Significant Total Assets: Securities available for sale, carried at Fixed maturities: Government and agencies $ 30,109 $ 1,121 $ 0 $ 31,230 Municipalities 0 1,370 0 1,370 Mortgage- and asset-backed securities 0 269 175 444 Public utilities 0 7,886 68 7,954 Sovereign and supranational 0 1,909 0 1,909 Banks/financial institutions 0 7,352 25 7,377 Other corporate 0 32,094 146 32,240 Total fixed maturities 30,109 52,001 414 82,524 Perpetual securities: Banks/financial institutions 0 1,556 0 1,556 Other corporate 0 233 0 233 Total perpetual securities 0 1,789 0 1,789 Equity securities 1,001 6 16 1,023 Other assets: Foreign currency swaps 0 146 150 296 Foreign currency forwards 0 22 0 22 Foreign currency options 0 12 0 12 Credit default swaps 0 0 1 1 Total other assets 0 180 151 331 Other investments 57 0 0 57 Cash and cash equivalents 3,491 0 0 3,491 Total assets $ 34,658 $ 53,976 $ 581 $ 89,215 Liabilities: Other liabilities: Foreign currency swaps $ 0 $ 69 $ 128 $ 197 Foreign currency forwards 0 274 0 274 Foreign currency options 0 3 0 3 Total liabilities $ 0 $ 346 $ 128 $ 474 2016 (In millions) Quoted Prices in Significant Significant Total Assets: Securities available for sale, carried at Fixed maturities: Government and agencies $ 25,387 $ 827 $ 0 $ 26,214 Municipalities 0 1,295 0 1,295 Mortgage- and asset-backed securities 0 1,139 198 1,337 Public utilities 0 7,667 16 7,683 Sovereign and supranational 0 1,469 0 1,469 Banks/financial institutions 0 6,038 25 6,063 Other corporate 0 29,699 0 29,699 Total fixed maturities 25,387 48,134 239 73,760 Perpetual securities: Banks/financial institutions 0 1,420 0 1,420 Other corporate 0 213 0 213 Total perpetual securities 0 1,633 0 1,633 Equity securities 1,300 6 3 1,309 Other assets: Foreign currency swaps 0 365 125 490 Foreign currency forwards 0 672 0 672 Foreign currency options 0 43 0 43 Credit default swaps 0 0 2 2 Total other assets 0 1,080 127 1,207 Other investments 276 0 0 276 Cash and cash equivalents 4,859 0 0 4,859 Total assets $ 31,822 $ 50,853 $ 369 $ 83,044 Liabilities: Other liabilities: Foreign currency swaps $ 0 $ 84 $ 146 $ 230 Foreign currency forwards 0 1,717 0 1,717 Foreign currency options 0 51 0 51 Total liabilities $ 0 $ 1,852 $ 146 $ 1,998 The following tables present the carrying amount and fair value categorized by fair value hierarchy level for the Company's financial instruments that are not carried at fair value as of December 31. 2017 (In millions) Carrying Quoted Prices in Significant Significant Total Assets: Securities held to maturity, Fixed maturities: Government and agencies $ 21,331 $ 26,491 $ 0 $ 0 $ 26,491 Municipalities 357 0 462 0 462 Mortgage and asset-backed 26 0 8 19 27 Public utilities 3,300 0 3,698 0 3,698 Sovereign and 1,523 0 1,835 0 1,835 Banks/financial institutions 2,206 0 2,387 0 2,387 Other corporate 2,687 0 3,172 0 3,172 Other investments (1) 3,017 0 15 2,987 3,002 Total assets $ 34,447 $ 26,491 $ 11,577 $ 3,006 $ 41,074 Liabilities: Other policyholders’ funds $ 6,939 $ 0 $ 0 $ 6,841 $ 6,841 Notes payable 5,267 0 5,288 265 5,553 Total liabilities $ 12,206 $ 0 $ 5,288 $ 7,106 $ 12,394 (1) Excludes policy loans of $210 and equity method investments of $118 , at carrying value 2016 (In millions) Carrying Quoted Prices in Significant Significant Total Assets: Securities held to maturity, Fixed maturities: Government and agencies $ 20,702 $ 26,040 $ 0 $ 0 $ 26,040 Municipalities 350 0 457 0 457 Mortgage and asset-backed 30 0 10 22 32 Public utilities 3,201 0 3,536 0 3,536 Sovereign and 2,602 0 2,877 0 2,877 Banks/financial institutions 3,731 0 3,900 0 3,900 Other corporate 2,734 0 3,179 0 3,179 Other investments 1,174 0 0 1,142 1,142 Total assets $ 34,524 $ 26,040 $ 13,959 $ 1,164 $ 41,163 Liabilities: Other policyholders’ funds $ 6,659 $ 0 $ 0 $ 6,540 $ 6,540 Notes payable 5,339 0 0 5,530 5,530 Total liabilities $ 11,998 $ 0 $ 0 $ 12,070 $ 12,070 Fair Value of Financial Instruments Fixed maturities, perpetual securities, and equity securities The Company determines the fair values of fixed-maturity securities, perpetual securities, and public and privately issued equity securities using the following approaches or techniques: price quotes and valuations from third party pricing vendors (including quoted market prices readily available from public exchange markets) and non-binding price quotes the Company obtains from outside brokers. A third party pricing vendor has developed valuation models to determine fair values of privately issued securities to reflect the impact of the persistent economic environment and the changing regulatory framework. These models are discounted cash flow (DCF) valuation models, but also use information from related markets, specifically the CDS market to estimate expected cash flows. These models take into consideration any unique characteristics of the securities and make various adjustments to arrive at an appropriate issuer-specific loss adjusted credit curve. This credit curve is then used with the relevant recovery rates to estimate expected cash flows and modeling of additional features, including illiquidity adjustments, if necessary, to price the security by discounting those loss adjusted cash flows. In cases where a credit curve cannot be developed from the specific security features, the valuation methodology takes into consideration other market observable inputs, including: 1) the most appropriate comparable security(ies) of the issuer; 2) issuer-specific CDS spreads; 3) bonds or CDS spreads of comparable issuers with similar characteristics such as rating, geography, or sector; or 4) bond indices that are comparative in rating, industry, maturity and region. The pricing data and market quotes the Company obtains from outside sources, including third party pricing services, are reviewed internally for reasonableness. If a fair value appears unreasonable, the Company will re-examine the inputs and assess the reasonableness of the pricing data with the vendor. Additionally, the Company may compare the inputs to relevant market indices and other performance measurements. Based on management's analysis, the valuation is confirmed or may be revised if there is evidence of a more appropriate estimate of fair value based on available market data. The Company has performed verification of the inputs and calculations in any valuation models to confirm that the valuations represent reasonable estimates of fair value. The fixed maturities classified as Level 3 consist of securities with limited or no observable valuation inputs. For Level 3 securities, the Company estimates the fair value of these securities by obtaining non-binding broker quotes from a limited number of brokers. These brokers base their quotes on a combination of their knowledge of the current pricing environment and market conditions. The Company considers these inputs to be unobservable. The Company also considers a variety of significant valuation inputs in the valuation process, including forward exchange rates, yen swap rates, dollar swap rates, interest rate volatilities, credit spread data on specific issuers, assumed default and default recovery rates, and certain probability assumptions. In obtaining these valuation inputs, the Company has determined that certain pricing assumptions and data used by its pricing sources are difficult to validate or corroborate by the market and/or appear to be internally developed rather than observed in or corroborated by the market. The use of these unobservable valuation inputs causes more subjectivity in the valuation process for these securities. For the periods presented, the Company has not adjusted the quotes or prices it obtains from the pricing services and brokers it uses. The following tables present the pricing sources for the fair values of the Company's fixed maturities, perpetual securities, and equity securities as of December 31. 2017 (In millions) Quoted Prices in Active Markets for Identical Assets Significant Observable Inputs Significant Unobservable Inputs Total Securities available for sale, carried at fair value: Fixed maturities: Government and agencies: Third party pricing vendor $ 30,109 $ 1,121 $ 0 $ 31,230 Total government and agencies 30,109 1,121 0 31,230 Municipalities: Third party pricing vendor 0 1,370 0 1,370 Total municipalities 0 1,370 0 1,370 Mortgage- and asset-backed securities: Third party pricing vendor 0 269 0 269 Broker/other 0 0 175 175 Total mortgage- and asset-backed securities 0 269 175 444 Public utilities: Third party pricing vendor 0 7,886 0 7,886 Broker/other 0 0 68 68 Total public utilities 0 7,886 68 7,954 Sovereign and supranational: Third party pricing vendor 0 1,807 0 1,807 Broker/other 0 102 0 102 Total sovereign and supranational 0 1,909 0 1,909 Banks/financial institutions: Third party pricing vendor 0 7,352 0 7,352 Broker/other 0 0 25 25 Total banks/financial institutions 0 7,352 25 7,377 Other corporate: Third party pricing vendor 0 32,094 0 32,094 Broker/other 0 0 146 146 Total other corporate 0 32,094 146 32,240 Total fixed maturities 30,109 52,001 414 82,524 Perpetual securities: Banks/financial institutions: Third party pricing vendor 0 1,556 0 1,556 Total banks/financial institutions 0 1,556 0 1,556 Other corporate: Third party pricing vendor 0 233 0 233 Total other corporate 0 233 0 233 Total perpetual securities 0 1,789 0 1,789 Equity securities: Third party pricing vendor 1,001 6 0 1,007 Broker/other 0 0 16 16 Total equity securities 1,001 6 16 1,023 Total securities available for sale $ 31,110 $ 53,796 $ 430 $ 85,336 2017 (In millions) Quoted Prices in Active Markets for Identical Assets Significant Observable Inputs Significant Unobservable Inputs Total Securities held to maturity, carried at amortized cost: Fixed maturities: Government and agencies: Third party pricing vendor $ 26,491 $ 0 $ 0 $ 26,491 Total government and agencies 26,491 0 0 26,491 Municipalities: Third party pricing vendor 0 462 0 462 Total municipalities 0 462 0 462 Mortgage- and asset-backed securities: Third party pricing vendor 0 8 0 8 Broker/other 0 0 19 19 Total mortgage- and asset-backed securities 0 8 19 27 Public utilities: Third party pricing vendor 0 3,698 0 3,698 Total public utilities 0 3,698 0 3,698 Sovereign and supranational: Third party pricing vendor 0 1,835 0 1,835 Total sovereign and supranational 0 1,835 0 1,835 Banks/financial institutions: Third party pricing vendor 0 2,387 0 2,387 Total banks/financial institutions 0 2,387 0 2,387 Other corporate: Third party pricing vendor 0 3,172 0 3,172 Total other corporate 0 3,172 0 3,172 Total securities held to maturity $ 26,491 $ 11,562 $ 19 $ 38,072 2016 (In millions) Quoted Prices in Active Markets Significant Observable Significant Unobservable Inputs Total Securities available for sale, carried at fair value: Fixed maturities: Government and agencies: Third party pricing vendor $ 25,387 $ 827 $ 0 $ 26,214 Total government and agencies 25,387 827 0 26,214 Municipalities: Third party pricing vendor 0 1,295 0 1,295 Total municipalities 0 1,295 0 1,295 Mortgage- and asset-backed securities: Third party pricing vendor 0 1,139 0 1,139 Broker/other 0 0 198 198 Total mortgage- and asset-backed securities 0 1,139 198 1,337 Public utilities: Third party pricing vendor 0 7,667 0 7,667 Broker/other 0 0 16 16 Total public utilities 0 7,667 16 7,683 Sovereign and supranational: Third party pricing vendor 0 1,469 0 1,469 Total sovereign and supranational 0 1,469 0 1,469 Banks/financial institutions: Third party pricing vendor 0 6,038 0 6,038 Broker/other 0 0 25 25 Total banks/financial institutions 0 6,038 25 6,063 Other corporate: Third party pricing vendor 0 29,699 0 29,699 Total other corporate 0 29,699 0 29,699 Total fixed maturities 25,387 48,134 239 73,760 Perpetual securities: Banks/financial institutions: Third party pricing vendor 0 1,420 0 1,420 Total banks/financial institutions 0 1,420 0 1,420 Other corporate: Third party pricing vendor 0 213 0 213 Total other corporate 0 213 0 213 Total perpetual securities 0 1,633 0 1,633 Equity securities: Third party pricing vendor 1,300 6 0 1,306 Broker/other 0 0 3 3 Total equity securities 1,300 6 3 1,309 Total securities available for sale $ 26,687 $ 49,773 $ 242 $ 76,702 2016 (In millions) Quoted Prices in Active Markets Significant Observable Significant Unobservable Inputs Total Securities held to maturity, carried at amortized cost: Fixed maturities: Government and agencies: Third party pricing vendor $ 26,040 $ 0 $ 0 $ 26,040 Total government and agencies 26,040 0 0 26,040 Municipalities: Third party pricing vendor 0 457 0 457 Total municipalities 0 457 0 457 Mortgage- and asset-backed securities: Third party pricing vendor 0 10 0 10 Broker/other 0 0 22 22 Total mortgage- and asset-backed securities 0 10 22 32 Public utilities: Third party pricing vendor 0 3,536 0 3,536 Total public utilities 0 3,536 0 3,536 Sovereign and supranational: Third party pricing vendor 0 2,877 0 2,877 Total sovereign and supranational 0 2,877 0 2,877 Banks/financial institutions: Third party pricing vendor 0 3,900 0 3,900 Total banks/financial institutions 0 3,900 0 3,900 Other corporate: Third party pricing vendor 0 3,179 0 3,179 Total other corporate 0 3,179 0 3,179 Total securities held to maturity $ 26,040 $ 13,959 $ 22 $ 40,021 The following is a discussion of the determination of fair value of the Company's remaining financial instruments. Derivatives The Company uses derivative instruments to manage the risk associated with certain assets. However, the derivative instrument may not be classified in the same fair value hierarchy level as the associated asset. Inputs used to value derivatives include, but are not limited to, interest rates, credit spreads, foreign currency forward and spot rates, and interest volatility. The fair values of the foreign currency forwards, options, and interest rate swaptions associated with certain investments; the foreign currency forwards and options used to hedge foreign exchange risk from the Company's net investment in Aflac Japan and economically hedge certain portions of forecasted cash flows denominated in yen; and the foreign currency swaps associated with certain senior notes and subordinated debentures are based on the amounts the Company would expect to receive or pay. The determination of the fair value of these derivatives is based on observable market inputs, therefore they are classified as Level 2. For derivatives associated with VIEs where the Company is the primary beneficiary, the Company is not the direct counterparty to the swap contracts. As a result, the fair value measurements incorporate the credit risk of the collateral associated with the VIE. The Company receives valuations from a third party pricing vendor for these derivatives. Based on an analysis of these derivatives and a review of the methodology employed by the pricing vendor, the Company determined that due to the long duration of these swaps and the need to extrapolate from short-term observable data to derive and measure long-term inputs, certain inputs, assumptions and judgments are required to value future cash flows that cannot be corroborated by current inputs or current observable market data. As a result, the derivatives associated with the Company's consolidated VIEs are classified as Level 3 of the fair value hierarchy. Other investments Other investments where fair value is disclosed above include short-term investments and loan receivables. Loan receivables include transitional real estate loans, commercial mortgage loans, and middle market loans. The Company's loan receivables do not have readily determinable market prices and generally lack market liquidity. Fair values for loan receivables are determined based on the present value of expected future cash flows discounted at the applicable U.S. Treasury or London Interbank Offered Rate (LIBOR) yield plus an appropriate spread that considers other risk factors, such as credit and liquidity risk. These spreads are provided by the applicable asset managers based on their knowledge of the current loan pricing environment and market conditions. The spreads are a significant component of the pricing inputs and are generally considered unobservable. Therefore, these investments have been assigned a Level 3 within the fair value hierarchy. Other policyholders' funds The largest component of the other policyholders' funds liability is the Company's annuity line of business in Aflac Japan. The Company's annuities have fixed benefits and premiums. For this product, the Company estimates the fair value to be equal to the cash surrender value. This is analogous to the value paid to policyholders on the valuation date if they were to surrender their policy. The Company periodically checks the cash value against discounted cash flow projections for reasonableness. The Company considers its inputs for this valuation to be unobservable and have accordingly classified this valuation as Level 3. Notes payable As of December 31, 2016, the fair values of the Company's publicly issued notes payable were obtained from a limited number of independent brokers and classified as Level 3 within the fair value hierarchy. However, in 2017 recognizing the similarities of the Company's publicly issued notes payable to fixed income securities in its investment portfolios, the Company aligned the determination of the fair values of these liabilities with its practices of determining asset fair values whereby the Company utilizes available sources of observable inputs from third party pricing vendors; therefore, the fair values of the Company's publicly issued notes payable were reclassified into Level 2 from Level 3 in the first quarter of 2017. The fair values of the Company's yen-denominated loans approximate their carrying values. Transfers between Hierarchy Levels and Level 3 Rollforward There were no transfers between Level 1 and 2 for assets and liabilities that are measured and carried at fair value on a recurring basis for the years ended December 31, 2017 and 2016 , respectively. The following tables present the changes in fair value of the Company's available-for-sale investments and derivatives classified as Level 3 as of December 31. 2017 Fixed Maturities Equity Derivatives (1) (In millions) Mortgage- Public Banks/ Other Foreign Credit Total Balance, beginning of period $ 198 $ 16 $ 25 $ 0 $ 3 $ (21 ) $ 2 $ 223 Realized investment gains (losses) included 0 0 0 0 0 43 (1 ) 42 Unrealized gains (losses) included in other 3 0 0 2 0 0 0 5 Purchases, issuances, sales and settlements: Purchases 0 76 0 122 16 0 0 214 Issuances 0 0 0 0 0 0 0 0 Sales 0 0 0 (2 ) (1 ) 0 0 (3 ) Settlements (26 ) 0 0 0 0 0 0 (26 ) Transfers into Level 3 0 0 0 24 (2) 0 0 0 24 Transfers out of Level 3 0 (24 ) (2) 0 0 (2 ) (3) 0 0 (26 ) Balance, end of period $ 175 $ 68 $ 25 $ 146 $ 16 $ 22 $ 1 $ 453 Changes in unrealized gains (losses) relating $ 0 $ 0 $ 0 $ 0 $ 0 $ 43 $ (1 ) $ 42 (1) Derivative assets and liabilities are presented net (2) Transfer due to sector classification change (3) Transfer due to change in accounting method 2016 Fixed Maturities Equity Derivatives (1) (In millions) Mortgage- Public Banks/ Other Foreign Credit Total Balance, beginning of period $ 220 $ 0 $ 26 $ 0 $ 3 $ (192 ) $ 1 $ 58 Realized investment gains (losses) included in 0 0 0 0 0 194 1 195 Unrealized gains (losses) included in other 38 0 (1 ) 0 0 (22 ) 0 15 Purchases, issuances, sales and settlements: Purchases 0 16 0 0 0 0 0 16 Issuances 0 0 0 0 0 0 0 0 Sales 0 0 0 0 0 0 0 0 Settlements (60 ) 0 0 0 0 (1 ) 0 (61 ) Transfers into Level 3 0 0 0 0 0 0 0 0 Transfers out of Level 3 0 0 0 0 0 0 0 0 Balance, end of period $ 198 $ 16 $ 25 $ 0 $ 3 $ (21 ) $ 2 $ 223 Changes in unrealized gains (losses) relating $ 0 $ 0 $ 0 $ 0 $ 0 $ 194 $ 1 $ 195 (1) Derivative assets and liabilities are presented net Level 3 Significant Unobservable Input Sensitivity The following tables summarize the significant unobservable inputs used in the valuation of the Company's Level 3 available-for-sale investments and derivatives as of December 31. Included in the tables are the inputs or range of possible inputs that have an effect on the overall valuation of the financial instruments. 2017 (In millions) Fair Value Valuation Technique(s) Unobservable Input Range Assets: Securities available for sale, carried at fair value: Fixed maturities: Mortgage- and asset-backed securities $ 175 Consensus pricing Offered quotes N/A (c) Public utilities 68 Discounted cash flow Credit spreads N/A (c) Banks/financial institutions 25 Consensus pricing Offered quotes N/A (c) Other corporate 146 Discounted cash flow Credit spreads N/A (d) Equity securities 16 Net asset value Offered quotes N/A (c) Other assets: Foreign currency swaps 80 Discounted cash flow Interest rates (USD) 2.40% - 2.54% (a) Interest rates (JPY) .26% - .85% (b) CDS spreads 9 - 90 bps 70 Discounted cash flow Interest rates (USD) 2.40% - 2.54% (a) Interest rates (JPY) .26% - .85% (b) Credit default swaps 1 Discounted cash flow Base correlation 46.33% - 49.65% (d) CDS spreads 25 bps Recovery rate 37.24% Total assets $ 581 (a) Inputs derived from U.S. long-term rates to accommodate long maturity nature of the Company's swaps (b) Inputs derived from Japan long-term rates to accommodate long maturity nature of the Company's swaps (c) N/A represents securities where the Company receives unadjusted broker quotes and for which there is no transparency into the providers' valuation techniques or unobservable inputs. (d) Range of base correlation for the Company's bespoke tranche for attachment and detachment points corresponding to market indices 2017 (In millions) Fair Value Valuation Technique(s) Unobservable Input Range Liabilities: Other liabilities: Foreign currency swaps 120 Discounted cash flow Interest rates (USD) 2.40% - 2.54% (a) Interest rates (JPY) .26% - .85% (b) CDS spreads 13 - 157 bps 8 Discounted cash flow Interest rates (USD) 2.40% - 2.54% (a) Interest rates (JPY) .26% - .85% (b) Total liabilities $ 128 (a) Inputs derived from U.S. long-term rates to accommodate long maturity nature of the Company's swaps (b) Inputs derived from Japan long-term rates to accommodate long maturity nature of the Company's swaps 2016 (In millions) Fair Value Valuation Technique(s) Unobservable Input Range Assets: Securities available for sale, carried at fair value: Fixed maturities: Mortgage- and asset-backed securities $ 198 Consensus pricing Offered quotes N/A (d) Public utilities 16 Discounted cash flow Historical volatility N/A (d) Banks/financial institutions 25 Consensus pricing Offered quotes N/A (d) Equity securities 3 Net asset value Offered quotes $1-$701 ($8) Other assets: Foreign currency swaps 16 Discounted cash flow Interest rates (USD) 2.34% - 2.59% (a) Interest rates (JPY) .22% - .80% (b) CDS spreads 17 - 172 bps Foreign exchange rates 21.47% (c) 29 Discounted cash flow Interest rates (USD) 2.34% - 2.59% (a) Interest rates (JPY) .22% - .80% (b) CDS spreads 16 - 88 bps 80 Discounted cash flow Interest rates (USD) 2.34% - 2.59% (a) Interest rates (JPY) .22% - .80% (b) Foreign exchange rates 21.47% (c) Credit default swaps 2 Discounted cash flow Base correlation 52.18% - 56.07% (e) CDS spreads 54 bps Recovery rate 36.69% Total assets $ 369 (a) Inputs derived from U.S. long-term rates to accommodate long maturity nature of the Company's swaps (b) Inputs derived from Japan long-term rates to accommodate long maturity nature of the Company's swaps (c) Based on 10 year volatility of JPY/USD exchange rate (d) N/A represents securities where the Company receives unadjusted broker quotes and for which there is no transparency into the providers' valuation techniques or unobservable inputs. (e) Range of base correlation for the Company's bespoke tranche for attachment and detachment points corresponding to market indices 2016 (In millions) Fair Value Valuation Technique(s) Unobservable Input Range Liabilities: Other liabilities: Foreign currency swaps $ 113 Discounted cash flow Interest rates (USD) 2.34% - 2.59% (a) Interest rates (JPY) .22% - .80% (b) CDS spreads 17 - 172 bps Foreign exchange rates 21.47% (c) 23 Discounted cash flow Interest rates (USD) 2.34% - 2.59% (a) Interest rates (JPY) .22% - .80% (b) CDS spreads 24 - 216 bps 10 Discounted cash flow Interest rates (USD) 2.34% - 2.59% (a) Interest rates (JPY) .22% - .80% (b) Foreign exchange rates 21.47% (c) Total liabilities $ 146 (a) Inputs derived from U.S. long-term rates to accommodate long maturity nature of the Company's swaps (b) Inputs derived from Japan long-term rates to accommodate long maturity nature of the Company's swaps (c) Based on 10 year volatility of JPY/USD exchange rate The following is a discussion of the significant unobservable inputs or valuation techniques used in determining the fair value of securities and derivatives classified as Level 3. Net Asset Value The Company holds certain unlisted equity securities whose fair value is derived based on the financial statements published by the investee. These securities do not trade on an active market and the valuations derived are dependent on the availability of timely financial reporting of the investee. Net asset value is an unobservable input in the determination of fair value of equity securities. Offered Quotes In circumstances where the Company's valuation model price is overridden because it implies a value that is not consistent with current market conditions, the Company will solicit bids from a limited number of brokers. The Company also receives unadjusted prices from brokers for its mortgage and asset-backed securities. These quotes are non-binding but are reflective of valuation best estimates at that particular point in time. Offered quotes are an unobservable input in the determination of fair value of mortgage- and asset-backed securities, certain banks/financial institutions, certain other corporate, and equity securities investments. Interest Rates, CDS Spreads, Foreign Exchange Rates The significant drivers of the valuation of the interest and foreign exchange swaps are interest rates, foreign exchange rates and CDS spreads. The Company's swaps have long maturities that increase the sensitivity of the swaps to interest rate fluctuations. Since most of the Company's yen-denominated cross currency swaps are in a net liability position, an increase in interest rates will decrease the liabilities and increase the value of the swap. Foreign exchange swaps also have a lump-sum final settlement of foreign exchange principal receivables at the termination of the swap. An increase in yen interest rates will decrease the value of the final settlement foreign exchange receivables and decrease the value of the swap, and an increase in U.S. dollar interest rates will increase the swap value. A similar sensitivity pattern is observed for the foreign exchange rates. When the spot U.S. dollar/Japanese yen (USD/JPY) foreign exchange rate decreases and the swap is receiving a final exchange payment in JPY, the swap value will increase due to the appreciation of the JPY. Most of the Company's swaps are designed to receive payments in JPY at the termination and will thus be impacted by the USD/JPY foreign exchange rate in this way. In cases where there is no final foreign exchange receivable in JPY and the Company is paying JPY as interest payments and receiving USD, a decrease in the foreign exchange rate will lead to a decrease in the swap value. The extinguisher feature in most of the Company's VIE swaps results in a cessation of cash flows and no further payments between the parties to the swap in the event of a default on the referenced or underlying collateral. To price this feature, the Company applies the survival probability of the referenced entity to the projected cash flows. The survival probability uses the CDS spreads and recovery rates to adjust the present value of the cash flows. For extinguisher swaps with positive values, an increase in CDS spreads decreases the likelihood of receiving the final exchange payments and reduces the value of the swap. Base Correlations, CDS Spreads, Recovery Rates The Company's remaining collateralized debt obligation (CDO) is a tranche on a basket of single-name credit default swaps. The risk in this synthetic CDO comes from the single-name CDS risk and the correlations between the single names. The valuation of synthetic CDOs is dependent on the calibration of market prices for interest rates, single name CDS default probabilities and base correlation using financial modeling tools. Since there is limited or no observable data available for this tranche, the base correlations must be obtained from commonly traded market tranches such as the CDX and iTraxx indices. From the historical prices of these indices, base correlations can be obtained to develop a pricing curve of CDOs with different seniorities. Since the reference entities of the market indices do not match those in the portfolio underlying the synthetic CDO to be valued, several processing steps are taken to map the CDO in the Company's portfolio to the indices. With the base correlation determined and the appropriate spreads selected, a valuation is calculated. An increase in the CDS spreads in the underlying portfolio leads to a decrease in the value due to higher probability of defaults and losses. The impact on the valuation due to base correlation depends on a number of factors, including the riskiness between market tranches and the modeled tranche based on the Company's portfolio and the equivalence between detachment points in these tranches. Generally speaking, an increase in base correlation will decrease the value of the senior tranches while increasing the value of junior tranches. This may result in a positive or negative value change. The CDO tranche in the Company's portfolio is a senior mezzanine tranche and, due to the low level of credit support for this type of tranche, exhibits equity-like behavior. As a result, an increase in recovery rates tends to cause its value to decrease. Base correlations, CDS spreads, and recovery rates are unobservable inputs in the determination of fair value of credit default swaps. For additional information on the Company's investments and financial instruments, see the accompanying Notes 1, 3 and 4.

DEFERRED POLICY ACQUISITION COS

DEFERRED POLICY ACQUISITION COSTS AND INSURANCE EXPENSES	12 Months Ended
	Dec. 31, 2017
Deferred Policy Acquisition Costs Disclosures [Abstract]
DEFERRED POLICY ACQUISITION COSTS AND INSURANCE EXPENSES	DEFERRED POLICY ACQUISITION COSTS AND INSURANCE EXPENSES Consolidated policy acquisition costs deferred were $1.5 billion in 2017 , compared with $1.4 billion in 2016 and $1.3 billion in 2015 . The following table presents a rollforward of deferred policy acquisition costs by segment for the years ended December 31. 2017 2016 (In millions) Japan U.S. Japan U.S. Deferred policy acquisition costs: Balance, beginning of year $ 5,765 $ 3,228 $ 5,370 $ 3,141 Capitalization 839 629 864 583 Amortization (630 ) (502 ) (644 ) (497 ) Foreign currency translation and other 176 0 175 1 Balance, end of year $ 6,150 $ 3,355 $ 5,765 $ 3,228 Commissions deferred as a percentage of total acquisition costs deferred were 72% in 2017 , compared with 74% in 2016 and 2015 . Personnel, compensation and benefit expenses as a percentage of insurance expenses were 56% in 2017 , compared with 53% in 2016 and 52% in 2015 . Advertising expense, which is included in insurance expenses in the consolidated statements of earnings, was as follows for the years ended December 31: (In millions) 2017 2016 2015 Advertising expense: Aflac Japan $ 100 $ 100 $ 82 Aflac U.S. 110 124 129 Total advertising expense $ 210 $ 224 $ 211 Depreciation and other amortization expenses, which are included in insurance expenses in the consolidated statements of earnings, were as follows for the years ended December 31: (In millions) 2017 2016 2015 Depreciation expense $ 50 $ 48 $ 44 Other amortization expense 3 6 6 Total depreciation and other amortization expense $ 53 $ 54 $ 50 Lease and rental expense, which are included in insurance expenses in the consolidated statements of earnings, were as follows for the years ended December 31: (In millions) 2017 2016 2015 Lease and rental expense: Aflac Japan $ 52 $ 53 $ 46 Aflac U.S. 21 21 18 Other 2 1 1 Total lease and rental expense $ 75 $ 75 $ 65

POLICY LIABILITIES

POLICY LIABILITIES	12 Months Ended
	Dec. 31, 2017
Insurance Loss Reserves [Abstract]
POLICY LIABILITIES	POLICY LIABILITIES Policy liabilities consist of future policy benefits, unpaid policy claims, unearned premiums, and other policyholders' funds, which accounted for 83% , 4% , 6% and 7% of total policy liabilities at December 31, 2017 , respectively. The Company regularly reviews the adequacy of its policy liabilities in total and by component. The liability for future policy benefits as of December 31 consisted of the following: Liability Amounts Interest Rates (In millions) Policy 2017 2016 Year of In 20 Health insurance: Japan: 1992 - 2017 $ 10,167 $ 8,912 1.0 - 2.5 % 1.0 - 2.5 % 1974 - 2013 1,133 1,118 2.7 - 2.75 2.25 - 2.75 1998 - 2017 12,386 11,687 3.0 3.0 1997 - 1999 2,454 2,485 3.5 3.5 1994 - 1996 3,046 3,069 4.0 - 4.5 4.0 - 4.5 1987 - 1994 14,829 14,372 5.5 5.5 1985 - 1991 1,816 1,871 5.25 - 6.75 5.25 - 5.5 1978 - 1984 2,037 2,134 6.5 5.5 U.S.: 2013 - 2017 82 75 3.0 3.0 2012 - 2017 1,366 1,062 3.75 3.75 2011 343 319 4.75 4.75 2005 - 2010 2,944 3,004 5.5 5.5 1988 - 2004 656 669 8.0 6.0 1986 - 2004 1,296 1,265 6.0 6.0 1981 - 1986 159 166 6.5 - 7.0 5.5 - 6.5 1998 - 2004 1,310 1,295 7.0 7.0 Other 18 19 Intercompany eliminations: 2015 (609 ) (1) (630 ) (1) 2.0 2.0 Life insurance: Japan: 2001 - 2017 8,850 7,255 1.0 - 1.85 1.0 - 1.85 2011 - 2017 4,763 4,151 2.0 2.0 2009 - 2011 3,393 2,861 2.25 2.25 1992 - 2006 5 5 2.19 1.55 2005 - 2011 1,642 1,488 2.5 2.5 1985 - 2006 2,048 2,007 2.7 2.25 2007 - 2011 1,319 1,220 2.75 2.75 1999 - 2011 2,189 2,102 3.0 3.0 1996 - 2009 675 657 3.5 3.5 1994 - 1996 908 897 4.0 - 4.5 4.0 - 4.5 U.S.: 1956 - 2017 632 571 3.5 - 6.0 3.5 - 6.0 Total $ 81,857 $ 76,106 (1) Elimination entry necessary due to recapture of a portion of policy liabilities ceded externally, as a result of the reinsurance retrocession transaction as described in Note 8 of the Notes to the Consolidated Financial Statements The weighted-average interest rates reflected in the consolidated statements of earnings for future policy benefits for Japanese policies were 3.4% in 2017 , compared with 3.5% in 2016 and 3.6% in 2015 ; and for U.S. policies, 5.4% in 2017 , compared with 5.5% in 2016 and 5.6% in 2015 . Changes in the liability for unpaid policy claims were as follows for the years ended December 31: (In millions) 2017 2016 2015 Unpaid supplemental health claims, beginning of period $ 3,707 $ 3,548 $ 3,412 Less reinsurance recoverables 27 26 7 Net balance, beginning of period 3,680 3,522 3,405 Add claims incurred during the period related to: Current year 6,979 7,037 6,416 Prior years (518 ) (465 ) (353 ) Total incurred 6,461 6,572 6,063 Less claims paid during the period on claims incurred during: Current year 4,530 4,613 4,227 Prior years 1,822 1,865 1,718 Total paid 6,352 6,478 5,945 Effect of foreign exchange rate changes on unpaid claims 65 64 (1 ) Net balance, end of period 3,854 3,680 3,522 Add reinsurance recoverables 30 27 26 Unpaid supplemental health claims, end of period 3,884 3,707 3,548 Unpaid life claims, end of period 508 338 254 Total liability for unpaid policy claims $ 4,392 $ 4,045 $ 3,802 Total incurred claims decreased from 2016 to 2017 largely due to the weakening of the yen. Excluding the impact of foreign exchange rates, total incurred claims increased due to normal increases in inforce and policyholder aging. The favorable claims development of $518 million for 2017 comprises approximately $383 million from Japan, which represents approximately 74% of the total. Excluding the impact of foreign exchange of a loss of approximately $18 million from December 31, 2016 to December 31, 2017 , the favorable claims development in Japan would have been approximately $400 million , representing approximately 77% of the total. The Company has experienced continued favorable claim trends in 2017 for its core health products in Japan. The Company's experience in Japan related to the average length of stay in the hospital for cancer treatment has shown continued decline in the current period. In addition, cancer treatment patterns in Japan are continuing to be influenced by significant advances in early-detection techniques and by the increased use of pathological diagnosis rather than clinical exams. Additionally, follow-up radiation and chemotherapy treatments are occurring more often on an outpatient basis. Such changes in treatment not only increase the quality of life and initial outcomes for the patients, but also decrease the average length of each hospital stay, resulting in favorable claims development. As of December 31, 2017 and 2016 , unearned premiums consisted primarily of discounted advance premiums on deposit. Discounted advance premiums are premiums on deposit from policyholders in conjunction with their purchase of certain Aflac Japan limited-pay insurance products. These advanced premiums are deferred upon collection and recognized as premium revenue over the contractual premium payment period. These advanced premiums represented 73% of the December 31, 2017 and 76% of the December 31, 2016 unearned premiums balances. As of December 31, 2017 and 2016 , the largest component of the other policyholders' funds liability was the Company's annuity line of business in Aflac Japan. The Company's annuities have fixed benefits and premiums. These annuities represented 98% at both December 31, 2017 and December 31, 2016 of other policyholders' funds liability.

REINSURANCE

REINSURANCE	12 Months Ended
	Dec. 31, 2017
Reinsurance Disclosures [Abstract]
REINSURANCE	REINSURANCE The Company periodically enters into fixed quota-share coinsurance agreements with other companies in the normal course of business. For each of its reinsurance agreements, the Company determines whether the agreement provides indemnification against loss or liability relating to insurance risk in accordance with applicable accounting standards. Reinsurance premiums and benefits paid or provided are accounted for on bases consistent with those used in accounting for the original policies issued and the terms of the reinsurance contracts. Premiums and benefits are reported net of insurance ceded. Effective March 31, 2015, the Company entered into a coinsurance transaction whereby it ceded 30.0% of the sickness hospital benefit of one of Aflac Japan’s closed in-force blocks of business. The Company has an agreement for a $90 million letter of credit as collateral for this reinsurance transaction (see Note 13 for additional information). Effective April 1, 2015, the Company entered into a retrocession coinsurance transaction whereby it assumed 27.0% of the sickness hospital benefit of one of Aflac Japan’s closed in-force blocks of business through its subsidiary CAIC. Effective October 1, 2014 and September 30, 2013, the Company entered into coinsurance reinsurance transactions whereby it ceded 16.7% and 33.3% , respectively, of the hospital benefit of one of Aflac Japan’s closed medical in-force blocks of business. Effective December 31, 2014, the Company entered into a retrocession coinsurance reinsurance transaction whereby it assumed 8.35% of the reinsured hospital benefit of one of Aflac Japan’s closed medical in-force blocks of business through its subsidiary CAIC. For its reinsurance transactions to date, the Company has recorded a deferred profit liability related to reinsurance transactions. The remaining deferred profit liability of $954 million , as of December 31, 2017 , is included in future policy benefits in the consolidated balance sheet and is being amortized into income over the expected lives of the policies. The Company has also recorded a reinsurance recoverable for reinsurance transactions, which is included in other assets in the consolidated balance sheet and had a remaining balance of $908 million and $860 million as of December 31, 2017 and 2016, respectively. The increase in the reinsurance recoverable balance was driven by two aggregating factors: yen strengthening and the growth in reserves related to the business that has been reinsured as the policies age. The spot yen/dollar exchange rate strengthened by approximately 3% and ceded reserves increased approximately 2% from December 31, 2016, to December 31, 2017. The following table reconciles direct premium income and direct benefits and claims to net amounts after the effect of reinsurance for the years ended December 31. (In millions) 2017 2016 Direct premium income $ 18,875 $ 19,592 Ceded to other companies: Ceded Aflac Japan closed blocks (515 ) (560 ) Other (51 ) (48 ) Assumed from other companies: Retrocession activities 216 234 Other 6 7 Net premium income $ 18,531 $ 19,225 Direct benefits and claims $ 12,486 $ 13,240 Ceded benefits and change in reserves for future benefits: Ceded Aflac Japan closed blocks (473 ) (509 ) Eliminations 51 58 Other (44 ) (38 ) Assumed from other companies: Retrocession activities 209 222 Eliminations (51 ) (58 ) Other 3 4 Benefits and claims, net $ 12,181 $ 12,919 These reinsurance transactions are indemnity reinsurance that do not relieve the Company from its obligations to policyholders. In the event that the reinsurer is unable to meet their obligations, the Company remains liable for the reinsured claims. As a part of its capital contingency plan, the Company entered into a committed reinsurance facility agreement on December 1, 2015 in the amount of approximately 110 billion yen. This reinsurance facility agreement was renewed in 2017 and is effective until December 31, 2018. There are also additional commitment periods of a one-year duration each of which are automatically extended unless notification is received from the reinsurer within 60 days prior to the expiration. The reinsurer can withdraw from the committed facility if Aflac‘s Standard and Poor's (S&P) rating drops below BBB-. As of December 31, 2017 , the Company had not executed a reinsurance treaty under this committed reinsurance facility.

NOTES PAYABLE

NOTES PAYABLE	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
NOTES PAYABLE	NOTES PAYABLE A summary of notes payable as of December 31 follows: (In millions) 2017 2016 2.65% senior notes paid February 2017 $ 0 $ 649 2.40% senior notes due March 2020 548 547 4.00% senior notes due February 2022 348 348 3.625% senior notes due June 2023 697 696 3.625% senior notes due November 2024 745 745 3.25% senior notes due March 2025 446 445 2.875% senior notes due October 2026 297 298 6.90% senior notes due December 2039 220 220 6.45% senior notes due August 2040 254 254 4.00% senior notes due October 2046 394 394 5.50% subordinated debentures due September 2052 0 (1) 486 Yen-denominated senior notes and subordinated debentures: .932% senior notes due January 2027 (principal amount 60.0 billion yen) 528 0 2.108% subordinated debentures due October 2047 (principal amount 60.0 billion yen) 526 0 Yen-denominated loans: Variable interest rate loan due September 2021 (.32% in 2017 and .31% in 2016, principal amount 5.0 billion yen) 44 43 Variable interest rate loan due September 2023 (.47% in 2017 and .46% in 2016, principal amount 25.0 billion yen) 220 214 Capitalized lease obligations payable through 2024 22 21 Total notes payable $ 5,289 $ 5,360 (1) Redeemed in November 2017 Amounts in the table above are reported net of debt issuance costs and issuance premiums or discounts, if applicable, that are being amortized over the life of the notes. In October 2017, the Parent Company issued 60.0 billion yen of subordinated debentures through a U.S. public debt offering. The debentures bear interest at an initial rate of 2.108% per annum through October 22, 2027, or earlier redemption. Thereafter, the rate of the interest of the debentures will be reset every five years at a rate of interest equal to the then-current JPY 5-year Swap Offered Rate plus 205 basis points. The debentures are payable semi-annually in arrears and have a 30 -year maturity. The debentures are redeemable (i) at any time, in whole but not in part, upon the occurrence of certain tax events or certain rating agency events, as specified in the indenture governing the terms of the debentures or (ii) on or after October 23, 2027, in whole or in part, at a redemption price equal to their principal amount plus accrued and unpaid interest to, but excluding, the date of redemption. In January 2017, the Parent Company issued 60.0 billion yen of senior notes through a U.S. public debt offering. The notes bear interest at a fixed rate of .932% per annum, payable semi-annually, and have a 10 -year maturity. These notes may only be redeemed before maturity, in whole but not in part, upon the occurrence of certain changes affecting U.S. taxation, as specified in the indenture governing the terms of the issuance. In September 2016, the Parent Company issued two series of senior notes totaling $700 million through a U.S. public debt offering. The first series, which totaled $300 million , bears interest at a fixed rate of 2.875% per annum, payable semi-annually and has a 10 -year maturity. The second series, which totaled $400 million , bears interest at a fixed rate of 4.00% per annum, payable semi-annually, and has a 30 -year maturity. In September 2016, the Parent Company entered into two series of senior unsecured term loan facilities totaling 30.0 billion yen. The first series, which totaled 5.0 billion yen, bears an interest rate per annum equal to the Tokyo interbank market rate (TIBOR), or alternate TIBOR, if applicable, plus the applicable TIBOR margin and has a five-year maturity. The applicable margin ranges between .20% and .60%, depending on the Parent Company's debt ratings as of the date of determination. The second series, which totaled 25.0 billion yen, bears an interest rate per annum equal to TIBOR, or alternate TIBOR, if applicable, plus the applicable TIBOR margin and has a seven-year maturity. The applicable margin ranges between .35% and .75%, depending on the Parent Company's debt ratings as of the date of determination. In March 2015, the Parent Company issued two series of senior notes totaling $1.0 billion through a U.S. public debt offering. The first series, which totaled $550 million , bears interest at a fixed rate of 2.40% per annum, payable semi-annually, and has a five -year maturity. The second series, which totaled $450 million , bears interest at a fixed rate of 3.25% per annum, payable semi-annually, and has a 10 -year maturity. The Parent Company has entered into cross-currency swaps that convert the U.S. dollar-denominated principal and interest on the senior notes into yen-denominated obligations which results in lower nominal net interest rates on the debt. By entering into these cross-currency swaps, the Parent Company economically converted its $550 million liability into a 67.0 billion yen liability and reduced the interest rate on this debt from 2.40% in dollars to .24% in yen, and the Parent Company economically converted its $450 million liability into a 55.0 billion yen liability and reduced the interest rate on this debt from 3.25% in dollars to .82% in yen. In November 2014, the Parent Company issued $750 million of senior notes through a U.S. public debt offering. The notes bear interest at a fixed rate of 3.625% per annum, payable semi-annually, and have a 10 -year maturity. These notes are redeemable at the Parent Company's option in whole at any time or in part from time to time at a redemption price equal to the greater of: (i) the aggregate principal amount of the notes to be redeemed or (ii) the amount equal to the sum of the present values of the remaining scheduled payments for principal of and interest on the notes to be redeemed, not including any portion of the payments of interest accrued as of such redemption date, discounted to such redemption date on a semiannual basis at the treasury rate plus 20 basis points, plus in each case, accrued and unpaid interest on the principal amount of the notes to be redeemed to, but excluding, such redemption date. The Parent Company entered into cross-currency interest rate swaps to reduce interest expense by converting the U.S. dollar-denominated principal and interest on the senior notes it issued into yen-denominated obligations. By entering into the swaps, the Parent Company economically converted its $750 million liability into an 85.3 billion yen liability and reduced the interest rate on this debt from 3.625% in dollars to 1.00% in yen. In June 2013, the Parent Company issued $700 million of senior notes through a U.S. public debt offering. The notes bear interest at a fixed rate of 3.625% per annum, payable semi-annually, and have a 10 -year maturity. These notes are redeemable at the Parent Company's option in whole at any time or in part from time to time at a redemption price equal to the greater of: (i) the aggregate principal amount of the notes to be redeemed or (ii) the amount equal to the sum of the present values of the remaining scheduled payments for principal of and interest on the notes to be redeemed, not including any portion of the payments of interest accrued as of such redemption date, discounted to such redemption date on a semiannual basis at the treasury rate plus 20 basis points, plus in each case, accrued and unpaid interest on the principal amount of the notes to be redeemed to, but excluding, such redemption date. The Parent Company had entered into cross-currency interest rate swaps to reduce interest expense by converting the U.S. dollar-denominated principal and interest on the senior notes it issued into yen-denominated obligations. By entering into these swaps, the Parent Company economically converted its $700 million liability into a 69.8 billion yen liability and reduced the interest rate on this debt from 3.625% in dollars to 1.50% in yen. In September 2012, the Parent Company issued $450 million of subordinated debentures through a U.S. public debt offering. The debentures bore interest at a fixed rate of 5.50% per annum, payable quarterly, and had a 40 -year maturity. The Parent Company had entered into cross-currency interest rate swaps to convert the U.S. dollar-denominated principal and interest on the subordinated debentures it issued into yen-denominated obligations. By entering into these swaps, the Parent Company economically converted its $450 million liability into a 35.3 billion yen liability and reduced the interest rate on this debt from 5.50% in dollars to 4.41% in yen. The swaps expired after the initial five -year non-callable period for the debentures. In October 2012 , the underwriters exercised their option, pursuant to the underwriting agreement, to purchase an additional $50 million principal amount of the debentures discussed above. The Parent Company had entered into a cross-currency interest rate swap to economically convert this $50 million liability into a 3.9 billion yen liability and reduce the interest rate from 5.50% in dollars to 4.42% in yen. The swap expired after the initial five -year non-callable period for the debentures. In November 2017, the Parent Company used a portion of net proceeds from the October 2017 issuance of its subordinated debentures to redeem $500 million of the Parent Company's 5.50% subordinated debentures due 2052. The pretax expense due to the early redemption of these notes was $13 million . In February 2012, the Parent Company issued two series of senior notes totaling $750 million through a U.S. public debt offering. The first series, which totaled $400 million , bears interest at a fixed rate of 2.65% per annum, payable semiannually, and had a five -year maturity. The second series, which totaled $350 million , bears interest at a fixed rate of 4.00% per annum, payable semiannually, and has a 10 -year maturity. These notes are redeemable at the Parent Company's option in whole at any time or in part from time to time at a redemption price equal to the greater of: (i) the principal amount of the notes or (ii) the present value of the remaining scheduled payments of principal and interest to be redeemed, discounted to the redemption date, plus accrued and unpaid interest. The Parent Company entered into cross-currency interest rate swaps to reduce interest expense by converting the U.S. dollar-denominated principal and interest on the senior notes it issued into yen-denominated obligations. By entering into these swaps, the Parent Company economically converted its $400 million liability into a 30.9 billion yen liability and reduced the interest rate on this debt from 2.65% in dollars to 1.22% in yen. The Parent Company also economically converted its $350 million liability into a 27.0 billion yen liability and reduced the interest rate on this debt from 4.00% in dollars to 2.07% in yen. In July 2012, the Parent Company issued $250 million of senior notes that are an addition to the original first series of senior notes issued in February 2012. These notes had a five -year maturity and a fixed rate of 2.65% per annum, payable semiannually. In February 2017, the Parent Company extinguished $650 million of the 2.65% senior notes upon their maturity. In 2010 and 2009, the Parent Company issued senior notes through U.S. public debt offerings; the details of these notes are as follows. In August 2010, the Parent Company issued $450 million of senior notes that have a 30 -year maturity. In December 2009, the Parent Company issued $400 million of senior notes that have a 30 -year maturity. These senior notes pay interest semiannually and are redeemable at the Parent Company's option in whole at any time or in part from time to time at a redemption price equal to the greater of: (i) the principal amount of the notes or (ii) the present value of the remaining scheduled payments of principal and interest to be redeemed, discounted to the redemption date, plus accrued and unpaid interest. In December 2016, the Parent Company completed a tender offer in which it extinguished $176 million principal of its 6.90% senior notes due 2039 and $193 million principal of its 6.45% senior notes due 2040. The pretax loss due to the early redemption of these notes was $137 million . For the Company's yen-denominated notes and loans, the principal amount as stated in dollar terms will fluctuate from period to period due to changes in the yen/dollar exchange rate. The Company has designated the majority of its yen-denominated notes payable as a nonderivative hedge of the foreign currency exposure of the Company's investment in Aflac Japan. The aggregate contractual maturities of notes payable during each of the years after December 31, 2017 , are as follows: (In millions) Long-term Capitalized Total 2018 $ 0 $ 8 $ 8 2019 0 7 7 2020 550 3 553 2021 44 2 46 2022 350 1 351 Thereafter 4,364 1 4,365 Total $ 5,308 $ 22 $ 5,330 A summary of the Company's lines of credit as of December 31, 2017 follows: Borrower Type Original Term Expiration Date Capacity Amount Outstanding Interest Rate on Borrowed Amount Maturity Period Commitment Fee Business Purpose Aflac Incorporated uncommitted bilateral 364 days November 30, 2018 $100 million $0 million The rate quoted by the bank and agreed upon at the time of borrowing Up to 3 months None General corporate purposes Aflac Incorporated unsecured revolving 3 years March 31, 2019, or the date commitments are terminated pursuant to an event of default 100.0 billion yen 0.0 billion yen A rate per annum equal to (a) Tokyo interbank market rate (TIBOR) plus, the alternative applicable TIBOR margin during the availability period from the closing date to the commitment termination date or (b) the TIBOR rate offered by the agent to major banks in yen for the applicable period plus, the applicable alternative TIBOR margin during the term out period No later than .30% to .50%, depending on the Parent Company's debt ratings as of the date of determination General corporate purposes, including a capital contingency plan for the operations of the Parent Company Aflac Incorporated unsecured revolving 5 years September 18, 2020, or the date commitments are terminated pursuant to an event of default 55.0 billion yen, or the equivalent amount in U.S. dollars 0.0 billion yen A rate per annum equal to, at the Company's option, either, (a) London Interbank Offered Rate (LIBOR) adjusted for certain costs or (b) a base rate determined by reference to the highest of (1) the federal funds rate plus 1/2 of 1%, (2) the rate of interest for such day announced by Mizuho Bank, Ltd. as its prime rate, or (3) the eurocurrency rate for an interest period of one month plus 1.00%, in each case plus an applicable margin No later than September 18, 2020 .085% to .225%, depending on the Parent Company's debt ratings as of the date of determination General corporate purposes, including a capital contingency plan for the operations of the Parent Company Aflac Incorporated uncommitted bilateral None specified None specified $50 million $0 million A rate per annum equal to, at the Parent Company's option, either (a) a eurocurrency rate determined by reference to the agent's LIBOR for the interest period relevant to such borrowing or (b) the base rate determined by reference to the greater of (i) the prime rate as determined by the agent, and (ii) the sum of 0.50% and the federal funds rate for such day Up to 3 months None General corporate purposes Aflac (1) uncommitted revolving 364 days November 30, 2018 $250 million $65 million USD three-month LIBOR plus 75 basis points per annum 3 months None General corporate purposes Aflac Incorporated (1) uncommitted revolving 364 days April 2, 2018 37.5 billion yen 0.0 billion yen Three-month TIBOR plus 80 basis points per annum 3 months None General corporate purposes (1) Intercompany credit agreement The Parent Company was in compliance with all of the covenants of its notes payable and lines of credit at December 31, 2017 . No events of default or defaults occurred during 2017 and 2016 .

INCOME TAXES

INCOME TAXES	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES The components of income tax expense (benefit) applicable to pretax earnings for the years ended December 31 were as follows: (In millions) Foreign U.S. Total 2017: Current $ 722 $ (91 ) $ 631 Deferred (24 ) (1,193 ) (1,217 ) Total income tax expense $ 698 $ (1,284 ) $ (586 ) 2016: Current $ 650 $ 234 $ 884 Deferred 136 388 524 Total income tax expense $ 786 $ 622 $ 1,408 2015: Current $ 1,063 $ 225 $ 1,288 Deferred 42 (1 ) 41 Total income tax expense $ 1,105 $ 224 $ 1,329 The Japan income tax rate for the fiscal year 2015 was 30.8% . The rate was reduced to 28.8% for the fiscal year 2016 and 28.2% for the fiscal year 2017. For the United States, the Tax Cuts and Jobs Act (Tax Act) was signed into law on December 22, 2017. Effective January 1, 2018, the Tax Act imposes a broad number of changes in tax law, including the permanent reduction of the U.S. federal statutory corporate income tax rate from 35% to 21% . At December 22, 2017, prior to accounting for the effects of the Tax Act, the Company calculated a reasonable estimate of its deferred tax assets (DTA) to equal $6.2 billion and deferred tax liabilities (DTL) to equal $12.7 billion , resulting in a net deferred tax liability of $6.5 billion . Based on the value of its deferred assets and liabilities as of the December 22, 2017, enactment date, the Company has evaluated the effects of the Tax Act and has concluded that the reduction in the U.S. federal statutory corporate income tax rate from 35% to 21% will necessitate revaluation of its deferred tax assets and liabilities. The Company expects to complete its accounting for the effects of the Tax Act over the measurement period of up to one year from the enactment date, as permitted by SEC Staff Accounting Bulletin No. 118 (SAB 118). As of the enactment date, the Company has determined a reasonable estimate of income tax effects of the Tax Act. The Company’s current estimated provisional amounts for its deferred taxes, including related valuation allowance, result in a reduction of its DTA by approximately $1.0 billion and its DTL by $2.9 billion , for a net DTL reduction of approximately $1.9 billion . The Company believes that these amounts represent reasonable estimates in accordance with SAB 118. The provisions of ASC 740-10, Income Taxes , require that the effects of changes in tax law on deferred taxes be recognized as a component of the income tax provision in the period the tax rate change was enacted. Therefore, the $1.9 billion provisional amount of net DTL reduction has been recorded in the fourth quarter of 2017 as a reduction in the “Income tax expense, Deferred” line item of the Company’s consolidated statement of earnings. The following includes an overview of the existing current and deferred balances for which calculation of income tax effects of the Tax Act has not been completed: Japan deferred tax balances : The Tax Act reduces the tax rate to 21% , effective January 1, 2018. Prior to the reduction in rate, the Japan deferred tax balances were completely offset by an anticipatory foreign tax credit. As a result of the rate reduction, the Japan deferred tax balance will no longer be offset by an anticipatory foreign tax credit as all of the foreign tax credits will be used to offset the U.S. deferred tax balance of the Aflac Japan branch. The Company has not yet completed its analysis of the components of the Japan tax computation, including a complete validation of the Aflac Japan tax basis. Additional time is needed to collect, analyze, and validate the detailed data underlying the deferred tax amounts in the Aflac Japan branch. The Company has currently recorded a provisional amount of $4.5 billion of net DTL related to this item. Valuation allowances : The Company must assess whether its valuation allowance analyses are impacted by various aspects of the Tax Act with a primary focus on any unused anticipatory foreign tax credits. As the Company has recorded provisional amounts related to the Japan deferred tax balances, any corresponding determination of the need for or change in a valuation allowance is also provisional. The Company has recorded a provisional valuation allowance of $.7 billion against its anticipatory foreign tax credit asset. The impact of the Tax Act may differ, possibly materially, from the recorded provisional amounts. As noted above, the provisions of ASC 740-10, Income Taxes , require that the effects of changes in tax law on deferred taxes be recognized as a component of the income tax provision in the period the tax rate change was enacted, even if the deferred taxes are related to items recorded in accumulated other comprehensive income (AOCI). This results in the misalignment between deferred taxes (reflected, net of allowance, at the newly enacted income tax rates) and the corresponding effects of the deferred amounts in AOCI, which are not subject to revaluation as of the enactment date. Therefore, the deferred tax amounts recorded through AOCI and existing at the enactment date of the Tax Act continue to be reflected at the tax rates effective immediately prior to the enactment date, and the amounts recorded in the period between the enactment date and the end of 2017 are reflected at the new rates pursuant to the Tax Act. Income tax expense in the accompanying statements of earnings varies from the amount computed by applying the expected U.S. tax rate of 35% to pretax earnings. The principal reasons for the differences and the related tax effects for the years ended December 31 were as follows: (In millions) 2017 2016 2015 Income taxes based on U.S. statutory rates $ 1,406 $ 1,424 $ 1,352 Write-down of U.S. deferred tax liabilities for tax reform change (1,933 ) 0 0 Utilization of foreign tax credit (27 ) (30 ) (27 ) Nondeductible expenses 10 8 3 Other, net (42 ) 6 1 Income tax expense $ (586 ) $ 1,408 $ 1,329 Total income tax expense for the years ended December 31 was allocated as follows: (In millions) 2017 2016 2015 Statements of earnings $ (586 ) $ 1,408 $ 1,329 Other comprehensive income (loss): Unrealized foreign currency translation gains (losses) during period 52 70 16 Unrealized gains (losses) on investment securities: Unrealized holding gains (losses) on investment 575 962 (931 ) Reclassification adjustment for realized (gains) losses 1 18 21 Unrealized gains (losses) on derivatives during period 0 1 0 Pension liability adjustment during period 3 (16 ) (7 ) Total income tax expense (benefit) related to items of 631 1,035 (901 ) Additional paid-in capital (exercise of stock options) 0 (10 ) 4 Total income taxes $ 45 $ 2,433 $ 432 The income tax effects of the temporary differences that gave rise to deferred income tax assets and liabilities as of December 31 were as follows: (In millions) 2017 2016 Deferred income tax liabilities: Deferred policy acquisition costs $ 3,285 $ 4,065 Unrealized gains and other basis differences on investment securities 2,882 3,056 Premiums receivable 104 130 Policy benefit reserves 3,557 3,303 Total deferred income tax liabilities 9,828 10,554 Deferred income tax assets: Unfunded retirement benefits 8 13 Other accrued expenses 141 39 Policy and contract claims 870 792 Foreign currency loss on Japan branch 67 185 Deferred compensation 155 243 Capital loss carryforwards 0 3 Depreciation 114 88 Anticipatory foreign tax credit 4,504 4,028 Other 57 107 Total deferred income tax assets before valuation allowance 5,916 5,498 Valuation allowance (657 ) 0 Total deferred income tax assets after valuation allowance 5,259 5,498 Net deferred income tax liability 4,569 5,056 Current income tax liability 176 331 Total income tax liability $ 4,745 $ 5,387 The application of U.S. GAAP requires the Company to evaluate the recoverability of deferred tax assets and establish a valuation allowance if necessary to reduce the deferred tax asset to an amount that is more likely than not expected to be realized. As noted above, the Company has determined a $.7 billion valuation allowance against its anticipatory foreign tax credit is necessary. The anticipatory foreign tax credit represents the foreign tax credit the Company will generate from the reversal of Japan deferred tax liabilities in the future. Based upon a review of the Company's anticipated future taxable income, and including all other available evidence, both positive and negative, the Company's management has concluded that, notwithstanding the anticipatory foreign tax credit, it is more likely than not that all other deferred tax assets will be realized. Under U.S. income tax rules, only 35% of non-life operating losses can be offset against life insurance taxable income each year . For current U.S. income tax purposes, there were no unused operating loss carryforwards available to offset against future taxable income. The Company has no capital loss carryforwards available to offset capital gains. The Company files federal income tax returns in the United States and Japan as well as state or prefecture income tax returns in various jurisdictions in the two countries. The Company is currently under audit by the State of Illinois for tax years 2006-2012. There are currently no other open Federal, State, or local U.S. income tax audits. U.S. federal income tax returns for years before 2014 are no longer subject to examination. Japan corporate income tax returns for years before 2016 are no longer subject to examination. Management believes it has established adequate tax liabilities and final resolution of all open audits is not expected to have a material impact on the Company's consolidated financial statements. A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows for the years ended December 31: (In millions) 2017 2016 Balance, beginning of year $ 294 $ 264 Additions for tax positions of prior years 0 33 Reductions for tax positions of prior years (280 ) (3 ) Balance, end of year $ 14 $ 294 Included in the balance of the liability for unrecognized tax benefits at December 31, 2017 , are $13 million of tax positions for which the ultimate deductibility is highly certain, but for which there is uncertainty about the timing of such deductibility, compared with $293 million at December 31, 2016 . Because of the impact of deferred tax accounting, other than interest and penalties, the disallowance of the shorter deductibility period would not affect the annual effective tax rate, but would accelerate the payment of cash to the taxing authority to an earlier period. The Company has accrued approximately $1 million as of December 31, 2017 , for permanent uncertainties, which if reversed would not have a material effect on the annual effective rate. The Company recognizes accrued interest and penalties related to unrecognized tax benefits in income tax expense. The Company recognized approximately $1 million in interest and penalties in 2017 , compared with $13 million in 2016 and $11 million in 2015 . The Company has accrued approximately $2 million for the payment of interest and penalties as of December 31, 2017 , compared with $26 million a year ago. As of December 31, 2017 , there were no material uncertain tax positions for which the total amounts of unrecognized tax benefits will significantly increase or decrease within the next 12 months.

SHAREHOLDERS' EQUITY

SHAREHOLDERS' EQUITY	12 Months Ended
	Dec. 31, 2017
Stockholders' Equity Note [Abstract]
SHAREHOLDERS' EQUITY	SHAREHOLDERS' EQUITY The following table is a reconciliation of the number of shares of the Company's common stock for the years ended December 31. (In thousands of shares) 2017 2016 2015 Common stock - issued: Balance, beginning of period 671,249 669,723 668,132 Exercise of stock options and issuance of restricted shares 1,632 1,526 1,591 Balance, end of period 672,881 671,249 669,723 Treasury stock: Balance, beginning of period 265,439 245,343 225,687 Purchases of treasury stock: Open market 17,755 21,618 21,179 Other 509 330 247 Dispositions of treasury stock: Shares issued to AFL Stock Plan (891) (1,064) (1,209) Exercise of stock options (367) (683) (465) Other (19) (105) (96) Balance, end of period 282,426 265,439 245,343 Shares outstanding, end of period 390,455 405,810 424,380 Outstanding share-based awards are excluded from the calculation of weighted-average shares used in the computation of basic EPS. The following table presents the approximate number of share-based awards to purchase shares, on a weighted-average basis, that were considered to be anti-dilutive and were excluded from the calculation of diluted earnings per share at December 31: (In thousands) 2017 2016 2015 Anti-dilutive share-based awards 255 911 1,862 The weighted-average shares used in calculating earnings per share for the years ended December 31 were as follows: (In thousands of shares) 2017 2016 2015 Weighted-average outstanding shares used for calculating basic EPS 396,021 411,471 430,654 Dilutive effect of share-based awards 2,909 2,450 2,518 Weighted-average outstanding shares used for calculating diluted EPS 398,930 413,921 433,172 Share Repurchase Program: During 2017 , the Company repurchased 17.8 million shares of its common stock in the open market, compared with 21.6 million shares in 2016 and 21.2 million shares in 2015 . In August 2017, the Company's board of directors authorized the purchase of an additional 40 million shares of its common stock. As of December 31, 2017 , a remaining balance of 49.0 million shares of the Company's common stock was available for purchase under share repurchase authorizations by its board of directors. Voting Rights: In accordance with the Parent Company's articles of incorporation, shares of common stock are generally entitled to one vote per share until they have been held by the same beneficial owner for a continuous period of 48 months , at which time they become entitled to 10 votes per share. Reclassifications from Accumulated Other Comprehensive Income The tables below are reconciliations of accumulated other comprehensive income by component for the years ended December 31. Changes in Accumulated Other Comprehensive Income 2017 (In millions) Unrealized Foreign Unrealized Unrealized Pension Total Balance, beginning of period $ (1,983 ) $ 4,805 $ (24 ) $ (168 ) $ 2,630 Other comprehensive 233 1,158 1 (6 ) 1,386 Amounts reclassified from 0 1 0 11 12 Net current-period other 233 1,159 1 5 1,398 Balance, end of period $ (1,750 ) $ 5,964 $ (23 ) $ (163 ) $ 4,028 All amounts in the table above are net of tax. 2016 (In millions) Unrealized Foreign Unrealized Unrealized Pension Liability Adjustment Total Balance, beginning of period $ (2,196 ) $ 2,986 $ (26 ) $ (139 ) $ 625 Other comprehensive 213 1,854 2 (32 ) 2,037 Amounts reclassified from 0 (35 ) 0 3 (32 ) Net current-period other 213 1,819 2 (29 ) 2,005 Balance, end of period $ (1,983 ) $ 4,805 $ (24 ) $ (168 ) $ 2,630 All amounts in the table above are net of tax. 2015 (In millions) Unrealized Foreign Unrealized Unrealized Pension Liability Adjustment Total Balance, beginning of period $ (2,541 ) $ 4,672 $ (26 ) $ (126 ) $ 1,979 Other comprehensive 345 (1,646 ) 0 (13 ) (1,314 ) Amounts reclassified from 0 (40 ) 0 0 (40 ) Net current-period other 345 (1,686 ) 0 (13 ) (1,354 ) Balance, end of period $ (2,196 ) $ 2,986 $ (26 ) $ (139 ) $ 625 All amounts in the table above are net of tax. The tables below summarize the amounts reclassified from each component of accumulated other comprehensive income based on source for the years ended December 31. Reclassifications Out of Accumulated Other Comprehensive Income (In millions) 2017 Details about Accumulated Other Comprehensive Income Components Amount Reclassified from Accumulated Other Comprehensive Income Affected Line Item in the Unrealized gains (losses) on available-for-sale $ 27 Sales and redemptions (29 ) Other-than-temporary impairment (2 ) Total before tax 1 Tax (expense) or benefit (1) $ (1 ) Net of tax Amortization of defined benefit pension items: Actuarial gains (losses) $ (17 ) Acquisition and operating expenses (2) Prior service (cost) credit 0 Acquisition and operating expenses (2) 6 Tax (expense) or benefit (1) $ (11 ) Net of tax Total reclassifications for the period $ (12 ) Net of tax (1) Based on 35% tax rate (2) These accumulated other comprehensive income components are included in the computation of net periodic pension cost (see Note 14 for additional details). (In millions) 2016 Details about Accumulated Other Comprehensive Income Components Amount Reclassified from Accumulated Other Comprehensive Income Affected Line Item in the Unrealized gains (losses) on available-for-sale $ 136 Sales and redemptions (83 ) Other-than-temporary impairment 53 Total before tax (18 ) Tax (expense) or benefit (1) $ 35 Net of tax Amortization of defined benefit pension items: Actuarial gains (losses) $ (15 ) Acquisition and operating expenses (2) Prior service (cost) credit 11 Acquisition and operating expenses (2) 1 Tax (expense) or benefit (1) $ (3 ) Net of tax Total reclassifications for the period $ 32 Net of tax (1) Based on 35% tax rate (2) These accumulated other comprehensive income components are included in the computation of net periodic pension cost (see Note 14 for additional details). (In millions) 2015 Details about Accumulated Other Comprehensive Income Components Amount Reclassified from Accumulated Other Comprehensive Income Affected Line Item in the Unrealized gains (losses) on available-for-sale $ 214 Sales and redemptions (153 ) Other-than-temporary impairment 61 Total before tax (21 ) Tax (expense) or benefit (1) $ 40 Net of tax Amortization of defined benefit pension items: Actuarial gains (losses) $ (17 ) Acquisition and operating expenses (2) Prior service (cost) credit 17 Acquisition and operating expenses (2) 0 Tax (expense) or benefit (1) $ 0 Net of tax Total reclassifications for the period $ 40 Net of tax (1) Based on 35% tax rate (2) These accumulated other comprehensive income components are included in the computation of net periodic pension cost (see Note 14 for additional details).

SHARE-BASED COMPENSATION

SHARE-BASED COMPENSATION	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
SHARE-BASED COMPENSATION	SHARE-BASED COMPENSATION As of December 31, 2017 , the Company has outstanding share-based awards under the Aflac Incorporated Long-Term Incentive Plan (the "Plan"). Share-based awards are designed to reward employees for their long-term contributions to the Company and provide incentives for them to remain with the Company. The number and frequency of share-based awards are based on competitive practices, operating results of the Company, government regulations, and other factors. The Plan, as amended on February 14, 2017, allows for a maximum number of shares issuable over its term of 37.5 million shares including 19 million shares that may be awarded in respect of awards other than options or stock appreciation rights. If any awards granted under the Plan are forfeited or are terminated before being exercised or settled for any reason other than tax forfeiture, then the shares underlying the awards will again be available under the Plan. The Plan allows awards to Company employees for incentive stock options (ISOs), non-qualifying stock options (NQSOs), restricted stock, restricted stock units, and stock appreciation rights. Non-employee directors are eligible for grants of NQSOs, restricted stock, and stock appreciation rights. As of December 31, 2017 , approximately 20.6 million shares were available for future grants under this plan. The ISOs and NQSOs have a term of 10 years, and the share-based awards generally vest upon time-based conditions or time and performance-based conditions. Time-based vesting generally occurs after three years. Performance-based vesting conditions generally include the attainment of goals related to Company financial performance. As of December 31, 2017 , the only performance-based awards issued and outstanding were restricted stock awards. Stock options and stock appreciation rights granted under the amended Plan have an exercise price of at least the fair market value of the underlying stock on the grant date and have an expiration date no later than 10 years from the grant date. Time-based restricted stock awards, restricted stock units and stock options granted after January 1, 2017 generally vest on a ratable basis over three years, and awards granted prior to the amendment vest on a three -year cliff basis. The Compensation Committee of the Board of Directors has the discretion to determine vesting schedules . Share-based awards granted to U.S.-based grantees are settled with authorized but unissued Company stock, while those issued to Japan-based grantees are settled with treasury shares. Summary of Share-Based Compensation Expense Share-based compensation expense consists primarily of expenses for stock options, restricted stock awards (including performance based restricted stock awards), and restricted stock units granted to employees. The following table presents the impact of the expense recognized in connection with share-based awards for the periods ended December 31. (In millions, except for per-share amounts) 2017 2016 2015 Impact on earnings from continuing operations $ 51 $ 68 $ 39 Impact on earnings before income taxes 51 68 39 Impact on net earnings 35 46 27 Impact on net earnings per share: Basic $ .09 $ .11 $ .06 Diluted .09 .11 .06 Stock Options The following table summarizes stock option activity under the the employee stock option plan. (In thousands of shares) Stock Weighted-Average Outstanding at December 31, 2014 9,307 $ 48.84 Granted in 2015 855 61.47 Canceled in 2015 (231 ) 55.70 Exercised in 2015 (2,013 ) 45.15 Outstanding at December 31, 2015 7,918 50.94 Granted in 2016 664 61.39 Canceled in 2016 (181 ) 55.63 Exercised in 2016 (2,061 ) 48.91 Outstanding at December 31, 2016 6,340 52.56 Granted in 2017 313 71.60 Canceled in 2017 (118 ) 49.90 Exercised in 2017 (2,883 ) 60.22 Outstanding at December 31, 2017 3,652 $ 56.05 (In thousands of shares) 2017 2016 2015 Shares exercisable, end of year 2,104 4,493 6,085 The Company estimates the fair value of each stock option granted using the Black-Scholes-Merton multiple option approach. Expected volatility is based on historical periods generally commensurate with the estimated terms of the options. The Company uses historical data to estimate option exercise and termination patterns within the model. Separate groups of employees that have similar historical exercise patterns are stratified and considered separately for valuation purposes. The expected term of options granted is derived from the output of the Company's option model and represents the weighted-average period of time that options granted are expected to be outstanding. The Company bases the risk-free interest rate on the Treasury note rate with a term comparable to that of the estimated term of the options. The weighted-average fair value of options at their grant date was $15.28 per share for 2017 , compared with $12.70 for 2016 and $9.46 in 2015 . The following table presents the assumptions used in valuing options granted during the years ended December 31. 2017 2016 2015 Expected term (years) 5.9 6.4 6.3 Expected volatility 26.0 % 27.0 % 20.0 % Annual forfeiture rate 3.4 3.2 2.8 Risk-free interest rate 2.5 2.2 2.0 Dividend yield 2.5 2.9 2.7 The following table summarizes information about stock options outstanding and exercisable at December 31, 2017 . (In thousands of shares) Options Outstanding Options Exercisable Range of Stock Option Wgtd.-Avg. Wgtd.-Avg. Stock Option Wgtd.-Avg. $ 22.13 - $ 48.56 823 2.5 $ 38.56 823 $ 38.56 49.50 - 57.93 1,034 5.5 55.64 608 54.04 58.08 - 61.81 748 5.5 61.29 234 61.22 61.95 - 71.04 944 7.4 65.69 439 63.06 71.84 - 87.71 103 9.0 73.53 0 0.00 $ 22.13 - $ 87.71 3,652 5.4 $ 56.05 2,104 $ 50.67 The aggregate intrinsic value in the following table represents the total pretax intrinsic value, and is based on the difference between the exercise price of the stock options and the quoted closing common stock price of $87.78 as of December 31, 2017 , for those awards that have an exercise price currently below the closing price. As of December 31, 2017 , the aggregate intrinsic value of stock options outstanding was $116 million , with a weighted-average remaining term of 5.4 years. The total number of in-the-money stock options exercisable as of December 31, 2017 , was 2 million . The aggregate intrinsic value of stock options exercisable at that same date was $78 million , with a weighted-average remaining term of 3.6 years. The following table summarizes stock option activity during the years ended December 31. (In millions) 2017 2016 2015 Total intrinsic value of options exercised $ 87 $ 41 $ 36 Cash received from options exercised 58 68 68 Tax benefit realized as a result of options exercised and 74 45 25 Performance Restricted Stock Awards Under the Plan, the Company grants selected executive officers performance restricted stock awards (PBRS) each February whose vesting is contingent upon meeting various performance goals. PBRS are generally granted at-the-money and contingently cliff vest over a period of three years, generally subject to continued employment. In February 2017, the Company granted 253 thousand performance-based stock awards, which are contingent on the achievement of Company financial performance metrics and market-based conditions. On the date of grant, the Company estimated the fair value of restricted stock awards using a Monte Carlo simulation model. The model discounts the value of the stock at the assumed vesting date based on a risk-free interest rate. Based on estimates of actual performance versus the vesting thresholds, the calculated fair value percentage payout estimate is updated each quarter. Actual performance, including modification for relative total shareholder return, may result in the ultimate award of 0% to 200% percent of the initial number of PBRS issued, with the potential for no award if company performance goals are not achieved during the three-year period. PBRS subject to accelerated vesting at the date of retirement eligibility is recognized over the implicit service period. The Company uses third-party analyses to assist in developing the assumptions used in, as well as calibrating, the Monte Carlo simulation model. The Company is responsible for determining the assumptions used in estimating the fair value of its share-based payment awards. Key assumptions used to value PBRS granted during 2017 follows: (In millions) 2017 Expected volatility (based on Aflac Inc. and peer group historical daily stock price) 16.59 % Expected life from grant date (years) 2.9 Risk-free interest rate (based on U.S. Treasury yields at the date of grant) 1.56 % Restricted Stock Awards and Units The value of restricted stock awards and restricted stock units is based on the fair market value of our common stock at the date of grant. The following table summarizes restricted stock activity during the years ended December 31. (In thousands of shares) Shares Weighted-Average Restricted stock at December 31, 2014 1,880 $ 54.33 Granted in 2015 638 61.51 Canceled in 2015 (145 ) 57.52 Vested in 2015 (558 ) 48.41 Restricted stock at December 31, 2015 1,815 58.42 Granted in 2016 878 61.68 Canceled in 2016 (76 ) 60.65 Vested in 2016 (749 ) 53.68 Restricted stock at December 31, 2016 1,868 61.76 Granted in 2017 559 72.95 Canceled in 2017 (101 ) 64.45 Vested in 2017 (509 ) 62.17 Restricted stock at December 31, 2017 1,817 $ 64.80 As of December 31, 2017 , total compensation cost not yet recognized in the Company's financial statements related to restricted stock awards and restricted stock units was $32 million , of which $12 million ( 377 thousand shares) was related to restricted stock awards with a performance-based vesting condition. The Company expects to recognize these amounts over a weighted-average period of approximately 1.0 years. There are no other contractual terms covering restricted stock awards once vested.

STATUTORY ACCOUNTING AND DIVIDE

STATUTORY ACCOUNTING AND DIVIDEND RESTRICTIONS	12 Months Ended
	Dec. 31, 2017
Insurance [Abstract]
STATUTORY ACCOUNTING AND DIVIDEND RESTRICTIONS	STATUTORY ACCOUNTING AND DIVIDEND RESTRICTIONS The Company's insurance subsidiaries are required to report their results of operations and financial position to state insurance regulatory authorities on the basis of statutory accounting practices prescribed or permitted by such authorities. Statutory accounting practices primarily differ from U.S. GAAP by charging policy acquisition costs to expense as incurred, establishing future policy benefit liabilities using different actuarial assumptions as well as valuing investments and certain assets and accounting for deferred taxes on a different basis. Aflac, the Company's most significant insurance subsidiary, reports statutory financial statements that are prepared on the basis of accounting practices prescribed or permitted by the Nebraska Department of Insurance (NDOI). The NDOI recognizes statutory accounting principles and practices prescribed or permitted by the state of Nebraska for determining and reporting the financial condition and results of operations of an insurance company, and for determining a company's solvency under Nebraska insurance law. The National Association of Insurance Commissioners' (NAIC) Accounting Practices and Procedures Manual (SAP) has been adopted by the state of Nebraska as a component of those prescribed or permitted practices. Additionally, the Director of the NDOI has the right to permit other specific practices which deviate from prescribed practices. Aflac has been given explicit permission by the Director of the NDOI for two such permitted practices. These permitted practices, which do not impact the calculation of net income on a statutory basis or prevent the triggering of a regulatory event in the Company's risk-based capital calculation, are as follows: • Aflac has reported as admitted assets the refundable lease deposits on the leases of commercial office space which house Aflac Japan's sales operations. These lease deposits are unique and part of the ordinary course of doing business in the country of Japan; these assets would be non-admitted under SAP. • Aflac entered into a reinsurance agreement effective March 31, 2015 with a then unauthorized reinsurer. The effective date of this agreement predated the effective date of Nebraska's Amended Credit for Reinsurance statute (44-416) allowing certified reinsurers and also predated the subsequent approval of the agreement's assuming reinsurer as a Certified Reinsurer, which occurred on August 30, 2015 and December 24, 2015, respectively. Aflac has obtained a permitted practice to recognize this treaty and counterparty as a Certified Reinsurer for the purpose of determining the collateral required to receive reinsurance reserve credit. A reconciliation of Aflac's capital and surplus between SAP and practices permitted by the state of Nebraska is shown below: (In millions) 2017 2016 Capital and surplus, Nebraska state basis $ 11,001 $ 11,221 State Permitted Practice: Refundable lease deposits – Japan (43 ) (40 ) Reinsurance - Japan (818 ) (764 ) Capital and surplus, NAIC basis $ 10,140 $ 10,417 As of December 31, 2017 , Aflac's capital and surplus significantly exceeded the required company action level capital and surplus of $1.4 billion . As determined on a U.S. statutory accounting basis, Aflac's net income was $2.6 billion in 2017 , $2.8 billion in 2016 and $2.3 billion in 2015 . Aflac Japan must report its results of operations and financial position to the Japanese Financial Services Agency (FSA) on a Japanese regulatory accounting basis as prescribed by the FSA. Capital and surplus of the Japan branch, based on Japanese regulatory accounting practices, was $6.7 billion at December 31, 2017 , compared with $5.6 billion at December 31, 2016 . Japanese regulatory accounting practices differ in many respects from U.S. GAAP. Under Japanese regulatory accounting practices, policy acquisition costs are expensed immediately; policy benefit and claim reserving methods and assumptions are different; premium income is recognized on a cash basis; different consolidation criteria apply to VIEs; reinsurance is recognized on a different basis; and investments can have a separate accounting classification and treatment referred to as policy reserve matching bonds (PRM). The Parent Company depends on its subsidiaries for cash flow, primarily in the form of dividends and management fees. Consolidated retained earnings in the accompanying financial statements largely represent the undistributed earnings of the Company's insurance subsidiary. Amounts available for dividends, management fees and other payments to the Parent Company by its insurance subsidiary may fluctuate due to different accounting methods required by regulatory authorities. These payments are also subject to various regulatory restrictions and approvals related to safeguarding the interests of insurance policyholders. The Company's insurance subsidiary must maintain adequate risk-based capital for U.S. regulatory authorities and its Japan branch must maintain adequate solvency margins for Japanese regulatory authorities. Additionally, the maximum amount of dividends that can be paid to the Parent Company by Aflac without prior approval of Nebraska's director of insurance is the greater of the net income from operations, which excludes net realized investment gains, for the previous year determined under statutory accounting principles, or 10% of statutory capital and surplus as of the previous year-end. Dividends declared by Aflac during 2018 in excess of $2.6 billion would require such approval. Aflac declared dividends of $2.6 billion during 2017 . A portion of Aflac Japan earnings, as determined on a Japanese regulatory accounting basis, can be repatriated each year to Aflac U.S. after complying with solvency margin provisions and satisfying various conditions imposed by Japanese regulatory authorities for protecting policyholders. Profit repatriations to the United States can fluctuate due to changes in the amounts of Japanese regulatory earnings. Among other items, factors affecting regulatory earnings include Japanese regulatory accounting practices and fluctuations in currency translation of Aflac Japan's U.S. dollar-denominated investments and related investment income into yen. Profits repatriated by Aflac Japan to Aflac U.S. were as follows for the years ended December 31: In Dollars In Yen (In millions of dollars and billions of yen) 2017 2016 2015 2017 2016 2015 Profit repatriation $ 1,150 $ 1,286 $ 2,139 129.3 138.5 259.0 The Company entered into foreign exchange forwards and options as part of an economic hedge on foreign exchange risk on 90.9 billion yen of profit repatriation received in 2017 , resulting in $1 million less funds received when the yen were exchanged into dollars relative to what would have been received at the then-current exchange rate. As of December 31, 2017 , the Company had foreign exchange forwards and options as part of a hedging strategy on 49.5 billion yen of future profit repatriation.

BENEFIT PLANS

BENEFIT PLANS	12 Months Ended
	Dec. 31, 2017
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract]
BENEFIT PLANS	BENEFIT PLANS Pension and Other Postretirement Plans The Company has funded defined benefit plans in Japan and the United States, however the U.S. plan was frozen to new participants effective October 1, 2013. The Company also maintains non-qualified, unfunded supplemental retirement plans that provide defined pension benefits in excess of limits imposed by federal tax law for certain Japanese, U.S. and former employees, however the U.S. plan was frozen to new participants effective January 1, 2015. U.S. employees who are not participants in the defined benefit plan receive a nonelective 401(k) employer contribution. The Company provides certain health care benefits for eligible U.S. retired employees, their beneficiaries and covered dependents ("other postretirement benefits"). The health care plan is contributory and unfunded. Effective January 1, 2014, employees eligible for benefits included the following: (1) active employees whose age plus service, in years, equaled or exceeded 80 (rule of 80 ); (2) active employees who were age 55 or older and have met the 15 years of service requirement; (3) active employees who would meet the rule of 80 in the next five years ; (4) active employees who were age 55 or older and who would meet the 15 years of service requirement within the next five years ; and (5) current retirees. For certain employees and former employees, additional coverage is provided for all medical expenses for life. Information with respect to the Company's benefit plans' assets and obligations as of December 31 was as follows: Pension Benefits Other Japan U.S. Postretirement Benefits (In millions) 2017 2016 2017 2016 2017 2016 Projected benefit obligation: Benefit obligation, beginning of year $ 329 $ 276 $ 798 $ 735 $ 37 $ 40 Service cost 20 16 24 23 0 1 Interest cost 6 9 40 29 1 2 Actuarial (gain) loss (10 ) 29 65 29 0 (4 ) Benefits and expenses paid (14 ) (8 ) (19 ) (18 ) (2 ) (2 ) Effect of foreign exchange 10 7 0 0 0 0 Benefit obligation, end of year 341 329 908 798 36 37 Plan assets: Fair value of plan assets, 229 198 359 336 0 0 Actual return on plan assets 16 9 61 24 0 0 Employer contributions 32 25 47 17 2 2 Benefits and expenses paid (14 ) (8 ) (19 ) (18 ) (2 ) (2 ) Effect of foreign exchange 7 5 0 0 0 0 Fair value of plan assets, end of year 270 229 448 359 0 0 Funded status of the plans (1) $ (71 ) $ (100 ) $ (460 ) $ (439 ) $ (36 ) $ (37 ) Amounts recognized in accumulated other Net actuarial (gain) loss $ 44 $ 67 $ 203 $ 189 $ 6 $ 7 Prior service (credit) cost (2 ) (2 ) (4 ) (4 ) 0 0 Total included in accumulated $ 42 $ 65 $ 199 $ 185 $ 6 $ 7 Accumulated benefit obligation $ 307 $ 288 $ 756 $ 670 N/A (2) N/A (2) (1) Recognized in other liabilities in the consolidated balance sheets (2) Not applicable Pension Benefits Other Japan U.S. Postretirement Benefits 2017 2016 2015 2017 2016 2015 2017 2016 2015 Weighted-average actuarial assumptions: Discount rate - net periodic benefit cost 1.25 % 1.75 % 1.75 % 4.25 % 4.50 % 4.50 % 4.25 % 4.50 % 4.50 % Discount rate - benefit obligations 1.25 1.25 1.75 3.75 4.25 4.50 3.75 4.25 4.50 Expected long-term return on plan assets 2.00 2.00 2.00 6.75 7.00 7.25 N/A (1) N/A (1) N/A (1) Rate of compensation increase N/A (1) N/A (1) N/A (1) 4.00 4.00 4.00 N/A (1) N/A (1) N/A (1) Health care cost trend rates N/A (1) N/A (1) N/A (1) N/A (1) N/A (1) N/A (1) 5.40 (2) 5.20 (2) 5.30 (2) (1) Not applicable (2) For the years 2017 , 2016 and 2015 , the health care cost trend rates are expected to trend down to 4.5% in 77 years , 4.5% in 74 years , and 4.5% in 78 years , respectively. The Company determines its discount rate assumption for its pension retirement obligations based on indices for AA corporate bonds with an average duration of approximately 20 years for the Japan pension plans and 17 years for the U.S. pension plans, and determination of the U.S. pension plans discount rate utilizes the 85 -year extrapolated yield curve. In Japan, participant salary and future salary increases are not factors in determining pension benefit cost or the related pension benefit obligation. The Company bases its assumption for the long-term rate of return on assets on historical trends ( 10 -year or longer historical rates of return for the Japanese plan assets and 15 -year historical rates of return for the U.S. plan assets), expected future market movement, as well as the portfolio mix of securities in the asset portfolio including, but not limited to, style, class and equity and fixed income allocations. In addition, the Company's consulting actuaries evaluate its assumptions for long-term rates of return under Actuarial Standards of Practice (ASOP). Under the ASOP, the actual portfolio type, mix and class is modeled to determine a best estimate of the long-term rate of return. The Company in turn use those results to further validate its own assumptions. Assumed health care cost trend rates have a significant effect on the amounts reported for the health care plan. A one-percentage point increase and decrease in assumed health care cost trend rates would have the following effects as of December 31, 2017 : (In millions) One percentage point increase: Increase in total service and interest costs $ 0 Increase in postretirement benefit obligation 2 One percentage point decrease: Decrease in total service and interest costs $ 0 Decrease in postretirement benefit obligation 2 Components of Net Periodic Benefit Cost Pension and other postretirement benefit expenses are included in acquisition and operating expenses in the consolidated statements of earnings, which includes $35 million , $17 million and $(5) million of other components of net periodic pension cost and postretirement costs (other than services costs) for the years ended December 31, 2017, 2016 and 2015, respectively. Total net periodic benefit cost includes the following components: Pension Benefits Other Japan U.S. Postretirement Benefits (In millions) 2017 2016 2015 2017 2016 2015 2017 2016 2015 Service cost $ 20 $ 16 $ 15 $ 24 $ 23 $ 23 $ 0 $ 1 $ 1 Interest cost 6 9 1 40 29 18 1 2 2 Expected return on plan (5 ) (4 ) (4 ) (24 ) (23 ) (22 ) 0 0 0 Amortization of net actuarial 2 1 1 14 13 14 1 1 2 Amortization of prior service 0 0 0 0 0 0 0 (11 ) (17 ) Net periodic (benefit) cost $ 23 $ 22 $ 13 $ 54 $ 42 $ 33 $ 2 $ (7 ) $ (12 ) Changes in Accumulated Other Comprehensive Income The following table summarizes the amounts recognized in other comprehensive loss (income) for the years ended December 31: Pension Benefits Other Japan U.S. Postretirement Benefits (In millions) 2017 2016 2015 2017 2016 2015 2017 2016 2015 Net actuarial loss (gain) $ (21 ) $ 26 $ 3 $ 28 $ 27 $ 22 $ 0 $ (4 ) $ (5 ) Amortization of net actuarial loss (2 ) (1 ) (1 ) (14 ) (13 ) (14 ) (1 ) (1 ) (2 ) Amortization of prior 0 0 0 0 0 0 0 11 17 Total $ (23 ) $ 25 $ 2 $ 14 $ 14 $ 8 $ (1 ) $ 6 $ 10 No transition obligations arose during 2017 , and the transition obligations amortized to expense were immaterial for the years ended December 31, 2017 , 2016 and 2015 . Amortization of actuarial losses to expense in 2018 is estimated to be $1 million for the Japanese plans, $16 million for the U.S. plans and $1 million for the other postretirement benefits plan. Amortization of prior service costs and credits and transition obligations for all plans is expected to be negligible in 2018 . Benefit Payments The following table provides expected benefit payments, which reflect expected future service, as appropriate. Pension Benefits Other (In millions) Japan U.S. Postretirement Benefits 2018 $ 10 $ 23 $ 2 2019 11 24 3 2020 12 25 3 2021 12 26 3 2022 18 35 3 2023-2027 82 184 17 Funding The Company plans to make contributions of $34 million to the Japanese funded defined benefit plan and $10 million to the U.S. funded defined benefit plan in 2018 . The funding policy for the Company's non-qualified supplemental defined benefit pension plans and other postretirement benefits plan is to contribute the amount of the benefit payments made during the year. Plan Assets The investment objective of the Company's Japanese and U.S. funded defined benefit plans is to preserve the purchasing power of the plan's assets and earn a reasonable inflation-adjusted rate of return over the long term. Furthermore, the Company seeks to accomplish these objectives in a manner that allows for the adequate funding of plan benefits and expenses. In order to achieve these objectives, the Company's goal is to maintain a conservative, well-diversified and balanced portfolio of high-quality equity, fixed-income and money market securities. As a part of its strategy, the Company has established strict policies covering quality, type and concentration of investment securities. For the Company's Japanese plan, these policies include limitations on investments in derivatives including futures, options and swaps, and low-liquidity investments such as real estate, venture capital investments, and privately issued securities. For the Company's U.S. plan, these policies prohibit investments in precious metals, limited partnerships, venture capital, and direct investments in real estate. The Company is also prohibited from trading on margin. The plan fiduciaries for the Company's funded defined benefit plans have developed guidelines for asset allocations reflecting a percentage of total assets by asset class, which are reviewed on an annual basis. Asset allocation targets as of December 31, 2017 were as follows: Japan Pension U.S. Pension Domestic equities 11 % 40 % International equities 15 20 Fixed income securities 59 40 Other 15 0 Total 100 % 100 % The following table presents the fair value of Aflac Japan's pension plan assets that are measured at fair value on a recurring basis as of December 31. All of these assets are classified as Level 2 in the fair value hierarchy, except cash and cash equivalents which are classified as Level 1. (In millions) 2017 2016 Japan pension plan assets: Equities: Japanese equity securities $ 37 $ 28 International equity securities 50 40 Fixed income securities: Japanese bonds 91 79 International bonds 62 55 Insurance contracts 30 27 Cash and cash equivalents 0 0 Total $ 270 $ 229 The following table presents the fair value of Aflac U.S.'s pension plan assets that are measured at fair value on a recurring basis as of December 31. All of these assets are classified as Level 1 in the fair value hierarchy. (In millions) 2017 2016 U.S. pension plan assets: Mutual funds: Large cap equity funds $ 124 $ 104 Mid cap equity funds 22 19 Real estate equity funds 13 10 International equity funds 108 85 Fixed income bond funds 175 136 Aflac Incorporated common stock 5 4 Cash and cash equivalents 1 1 Total $ 448 $ 359 The fair values of the Company's pension plan investments categorized as Level 1, consisting of mutual funds and common stock, are based on quoted market prices for identical securities traded in active markets that are readily and regularly available to the Company. The fair values of the Company's pension plan investments classified as Level 2 are based on quoted prices for similar assets in markets that are not active, other inputs that are observable, such as interest rates, yield curves, volatilities, prepayment speeds, loss severities, credit risks, and default rates, or other market-corroborated inputs. 401(k) Plan The Company sponsors a 401(k) plan in which it matches a portion of U.S. employees' contributions. The plan provides for salary reduction contributions by employees and, in 2017 , 2016 , and 2015 , provided matching contributions by the Company of 50% of each employee's contributions which were not in excess of 6% of the employee's annual cash compensation. On January 1, 2014, the Company began providing a nonelective contribution to the 401(k) plan of 2% of annual cash compensation for employees who elected to opt out of the future benefits of the U.S. defined benefit plan during the election period provided during the fourth quarter of 2013 and for new U.S. employees who started working for the Company after September 30, 2013. The 401(k) contributions by the Company, included in acquisition and operating expenses in the consolidated statements of earnings, were $15 million in 2017 , $11 million in 2016 and $9 million in 2015 . The plan trustee held approximately one million shares of the Company's common stock for plan participants at December 31, 2017 . As a result of U.S. tax reform legislation enacted in December 2017, the Company announced it would make a one-time contribution of $500 to the 401(k) plan to all employees active on December 31, 2017. This contribution was made by January 31, 2018. The Company also announced that it would increase its matching contributions to 100% of each employee's contributions which were not in excess of 4% of the employee's annual cash compensation. This increase became effective on January 1, 2018. Stock Bonus Plan Aflac U.S. maintains a stock bonus plan for eligible U.S. sales associates. Plan participants receive shares of Aflac Incorporated common stock based on their new annualized premium sales and their first-year persistency of substantially all new insurance policies. The cost of this plan, which was capitalized as deferred policy acquisition costs, amounted to $31 million in both 2017 and 2016 , compared with $34 million in 2015 .

COMMITMENTS AND CONTINGENT LIAB

COMMITMENTS AND CONTINGENT LIABILITIES	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENT LIABILITIES	COMMITMENTS AND CONTINGENT LIABILITIES The Company has two outsourcing agreements with a technology and consulting corporation. The first agreement provides mainframe computer operations, distributed mid-range server computer operations, and related support for Aflac Japan. It has a remaining term of three years and an aggregate remaining cost of 27.5 billion yen ( $243 million using the December 31, 2017 , exchange rate). The second agreement provides application maintenance and development services for Aflac Japan. It has a remaining term of four years and an aggregate remaining cost of 9.0 billion yen ( $80 million using the December 31, 2017 , exchange rate). The Company has an outsourcing agreement with a management consulting and technology services company to provide application maintenance and development services for its Japanese operation. The agreement has a remaining term of four years with an aggregate remaining cost of 14.0 billion yen ( $124 million using the December 31, 2017 , exchange rate). The Company has two outsourcing agreements with information technology and data services companies to provide application maintenance and development services for its Japanese operation. The first agreement has a remaining term of two years with an aggregate remaining cost of 3.0 billion yen ( $26 million using the December 31, 2017 , exchange rate). The second agreement has a remaining term of five years with an aggregate remaining cost of 7.4 billion yen ( $65 million using the December 31, 2017 , exchange rate). The Company leases office space and equipment under agreements that expire in various years through 2028 . Future minimum lease payments due under non-cancelable operating leases at December 31, 2017 , were as follows: (In millions) 2018 $ 61 2019 33 2020 24 2021 21 2022 16 Thereafter 30 Total future minimum lease payments $ 185 The Company is a defendant in various lawsuits considered to be in the normal course of business. Members of the Company's senior legal and financial management teams review litigation on a quarterly and annual basis. The final results of any litigation cannot be predicted with certainty. Although some of this litigation is pending in states where large punitive damages, bearing little relation to the actual damages sustained by plaintiffs, have been awarded in recent years, the Company believes the outcome of pending litigation will not have a material adverse effect on its financial position, results of operations, or cash flows. Guaranty Fund Assessments The United States insurance industry has a policyholder protection system that is monitored and regulated by state insurance departments. These life and health insurance guaranty associations are state entities (in all 50 states as well as Puerto Rico and the District of Columbia) created to protect policyholders of an insolvent insurance company. All insurance companies (with limited exceptions) licensed to sell life or health insurance in a state must be members of that state’s guaranty association. Under state guaranty association laws, certain insurance companies can be assessed (up to prescribed limits) for certain obligations to the policyholders and claimants of impaired or insolvent insurance companies that write the same line or similar lines of business. In 2009, the Pennsylvania Insurance Commissioner placed long-term care insurer Penn Treaty Network America Insurance Company and its subsidiary American Network Insurance Company (collectively referred to as Penn Treaty), neither of which is affiliated with Aflac, in rehabilitation and petitioned a state court for approval to liquidate Penn Treaty. A final order of liquidation was granted by a recognized judicial authority on March 1, 2017, and as a result, Penn Treaty is in the process of liquidation. The Company estimated and recognized the impact of its share of guaranty fund assessments resulting from the liquidation using a discounted rate of 4.25% . The Company recognized a discounted liability for the assessments of $62 million (undiscounted $94 million ), offset by discounted premium tax credits of $48 million (undiscounted $74 million ), for a net $14 million impact to net income in the quarter ended March 31, 2017. The Company paid a majority of these assessments during the past year. A majority of the resulting tax credits will be realized over the next five years. The Company used the cost estimate provided as of the liquidation date by the National Organization of Life and Health Guaranty Associations (NOLHGA) to calculate its estimated assessments and tax credits. Other guaranty fund assessments for the years ended December 31, 2017, 2016, and 2015 were immaterial.

UNAUDITED CONSOLIDATED QUARTERL

UNAUDITED CONSOLIDATED QUARTERLY FINANCIAL DATA	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
UNAUDITED CONSOLIDATED QUARTERLY FINANCIAL DATA	UNAUDITED CONSOLIDATED QUARTERLY FINANCIAL DATA In management's opinion, the following quarterly financial information fairly presents the results of operations for such periods and is prepared on a basis consistent with the Company's annual audited financial statements. (In millions, except for per-share amounts) March 31, June 30, September 30, December 31, Net premium income $ 4,638 $ 4,665 $ 4,648 $ 4,580 Net investment income 794 802 811 812 Realized investment gains (losses) (140 ) (56 ) 30 15 Other income (loss) 17 17 17 17 Total revenues 5,309 5,428 5,506 5,424 Total benefits and expenses 4,411 4,383 4,431 4,425 Earnings before income taxes 898 1,045 1,075 999 Total income tax 306 332 359 (1,585 ) Net earnings $ 592 $ 713 $ 716 $ 2,584 Net earnings per basic share $ 1.48 $ 1.80 $ 1.81 $ 6.59 Net earnings per diluted share 1.47 1.79 1.80 6.54 Quarterly amounts may not agree in total to the corresponding annual amounts due to rounding. (In millions, except for per-share amounts) March 31, June 30, September 30, December 31, Net premium income $ 4,602 $ 4,823 $ 5,022 $ 4,778 Net investment income 801 822 842 813 Realized investment gains (losses) 30 (223 ) (164 ) 344 Other income (loss) 18 15 16 20 Total revenues 5,451 5,437 5,716 5,955 Total benefits and expenses 4,334 4,603 4,753 4,802 Earnings before income taxes 1,117 834 963 1,153 Total income tax 386 286 334 402 Net earnings $ 731 $ 548 $ 629 $ 751 Net earnings per basic share $ 1.75 $ 1.33 $ 1.54 $ 1.85 Net earnings per diluted share 1.74 1.32 1.53 1.84 Quarterly amounts may not agree in total to the corresponding annual amounts due to rounding.

SUBSEQUENT EVENTS

SUBSEQUENT EVENTS	12 Months Ended
	Dec. 31, 2017
Subsequent Events [Abstract]
SUBSEQUENT EVENTS	SUBSEQUENT EVENTS On February 13, 2018, the Board of Directors of the Parent Company declared a two -for-one stock split of the Company’s common stock in the form of a 100% stock dividend payable on March 16, 2018 to shareholders of record at the close of business on March 2, 2018. The stock split will be payable in the form of one additional common stock share for every share of common stock held. The pro forma diluted earnings per common share attributable to Aflac Incorporated shareholders in this note have been adjusted to reflect the stock split for all periods presented. All other share-based data, including the number of shares outstanding and related prices, per share amounts, and share authorizations and conversions have not been adjusted to reflect the stock split for any of the periods presented. As of December 31, 2017, the Company had outstanding approximately 390.5 million shares of common stock. Upon completion of the split, the outstanding shares of common stock will increase to approximately 781.0 million shares. Years ended December 31, Unaudited pro forma 2017 2016 2015 Diluted earnings per common share attributable to Aflac Incorporated shareholders, adjusted for the two-for-one stock split $ 5.77 $ 3.21 $ 2.93

SCHEDULE II CONDENSED FINANCIAL

SCHEDULE II CONDENSED FINANCIAL INFORMATION OF REGISTRANT	12 Months Ended
	Dec. 31, 2017
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
SCHEDULE II CONDENSED FINANCIAL INFORMATION OF REGISTRANT	SCHEDULE II CONDENSED FINANCIAL INFORMATION OF REGISTRANT Aflac Incorporated (Parent Only) Condensed Statements of Earnings Years ended December 31, (In millions) 2017 2016 2015 Revenues: Management and service fees from subsidiaries (1) $ 297 $ 265 $ 260 Net investment income 30 18 22 Interest from subsidiaries (1) 5 5 6 Realized investment gains (losses) 67 84 86 Change in fair value of the cross-currency interest rate swaps (68 ) (159 ) (53 ) Total revenues 331 213 321 Operating expenses: Interest expense 197 213 231 Other operating expenses (2) 180 277 321 Total operating expenses 377 490 552 Earnings before income taxes and equity in earnings of (46 ) (277 ) (231 ) Income tax expense (benefit) (23 ) (102 ) (80 ) Earnings before equity in earnings of subsidiaries (23 ) (175 ) (151 ) Equity in earnings of subsidiaries (1) 4,627 2,834 2,684 Net earnings $ 4,604 $ 2,659 $ 2,533 (1) Eliminated in consolidation (2) Includes expense of $13 in 2017, $137 in 2016 and $230 in 2015 for the early extinguishment of debt See the accompanying Notes to Condensed Financial Statements. See the accompanying Report of Independent Registered Public Accounting Firm. SCHEDULE II CONDENSED FINANCIAL INFORMATION OF REGISTRANT Aflac Incorporated (Parent Only) Condensed Statements of Comprehensive Income (Loss) Years ended December 31, (In millions) 2017 2016 2015 Net earnings $ 4,604 $ 2,659 $ 2,533 Other comprehensive income (loss) before income taxes: Unrealized foreign currency translation gains (losses) during period 286 283 360 Unrealized gains (losses) on investment securities during period 1,733 2,799 (2,595 ) Unrealized gains (losses) on derivatives during period 1 3 0 Pension liability adjustment during period 9 (45 ) (20 ) Total other comprehensive income (loss) before 2,029 3,040 (2,255 ) Income tax expense (benefit) related to items of other comprehensive 631 1,035 (901 ) Other comprehensive income (loss), net of income taxes 1,398 2,005 (1,354 ) Total comprehensive income (loss) $ 6,002 $ 4,664 $ 1,179 See the accompanying Notes to Condensed Financial Statements. See the accompanying Report of Independent Registered Public Accounting Firm. SCHEDULE II CONDENSED FINANCIAL INFORMATION OF REGISTRANT Aflac Incorporated (Parent Only) Condensed Balance Sheets December 31, (In millions, except for share and per-share amounts) 2017 2016 Assets: Investments and cash: Fixed maturity securities available for sale, at fair value $ 1,213 $ 496 Investments in subsidiaries (1) 26,869 23,353 Other investments 51 3 Cash and cash equivalents 1,725 2,037 Total investments and cash 29,858 25,889 Due from subsidiaries (1) 90 75 Income taxes receivable 121 103 Other assets 366 497 Total assets $ 30,435 $ 26,564 Liabilities and shareholders' equity: 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 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 (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) Eliminated in consolidation See the accompanying Notes to Condensed Financial Statements. See the accompanying Report of Independent Registered Public Accounting Firm. SCHEDULE II CONDENSED FINANCIAL INFORMATION OF REGISTRANT Aflac Incorporated (Parent Only) Condensed Statements of Cash Flows Years ended December 31, (In millions) 2017 2016 2015 Cash flows from operating activities: Net earnings $ 4,604 $ 2,659 $ 2,533 Adjustments to reconcile net earnings to net cash provided from Equity in earnings of subsidiaries (1) (4,627 ) (2,834 ) (2,684 ) Cash dividends received from subsidiaries 2,001 2,020 2,393 Other, net (46 ) 294 (2) 155 (2) Net cash provided (used) by operating activities 1,932 2,139 2,397 Cash flows from investing activities: Fixed maturity securities sold 263 225 121 Fixed maturity securities purchased (329 ) (229 ) (202 ) Other investments sold (purchased) (47 ) 6 14 Settlement of derivatives 223 0 147 Additional capitalization of subsidiaries (1) (69 ) (36 ) (43 ) Other, net (218 ) (25 ) 0 Net cash provided (used) by investing activities (177 ) (59 ) 37 Cash flows from financing activities: Purchases of treasury stock (1,351 ) (1,422 ) (1,315 ) Proceeds from borrowings 1,040 986 998 Principal payments under debt obligations (1,161 ) (621 ) (1,272 ) Dividends paid to shareholders (661 ) (658 ) (656 ) Treasury stock reissued 33 46 36 Proceeds from exercise of stock options 38 36 47 Net change in amount due to/from subsidiaries (1) (5 ) (6 ) 43 Other, net 0 (125 ) (2) (232 ) (2) Net cash provided (used) by financing activities (2,067 ) (1,764 ) (2,351 ) Net change in cash and cash equivalents (312 ) 316 83 Cash and cash equivalents, beginning of period 2,037 1,721 1,638 Cash and cash equivalents, end of period $ 1,725 $ 2,037 $ 1,721 (1) Eliminated in consolidation (2) Operating activities excludes and financing activities includes a cash outflow of $137 in 2016 and $230 in 2015 for the payments associated with the early extinguishment of debt See the accompanying Notes to Condensed Financial Statements. See the accompanying Report of Independent Registered Public Accounting Firm. (A) Notes Payable A summary of notes payable as of December 31 follows: (In millions) 2017 2016 2.65% senior notes paid February 2017 $ 0 $ 649 2.40% senior notes due March 2020 548 547 4.00% senior notes due February 2022 348 348 3.625% senior notes due June 2023 697 696 3.625% senior notes due November 2024 745 745 3.25% senior notes due March 2025 446 445 2.875% senior notes due October 2026 297 298 6.90% senior notes due December 2039 220 220 6.45% senior notes due August 2040 254 254 4.00% senior notes due October 2046 394 394 5.50% subordinated debentures due September 2052 0 (1) 486 Yen-denominated senior notes and subordinated debentures: .932% senior notes due January 2027 (principal amount 60.0 billion yen) 528 0 2.108% subordinated debentures due October 2047 (principal amount 60.0 billion 526 0 Yen-denominated loans: Variable interest rate loan due September 2021 (.32% in 2017 and .31% in 2016, 44 43 Variable interest rate loan due September 2023 (.47% in 2017 and .46% in 2016, 220 214 Total notes payable $ 5,267 $ 5,339 (1) Redeemed in November 2017 Amounts in the table above are reported net of debt issuance costs and issuance premiums or discounts, if applicable, that are being amortized over the life of the notes. In January 2017, the Parent Company issued 60.0 billion yen of senior notes through a U.S. public debt offering. The notes bear interest at a fixed rate of .932% per annum, payable semi-annually, and have a 10 -year maturity. These notes may only be redeemed before maturity, in whole but not in part, upon the occurrence of certain changes affecting U.S. taxation, as specified in the indenture governing the terms of the issuance. In February 2017, the Parent Company extinguished $650 million of its 2.65% senior notes upon their maturity. In October 2017, the Parent Company issued 60.0 billion yen of subordinated debentures through a U.S. public debt offering. The debentures bear interest at an initial rate of 2.108% per annum through October 22, 2027, or earlier redemption. Thereafter, the rate of the interest of the debentures will be reset every five years at a rate of interest equal to the then-current JPY 5-year Swap Offered Rate plus 205 basis points. The debentures are payable semi-annually in arrears and have a 30 -year maturity. The debentures are redeemable (i) at any time, in whole but not in part, upon the occurrence of certain tax events or certain rating agency events, as specified in the indenture governing the terms of the debentures or (ii) on or after October 23, 2027, in whole or in part, at a redemption price equal to their principal amount plus accrued and unpaid interest to, but excluding, the date of redemption. In November 2017, the Parent Company used a portion of net proceeds from the October 2017 issuance of subordinated debentures to redeem $500 million of the Parent Company's 5.50% subordinated debentures due 2052. The aggregate contractual maturities of notes payable during each of the years after December 31, 2017 , are as follows: (In millions) 2018 $ 0 2019 0 2020 550 2021 44 2022 350 Thereafter 4,364 Total $ 5,308 For further information regarding notes payable, see Note 9 of the Notes to the Consolidated Financial Statements. (B) Derivatives At December 31, 2017 , the Parent Company's outstanding freestanding derivative contracts were swaps associated with its notes payable, consisting of cross-currency interest rate swaps, also referred to as foreign currency swaps, associated with the Parent Company's senior notes due in March 2020, February 2022, June 2023, November 2024 and March 2025. The Parent Company does not use derivative financial instruments for trading purposes, nor does it engage in leveraged derivative transactions. For further information regarding these derivatives, see Notes 1, 4 and 9 of the Notes to the Consolidated Financial Statements. (C) Income Taxes The Parent Company and its eligible U.S. subsidiaries file a consolidated U.S. federal income tax return. Income tax liabilities or benefits are recorded by each principal subsidiary based upon separate return calculations, and any difference between the consolidated provision and the aggregate amounts recorded by the subsidiaries is reflected in the Parent Company financial statements. For further information on income taxes, see Note 10 of the Notes to the Consolidated Financial Statements. (D) Dividend Restrictions See Note 13 of the Notes to the Consolidated Financial Statements for information regarding dividend restrictions. (E) Supplemental Disclosures of Cash Flow Information (In millions) 2017 2016 2015 Interest paid $ 195 $ 209 $ 235 Noncash financing activities: Treasury stock issued for shareholder dividend reinvestment 29 26 26

SCHEDULE III SUPPLEMENTARY INSU

SCHEDULE III SUPPLEMENTARY INSURANCE INFORMATION	12 Months Ended
	Dec. 31, 2017
Supplementary Insurance Information [Abstract]
SCHEDULE III SUPPLEMENTARY INSURANCE INFORMATION	SCHEDULE III SUPPLEMENTARY INSURANCE INFORMATION Aflac Incorporated and Subsidiaries Years ended December 31, (In millions) Deferred Policy Future Policy Unearned Other 2017: Aflac Japan $ 6,150 $ 76,353 $ 5,840 $ 6,939 Aflac U.S. 3,355 10,506 119 0 All other 0 138 0 0 Intercompany eliminations 0 (748 ) 0 0 Total $ 9,505 $ 86,249 $ 5,959 $ 6,939 2016: Aflac Japan $ 5,765 $ 70,684 $ 6,798 $ 6,659 Aflac U.S. 3,228 10,094 118 0 All other 0 91 0 0 Intercompany eliminations 0 (718 ) 0 0 Total $ 8,993 $ 80,151 $ 6,916 $ 6,659 Segment amounts may not agree in total to the corresponding consolidated amounts due to rounding. Years Ended December 31, (In millions) Net Net Benefits and Amortization of Other Premiums 2017: Aflac Japan $ 12,752 $ 2,463 $ 9,087 $ 630 $ 2,257 $ 12,092 Aflac U.S. 5,563 721 2,885 502 1,658 5,565 All other 216 36 209 0 421 0 Total $ 18,531 $ 3,220 $ 12,181 $ 1,132 $ 4,336 $ 17,657 2016: Aflac Japan $ 13,537 $ 2,554 $ 9,828 $ 644 $ 2,326 $ 12,762 Aflac U.S. 5,454 703 2,869 497 1,593 5,452 All other 234 21 222 0 513 0 Total $ 19,225 $ 3,278 $ 12,919 $ 1,141 $ 4,432 $ 18,214 2015: Aflac Japan $ 12,046 $ 2,436 $ 8,705 $ 578 $ 2,055 $ 11,740 Aflac U.S. 5,347 678 2,873 488 1,570 5,343 All other 177 21 168 0 573 0 Total $ 17,570 $ 3,135 $ 11,746 $ 1,066 $ 4,198 $ 17,083 Segment amounts may not agree in total to the corresponding consolidated amounts due to rounding. See the accompanying Report of Independent Registered Public Accounting Firm.

SCHEDULE IV REINSURANCE

SCHEDULE IV REINSURANCE	12 Months Ended
	Dec. 31, 2017
Reinsurance Disclosures [Abstract]
SCHEDULE IV REINSURANCE	SCHEDULE IV REINSURANCE Aflac Incorporated and Subsidiaries Years Ended December 31, (In millions) Gross Ceded to Assumed Net Percentage 2017: Life insurance in force $ 152,502 $ 4,121 $ 0 $ 148,381 0 % Premiums: Health insurance $ 14,829 $ 554 $ 222 $ 14,497 1 % Life insurance 4,046 12 0 4,034 0 Total earned premiums $ 18,875 $ 566 $ 222 $ 18,531 1 % 2016: Life insurance in force $ 151,093 $ 3,741 $ 0 $ 147,352 0 % Premiums: Health insurance $ 14,839 $ 595 $ 241 $ 14,485 1 % Life insurance 4,753 13 0 4,740 0 Total earned premiums $ 19,592 $ 608 $ 241 $ 19,225 1 % 2015: Life insurance in force $ 146,610 $ 3,547 $ 0 $ 143,063 0 % Premiums: Health insurance $ 13,604 $ 509 $ 186 $ 13,281 1 % Life insurance 4,300 11 0 4,289 0 Total earned premiums $ 17,904 $ 520 $ 186 $ 17,570 1 % Premiums by type may not agree in total to the corresponding consolidated amounts due to rounding. See the accompanying Report of Independent Registered Public Accounting Firm.

SUMMARY OF SIGNIFICANT ACCOUN29

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	12 Months Ended
	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of Business and Basis of Presentation	Description of Business   Aflac Incorporated (the Parent Company) and its subsidiaries (collectively, the Company) primarily sell supplemental health and life insurance in the United States and Japan. The Company's insurance business is marketed and administered through American Family Life Assurance Company of Columbus (Aflac), which operates in the United States (Aflac U.S.) and as a branch in Japan (Aflac Japan). American Family Life Assurance Company of New York (Aflac New York) is a wholly owned subsidiary of Aflac. Most of Aflac's policies are individually underwritten and marketed through independent agents. Additionally, Aflac U.S. markets and administers group products through Continental American Insurance Company (CAIC), branded as Aflac Group Insurance. The Company's insurance operations in the United States and its branch in Japan service the two markets for the Company's insurance business. Aflac Japan's revenues, including realized gains and losses on its investment portfolio, accounted for 70% of the Company's total revenues in 2017 , compared with 71% in 2016 and 70% in 2015 . The percentage of the Company's total assets attributable to Aflac Japan was 83% at December 31, 2017 and 2016 . Basis of Presentation The Company prepares its financial statements in accordance with U.S. generally accepted accounting principles (GAAP). These principles are established primarily by the Financial Accounting Standards Board (FASB). In these Notes to the Consolidated Financial Statements, references to U.S. GAAP issued by the FASB are derived from the FASB Accounting Standards Codification TM (ASC). The preparation of financial statements in conformity with U.S. GAAP requires the Company to make estimates based on currently available information when recording transactions resulting from business operations. The most significant items on the Company's balance sheet that involve a greater degree of accounting estimates and actuarial determinations subject to changes in the future are the valuation of investments and derivatives, deferred policy acquisition costs (DAC), liabilities for future policy benefits and unpaid policy claims, and income taxes. These accounting estimates and actuarial determinations are sensitive to market conditions, investment yields, mortality, morbidity, commission and other acquisition expenses, and terminations by policyholders. As additional information becomes available, or actual amounts are determinable, the recorded estimates will be revised and reflected in operating results. Although some variability is inherent in these estimates, the Company believes the amounts provided are adequate. The consolidated financial statements include the accounts of the Parent Company, its subsidiaries, and those entities required to be consolidated under applicable accounting standards. All material intercompany accounts and transactions have been eliminated.
Translation of Foreign Currencies	Translation of Foreign Currencies:  The functional currency of Aflac Japan's insurance operations is the Japanese yen. The Company translates its yen-denominated financial statement accounts into U.S. dollars as follows. Assets and liabilities are translated at end-of-period exchange rates. Realized gains and losses on security transactions are translated at the exchange rate on the trade date of each transaction. Other revenues, expenses, and cash flows are translated using average exchange rates for the period. The resulting currency translation adjustments are reported in accumulated other comprehensive income. The Company includes in earnings the realized currency exchange gains and losses resulting from foreign currency transactions. The Parent Company has designated a majority of its yen-denominated liabilities (notes payable and yen-denominated loans) as non-derivative hedges and designated certain foreign currency forwards and options as derivative hedges of the foreign currency exposure of the Company's net investment in Aflac Japan. Outstanding principal and related accrued interest on these Parent Company liabilities and the fair value of these derivatives are translated into U.S. dollars at end-of-period exchange rates. Currency translation adjustments and changes in the fair value of these derivatives are recorded as unrealized foreign currency translation gains (losses) in other comprehensive income and are included in accumulated other comprehensive income.
Insurance Revenue and Expense Recognition	Insurance Revenue and Expense Recognition:  The supplemental health and life insurance policies the Company issues are classified as long-duration contracts. The contract provisions generally cannot be changed or canceled during the contract period; however, the Company may adjust premiums for supplemental health policies issued in the United States within prescribed guidelines and with the approval of state insurance regulatory authorities. Insurance premiums for most of the Company's health and life policies, including cancer, accident, hospital, critical illness, dental, vision, term life, whole life, long-term care and disability, are recognized as revenue over the premium-paying periods of the contracts when due from policyholders. When revenues are reported, the related amounts of benefits and expenses are charged against such revenues, so that profits are recognized in proportion to premium revenues during the period the policies are expected to remain in force. This association is accomplished by means of annual additions to the liability for future policy benefits and the deferral and subsequent amortization of policy acquisition costs. Premiums from the Company's products with limited-pay features, including term life, whole life, WAYS, and child endowment, are collected over a significantly shorter period than the period over which benefits are provided. Premiums for these products are recognized as revenue over the premium-paying periods of the contracts when due from policyholders. Any gross premium in excess of the net premium is deferred and recorded in earnings, such that profits are recognized in a constant relationship with insurance in force. Benefits are recorded as an expense when they are incurred. A liability for future policy benefits is recorded when premiums are recognized using the net premium method. At the policyholder's option, customers can also pay discounted advanced premiums for certain of the Company's products. Advanced premiums are deferred and recognized when due from policyholders over the regularly scheduled premium payment period. The calculation of DAC and the liability for future policy benefits requires the use of estimates based on sound actuarial valuation techniques. For new policy issues, the Company reviews its actuarial assumptions and deferrable acquisition costs each year and revises them when necessary to more closely reflect recent experience and studies of actual acquisition costs. For policies in force, the Company evaluates DAC by major product groupings to determine that they are recoverable from future revenues, and any amounts determined not to be recoverable are charged against net earnings. The Company has not had any material charges to earnings for DAC that was determined not to be recoverable in any of the years presented in this Form 10-K.
Advertising Cost, Policy, Expensed Advertising Cost	Advertising expense is reported as incurred in insurance expenses in the consolidated statements of earnings.
Cash and Cash Equivalents	Cash and Cash Equivalents:  Cash and cash equivalents include cash on hand, money market instruments, and other debt instruments with a maturity of 90 days or less when purchased.
Investments	Investments:  The Company's debt securities consist of fixed-maturity securities, which are classified as either held to maturity or available for sale. Securities classified as held to maturity are securities that the Company has the ability and intent to hold to maturity or redemption and are carried at amortized cost. All other fixed-maturity debt securities, perpetual securities, and equity securities are classified as available for sale and are carried at fair value. If the fair value is higher than the amortized cost for debt and perpetual securities, or the purchase cost for equity securities, the excess is an unrealized gain, and if lower than cost, the difference is an unrealized loss. The net unrealized gains and losses on securities available for sale, less related deferred income taxes, are recorded through other comprehensive income and included in accumulated other comprehensive income. Amortized cost of debt and perpetual securities is based on the Company's purchase price adjusted for accrual of discount, or amortization of premium, and recognition of impairment charges, if any. The amortized cost of debt and perpetual securities the Company purchases at a discount or premium will equal the face or par value at maturity or the call date, if applicable. Interest is reported as income when earned and is adjusted for amortization of any premium or discount. The Company has investments in variable interest entities (VIEs). Criteria for evaluating VIEs for consolidation focuses on identifying which enterprise has the power to direct the activities of a variable interest entity that most significantly impact the entity's economic performance and (1) the obligation to absorb losses of the entity or (2) the right to receive benefits from the entity. The Company is the primary beneficiary of certain VIEs, and therefore consolidates these entities in its financial statements. While the consolidated VIEs generally operate within a defined set of documents, there are certain powers that are retained by the Company that are considered significant in the conclusion that the Company is the primary beneficiary. These powers vary by structure but generally include the initial selection of the underlying collateral or, for collateralized debt obligations (CDOs), the reference credits to include in the structure; the ability to obtain the underlying collateral in the event of default; and, the ability to appoint or dismiss key parties in the structure. In particular, the Company's powers surrounding the underlying collateral were considered to be the most significant powers since those most significantly impact the economics of the VIE. The Company has no obligation to provide any continuing financial support to any of the entities in which it is the primary beneficiary. The Company's maximum loss is limited to its original investment. Neither the Company nor any of its creditors has the ability to obtain the underlying collateral, nor does the Company have control over the instruments held in the VIEs, unless there is an event of default. For those entities where the Company is the primary beneficiary, the assets consolidated are segregated on the balance sheet by the caption "consolidated variable interest entities," and consist of fixed-maturity securities, perpetual securities, equity securities, loan receivables, and derivative instruments. For the mortgage- and asset-backed securities held in the Company's fixed maturities portfolio, the Company recognizes income using a constant effective yield, which is based on anticipated prepayments and the estimated economic life of the securities. When estimates of prepayments change, the effective yield is recalculated to reflect actual payments to date and anticipated future payments. The net investment in mortgage- and asset-backed securities is adjusted to the amount that would have existed had the new effective yield been applied at the time of acquisition. This adjustment is reflected in net investment income. The Company uses the specific identification method to determine the gain or loss from securities transactions and report the realized gain or loss in the consolidated statements of earnings. Securities transactions are accounted for based on values as of the trade date of the transaction. An investment in a fixed maturity, perpetual security, or equity security is impaired if the fair value falls below book value. The Company regularly reviews its entire investment portfolio for declines in value. The Company's fixed maturities and investment-grade perpetual securities investments are evaluated for other-than-temporary impairment using its debt impairment model. The Company's debt impairment model focuses on the ultimate collection of the cash flows from its investments and whether the Company has the intent to sell or if it is more likely than not the Company would be required to sell the security prior to recovery of its amortized cost. The determination of the amount of impairments under this model is based upon the Company's periodic evaluation and assessment of known and inherent risks associated with the respective securities. Such evaluations and assessments are revised as conditions change and new information becomes available. When determining the Company's intention to sell a security prior to recovery of its fair value to amortized cost, the Company evaluates facts and circumstances such as, but not limited to, future cash flow needs, decisions to reposition its security portfolio, and risk profile of individual investment holdings. The Company performs ongoing analyses of its liquidity needs, which includes cash flow testing of its policy liabilities, debt maturities, projected dividend payments, and other cash flow and liquidity needs. The Company's cash flow testing includes extensive duration analysis of its investment portfolio and policy liabilities. Based on the Company's analyses, the Company has concluded that it has sufficient excess cash flows to meet its liquidity needs without selling any of its investments prior to their maturity. The determination of whether an impairment in value of the Company's fixed maturity securities is other than temporary is based largely on the Company's evaluation of the issuer ' s creditworthiness. The Company must apply considerable judgment in determining the likelihood of its fixed maturity securities recovering in value. Factors that may influence this include the overall level of interest rates, credit spreads, the credit quality of the underlying issuer, and other factors. This process requires consideration of risks which can be controlled to a certain extent, such as credit risk, and risks which cannot be controlled, such as interest rate risk and foreign currency risk. If, after monitoring and analyses, management believes that fair value will not recover to amortized cost prior to the disposal of the security, the Company recognizes an other-than-temporary impairment of the security. Once a security is considered to be other-than-temporarily impaired, the impairment loss is separated into two separate components: the portion of the impairment related to credit and the portion of the impairment related to factors other than credit. The Company recognizes a charge to earnings for the credit-related portion of other-than-temporary impairments. Impairments related to factors other than credit are charged to earnings in the event the Company intends to sell the security prior to the recovery of its amortized cost or if it is more likely than not that the Company would be required to dispose of the security prior to recovery of its amortized cost; otherwise, non-credit-related other-than-temporary impairments are charged to other comprehensive income. The Company's investments in perpetual securities that are rated below investment grade and equity securities are evaluated for other-than-temporary impairment under the Company's equity impairment model. The Company's equity impairment model focuses on the severity of a security's decline in fair value coupled with the length of time the fair value of the security has been below amortized cost and the financial condition and near-term prospects of the issuer. For equity securities that have declines in value that are deemed to be temporary, the Company makes an assertion as to its ability and intent to retain the security until recovery. Once identified, these equity securities are restricted from trading unless authorized based upon significant events that could not have been foreseen at the time the Company asserted its ability and intent to retain the security until recovery. If management believes that the equity security will not recover prior to the disposal of the security, the Company recognizes an other-than-temporary impairment of the security. Once an equity security is considered to be other-than-temporarily impaired, its fair value on that date becomes the new cost basis and the impairment loss is recognized in earnings. The Company lends fixed-maturity securities to financial institutions in short-term security lending transactions. These securities continue to be carried as investment assets on the Company's balance sheet during the terms of the loans and are not reported as sales. The Company receives cash or other securities as collateral for such loans. For loans involving unrestricted cash or securities as collateral, the collateral is reported as an asset with a corresponding liability for the return of the collateral. Other investments include transitional real estate loans (TREs), commercial mortgage loans (CMLs), middle market loans (MMLs), policy loans, limited partnerships, and other short-term investments with maturities of one year or less, but greater than 90 days, at the time of purchase. The Company invests in TREs, CMLs, and MMLs that are accounted for as loan receivables and recorded at amortized cost on the acquisition date. Since the Company has the intent and ability to hold these loan receivables for the foreseeable future or until they mature, they are considered held for investment and are carried at adjusted amortized cost in the other investments line on its consolidated balance sheets. The adjusted amortized cost of the loan receivables reflects allowances for expected incurred losses estimated based on past events and current economic conditions as of each reporting date. Limited partnership investments are accounted for using the equity method of accounting. Under the equity method of accounting, the Company reports its portion of partnership earnings as a component of net investment income in its consolidated statements of earnings. The underlying investments held by the Company’s limited partnerships primarily consist of private equity. Other short-term investments are stated at amortized cost, which approximates estimated fair value.
Derivatives and Hedging	Derivatives and Hedging:  Freestanding derivative instruments are reported in the consolidated balance sheet at fair value and are reported in other assets and other liabilities, with changes in value reported in earnings and/or other comprehensive income. These freestanding derivatives are interest rate swaps, foreign currency swaps, credit default swaps (CDSs), foreign currency forwards, foreign currency options, and, in prior year periods, options on interest rate swaps (or interest rate swaptions). Interest rate and foreign currency swaps are used within VIEs to hedge the risk arising from interest rate and currency exchange risk, while the CDSs are used to increase the yield and improve the diversification of the portfolio. Foreign currency forwards and options are used in hedging foreign exchange risk on U.S. dollar-denominated investments in Aflac Japan's portfolio. Foreign currency forwards and options are used to hedge certain portions of forecasted cash flows denominated in yen. Interest rate swaps are used to hedge the variability of interest cash flows associated with the Company's variable interest rate notes. Cross-currency interest rate swaps, also referred to as foreign currency swaps, are used to economically convert certain U.S. dollar-denominated note obligations into yen-denominated principal and interest obligations. Interest rate swaptions have been used from time to time to hedge interest rate risk for certain U.S. dollar-denominated available-for-sale securities. The Company does not use derivatives for trading purposes, nor does the Company engage in leveraged derivative transactions. From time to time, the Company purchases certain investments that contain an embedded derivative. The Company assesses whether this embedded derivative is clearly and closely related to the asset that serves as its host contract. If the Company deems that the embedded derivative's terms are not clearly and closely related to the host contract, and a separate instrument with the same terms would qualify as a derivative instrument, the derivative is separated from that contract, held at fair value, and reported with the host instrument in the consolidated balance sheet, with changes in fair value reported in earnings. If the Company has elected the fair value option, the embedded derivative is not bifurcated, and the entire investment is held at fair value with changes in fair value reported in earnings. See Note 5 for a discussion on how the Company determines the fair value of its derivatives. Accruals on derivatives are typically recorded in accrued investment income or within other liabilities in the consolidated balance sheets. To qualify for hedge accounting treatment, a derivative must be highly effective in mitigating the designated risk of the hedged item. At the inception of hedging relationships for which the Company elects to designate for hedge accounting treatment, the Company formally documents all relationships between hedging instruments and hedged items, as well as its risk-management objectives and strategies for undertaking each hedge transaction. The Company documents the designation of each hedge as either (i) a hedge of the variability of cash flows to be received or paid related to a recognized asset or liability or the hedge of a forecasted transaction ("cash flow hedge"); (ii) a hedge of the estimated fair value of a recognized asset or liability ("fair value hedge"); or (iii) a hedge of a net investment in a foreign operation. The documentation process includes linking derivatives and non-derivative financial instruments that are designated as hedges to specific assets or groups of assets or liabilities on the statement of financial position or to specific forecasted transactions and defining the effectiveness and ineffectiveness testing methods to be used. At the hedge's inception and on an ongoing quarterly basis, the Company also formally assesses whether the derivatives and non-derivative financial instruments used in hedging activities have been, and are expected to continue to be, highly effective in offsetting their designated risk. Hedge effectiveness is assessed using qualitative and quantitative methods. The assessment of hedge effectiveness determines the accounting treatment of noncash changes in fair value. For assessing hedge effectiveness of cash flow hedges, qualitative methods may include the comparison of critical terms of the derivative to the hedged item, and quantitative methods may include regression or other statistical analysis of changes in cash flows associated with the hedge relationship. Hedge ineffectiveness of the hedge relationships on the Company's VIE cash flow hedges is measured each reporting period using the “Hypothetical Derivative Method.” For derivative instruments that are designated and qualify as cash flow hedges, the effective portion of the gain or loss on the derivative is reported as a component of other comprehensive income (loss) and reclassified into earnings in the same period or periods during which the hedged transaction affects earnings. Gains and losses on the derivative representing hedge ineffectiveness are recognized in current earnings within derivative and other gains (losses). All components of each derivative's gain or loss are included in the assessment of hedge effectiveness. Periodic derivative net coupon settlements are recorded in the line item of the consolidated statements of earnings in which the cash flows of the hedged item are recorded. For assessing hedge effectiveness of fair value hedges, qualitative methods may include the comparison of critical terms of the derivative to the hedged item, and quantitative methods may include regression or other statistical analysis of changes in fair value associated with the hedge relationship. Hedge ineffectiveness of the hedge relationships is measured each reporting period using the dollar offset method. For derivative instruments that are designated and qualify as fair value hedges, changes in the estimated fair value of the derivative, including amounts measured as ineffectiveness, and changes in the estimated fair value of the hedged item related to the designated risk being hedged, are reported in current earnings within derivative and other gains (losses). When assessing the effectiveness of the Company's fair value hedges, the Company excludes the changes in fair value related to the difference between the spot and the forward rate on its foreign currency forwards and the time value of options. For the hedge of the Company's net investment in Aflac Japan, the Company has designated the majority of the Parent Company's yen-denominated liabilities (notes payable and yen-denominated loans) as non-derivative hedging instruments and has designated certain foreign currency forwards and options as derivative hedging instruments. The Company makes its net investment hedge designation at the beginning of each quarter. For assessing hedge effectiveness of net investment hedges, if the total of the designated Parent Company non-derivative and derivatives notional is equal to or less than its net investment in Aflac Japan, the hedge is deemed to be effective. If the hedge is effective, the related exchange effect on the yen-denominated liabilities is reported in the unrealized foreign currency component of other comprehensive income. For derivatives designated as net investment hedges, Aflac follows the forward-rate method. According to that method, all changes in fair value, including changes related to the forward-rate component of foreign currency forward contracts and the time value of foreign currency options, are reported in the unrealized foreign currency component of other comprehensive income. Should these designated net investment hedge positions exceed the Company's net investment in Aflac Japan, the foreign exchange effect on the portion that exceeds its investment in Aflac Japan would be recognized in current earnings within derivative and other gains (losses). The Company discontinues hedge accounting prospectively when (1) it is determined that the derivative is no longer highly effective in offsetting changes in the estimated cash flows or fair value of a hedged item; (2) the derivative is de-designated as a hedging instrument; or (3) the derivative expires or is sold, terminated or exercised. When hedge accounting is discontinued on a cash flow hedge or fair value hedge, the derivative is carried in the consolidated balance sheets at its estimated fair value, with changes in estimated fair value recognized in current period earnings. For discontinued cash flow hedges, including those where the derivative is sold, terminated or exercised, amounts previously deferred in other comprehensive income (loss) are reclassified into earnings when earnings are impacted by the cash flow of the hedged item. If a derivative is not designated as an accounting hedge or its use in managing risk does not qualify for hedge accounting, changes in the estimated fair value of the derivative are generally reported within derivative and other gains (losses), which is a component of realized investment gains (losses). The fluctuations in estimated fair value of derivatives that have not been designated for hedge accounting can result in volatility in net earnings. The Company receives and pledges cash or other securities as collateral on open derivative positions. Cash received as collateral is reported as an asset with a corresponding liability for the return of the collateral. Cash pledged as collateral is recorded as a reduction to cash, and a corresponding receivable is recognized for the return of the cash collateral. The Company generally can repledge or resell collateral obtained from counterparties, although the Company does not typically exercise such rights. Securities received as collateral are not recognized unless the Company was to exercise its right to sell that collateral or exercise remedies on that collateral upon a counterparty default. Securities that the Company has pledged as collateral continue to be carried as investment assets on its balance sheet.
Deferred Policy Acquisition Costs	Deferred Policy Acquisition Costs: Certain direct and incremental costs of acquiring new business are deferred and amortized with interest over the premium payment periods in proportion to the ratio of annual premium income to total anticipated premium income. Anticipated premium income is estimated by using the same mortality, persistency and interest assumptions used in computing liabilities for future policy benefits. In this manner, the related acquisition expenses are matched with revenues. Deferred costs include the excess of current-year commissions over ultimate renewal-year commissions and certain incremental direct policy issue, underwriting and sales expenses. All of these incremental costs are directly related to successful policy acquisition. For some products, policyholders can elect to modify product benefits, features, rights or coverages by exchanging a contract for a new contract or by amendment, endorsement, or rider to a contract, or by the election of a feature or coverage within a contract. These transactions are known as internal replacements. The Company performs a two-stage analysis of the internal replacements to determine if the modification is substantive to the base policy. The stages of evaluation are as follows: 1) determine if the modification is integrated with the base policy, and 2) if it is integrated, determine if the resulting contract is substantially changed. For internal replacement transactions where the resulting contract is substantially unchanged, the policy is accounted for as a continuation of the replaced contract. Unamortized deferred acquisition costs from the original policy continue to be amortized over the expected life of the new policy, and the costs of replacing the policy are accounted for as policy maintenance costs and expensed as incurred. Examples include conversions of same age bands, certain family coverage changes, pricing era changes (decrease), and ordinary life becomes reduced paid-up and certain reinstatements. An internal replacement transaction that results in a policy that is substantially changed is accounted for as an extinguishment of the original policy and the issuance of a new policy. Unamortized deferred acquisition costs on the original policy are immediately expensed, and the costs of acquiring the new policy are capitalized and amortized in accordance with the Company's accounting policies for deferred acquisition costs. Further, the policy reserves are evaluated based on the new policy features, and any change (up or down) necessary is recognized at the date of contract change/modification. Examples include conversions-higher age bands, certain family coverage changes, pricing era changes (increase), lapse & re-issue, certain reinstatements and certain contract conversions. Riders can be considered internal replacements that are either integrated or non-integrated resulting in either substantially changed or substantially unchanged treatment. Riders are evaluated based on the specific facts and circumstances of the rider and are considered an expansion of the existing benefits with additional premium required. Non-integrated riders to existing contracts do not change the Company's profit expectations for the related products and are treated as a new policy establishment for incremental coverage. The Company measures the recoverability of DAC and the adequacy of its policy reserves annually by performing gross premium valuations on its business. (See the following discussion for further information regarding policy reserves.)
Policy Liabilities - Future Policy Benefits	Policy Liabilities:  Future policy benefits represent claims that are expected to occur in the future and are computed by a net level premium method using estimated future investment yields, persistency and recognized morbidity and mortality tables modified to reflect the Company's experience, including a provision for adverse deviation. These assumptions are generally established and considered locked at policy inception. These assumptions may only be unlocked in certain circumstances based on the results of periodic DAC recoverability and premium deficiency testing.
Policy Liabilities - Unpaid Policy Claims	Unpaid policy claims are estimates computed on an undiscounted basis using statistical analyses of historical claims experience adjusted for current trends and changed conditions. The ultimate liability may vary significantly from such estimates. The Company regularly adjusts these estimates as new claims experience emerges and reflects the changes in operating results in the year such adjustments are made.
Other Policy Liabilities	Other policy liabilities consist primarily of discounted advance premiums on deposit from policyholders in conjunction with their purchase of certain Aflac Japan limited-pay insurance products. These advanced premiums are deferred upon collection and recognized as premium revenue over the contractual premium payment period.
Internal Replacements of Insurance Contracts	For internal replacements that are determined to not be substantially unchanged, policy liabilities related to the original policy that was replaced are immediately released, and policy liabilities are established for the new insurance contract; however, for internal replacements that are considered substantially unchanged, no changes to the reserves are recognized.
Reinsurance Accounting Policy	Reinsurance: The Company enters into reinsurance agreements with other companies in the normal course of business. For each reinsurance agreement, the Company determines if the agreement provides indemnification against loss or liability relating to insurance risk in accordance with applicable accounting standards. Reinsurance premiums and benefits paid or provided are accounted for on bases consistent with those used in accounting for the original policies issued and the terms of the reinsurance contracts. Premiums, benefits and DAC are reported net of insurance ceded.
Income Taxes	Income Taxes: Income tax provisions are generally based on pretax earnings reported for financial statement purposes, which differ from those amounts used in preparing the Company's income tax returns. Deferred income taxes are recognized for temporary differences between the financial reporting basis and income tax basis of assets and liabilities, based on enacted tax laws and statutory tax rates applicable to the periods in which the Company expects the temporary differences to reverse. The Company records deferred tax assets for tax positions taken based on its assessment of whether the tax position is more likely than not to be sustained upon examination by taxing authorities. A valuation allowance is established for deferred tax assets when it is more likely than not that an amount will not be realized.
Policyholder Protection Corporation and State Guaranty Association Assessments	Policyholder Protection Corporation and State Guaranty Association Assessments: In Japan, the government has required the insurance industry to contribute to a policyholder protection corporation. The Company recognizes a charge for its estimated share of the industry's obligation once it is determinable. The Company reviews the estimated liability for policyholder protection corporation contributions on an annual basis and reports any adjustments in Aflac Japan's expenses. In the United States, each state has a guaranty association that supports insolvent insurers operating in those states. See Note 15 of the Notes to the Consolidated Financial Statements for further discussion of the guaranty fund assessments charged to the Company.
Treasury Stock	Treasury Stock: Treasury stock is reflected as a reduction of shareholders' equity at cost. The Company uses the weighted-average purchase cost to determine the cost of treasury stock that is reissued. The Company includes any gains and losses in additional paid-in capital when treasury stock is reissued.
Share-Based Compensation	Share-Based Compensation: The Company measures compensation cost related to its share-based payment transactions at fair value on the grant date, and the Company recognizes those costs in the financial statements over the vesting period during which the employee provides service in exchange for the award. The Company has formalized its entity-wide accounting policy election to estimate the number of awards that are expected to vest and the corresponding forfeitures.
Earnings Per Share	Earnings Per Share: The Company computes basic earnings per share (EPS) by dividing net earnings by the weighted-average number of unrestricted shares outstanding for the period. Diluted EPS is computed by dividing net earnings by the weighted-average number of shares outstanding for the period plus the shares representing the dilutive effect of share-based awards.
Reclassifications	Reclassifications: Certain reclassifications have been made to prior-year amounts to conform to current-year reporting classifications. These reclassifications had no impact on net earnings or total shareholders' equity. Prior year foreign currency transaction gains and losses have been reclassified from Other income (loss) to Realized investment gains (losses) - Derivative and other gains (losses) to conform to current-year reporting classifications. These reclassifications had no impact on net earnings or total shareholders' equity. This change in classification was made to reflect that the major source of the Company's foreign currency transaction gains and losses is directly or indirectly a result of its investment activity.
Recently Adopted Accounting Pronouncements	New Accounting Pronouncements Recently Adopted Accounting Pronouncements Consolidation - Interests Held through Related Parties That Are under Common Control: In October 2016, the FASB issued amendments which clarify the consolidation guidance on how a reporting entity that is the single decision maker of a variable interest entity (VIE) should treat indirect interests in the entity held through related parties that are under common control with the reporting entity when determining whether it is the primary beneficiary of that VIE. The Company adopted this guidance as of January 1, 2017. The adoption of this guidance did not have a significant impact on the Company's financial position, results of operations, or disclosures. Compensation - Stock Compensation - Improvements to Employee Share-Based Payment Accounting: In March 2016, the FASB issued amendments which simplify several aspects for share-based payment award transactions, including income tax consequences, classification of awards as either liability or equity, and classification on the statement of cash flows. The amendment requires prospective recognition of excess tax benefits and deficiencies in the income statement, rather than in paid-in capital. As a result of applying this requirement, the Company believes that recognition of excess tax benefits will increase volatility in its statement of operations, but the adoption of this guidance did not have a significant impact on the Company's financial position, results of operations, or disclosures. The amendment also requires all excess tax benefits and tax deficiencies (including tax benefits of dividends on share-based payment awards) to be recognized as income tax expense or benefit in the income statement. The guidance requires modified retrospective transition for settlements on all outstanding awards (both historical and future) that did not give rise to an excess benefit to be recorded through retained earnings on a cumulative-effect basis. The adoption of these amendments in the guidance did not have a significant impact on the Company's financial position, results of operations, or disclosures. Additionally, the amendment requires that the minimum statutory tax withholding for all outstanding liability awards be reclassified at the date of adoption to equity (assuming equity classification results from the guidance change), and as a cumulative-effect adjustment to equity on a modified retrospective basis. The adoption of these amendments in the guidance did not have a significant impact on the Company's financial position, results of operations, or disclosures. The guidance requires certain reclassifications of balances on the statement of cash flows to or from operating and financing activities. The reclassification guidance did not have a significant impact on the Company's statement of cash flows. The amendment allows an entity to elect whether to use estimates of forfeitures, or to account for forfeitures as they occur, using modified retrospective application. The Company adopted this guidance as of January 1, 2017. The Company made an entity-wide accounting policy election to estimate the number of awards that are expected to vest (consistent with the Company's prior policy) . The election and adoption of this guidance did not have a significant impact on the Company's financial position, results of operations, or disclosures. Investments - Equity Method and Joint Ventures - Simplifying the Transition to the Equity Method of Accounting: In March 2016, the FASB issued amendments which eliminate the requirement that when an investment qualifies for use of the equity method as a result of an increase in the level of ownership interest or degree of influence, an investor must adjust the investment, results of operations, and retained earnings retroactively on a step-by-step basis as if the equity method had been in effect during all previous periods that the investment had been held. Per the amendments, upon qualifying for the equity method of accounting, no retroactive adjustment of the investment is required. The amendments also require that an entity that has an available-for-sale equity security that becomes qualified for the equity method of accounting recognize through earnings the unrealized holding gain or loss in accumulated other comprehensive income at the date the investment becomes qualified for use of the equity method. The Company adopted this guidance as of January 1, 2017. The adoption of this guidance did not have a significant impact on the Company's financial position, results of operations, or disclosures. Derivatives and Hedging - Contingent Put and Call Options in Debt Instruments: In March 2016, the FASB issued amendments which clarify what steps are required when assessing whether the economic characteristics and risks of call (put) options are clearly and closely related to the economic characteristics and risks of their debt hosts, which is one of the criteria for bifurcating an embedded derivative. Consequently, when a call (put) option is contingently exercisable, an entity does not have to assess whether the event that triggers the ability to exercise a call (put) option is related to interest rates or credit risks. The Company adopted this guidance as of January 1, 2017. The adoption of this guidance did not have a significant impact on the Company's financial position, results of operations, or disclosures. Derivatives and Hedging - Effect of Derivative Contract Novations on Existing Hedge Accounting Relationships: In March 2016, the FASB issued amendments which clarify that a change in the counterparty to a derivative instrument that has been designated as the hedging instrument does not, in and of itself, require dedesignation of that hedging relationship provided that all other hedge accounting criteria remain intact. The Company adopted this guidance as of January 1, 2017. The adoption of this guidance did not have a significant impact on the Company's financial position, results of operations, or disclosures. Business Combinations - Simplifying the Accounting for Measurement-Period Adjustments: In September 2015, the FASB issued guidance requiring that an acquirer recognize adjustments to estimated amounts that are identified during the measurement period in the reporting period in which the adjustments are determined. In the same period’s financial statements, the acquirer is required to record income effects of the adjustments as if the accounting had been completed at the acquisition date. The acquirer is also required to present separately on the face of the income statement or disclose in the notes the portion of the amount recorded in current-period earnings by line item that would have been recorded in previous reporting periods if the adjustment to the estimated amounts had been recognized as of the acquisition date. The Company adopted this guidance as of January 1, 2016. The adoption of this guidance did not have a significant impact on the Company's financial position, results of operations, or disclosures. Financial Services - Insurance - Disclosures about Short-Duration Contracts: In May 2015, the FASB issued updated guidance requiring enhanced disclosures by all insurance entities that issue short-duration contracts. The amendments require insurance entities to disclose for annual reporting periods information about the liability for unpaid claims and claim adjustment expenses. The amendments also require insurance entities to disclose information about significant changes in methodologies and assumptions used to calculate the liability for unpaid claims and claim adjustment expenses. In addition, the amendments require insurance entities to disclose for annual and interim reporting periods a roll-forward of the liability for unpaid claims and claim adjustment expenses. For health insurance claims, the amendments require the disclosure of the total of incurred-but-not-reported liabilities and expected development on reported claims included in the liability for unpaid claims and claim adjustment expenses. The Company adopted this guidance as of December 31, 2016. The adoption of this guidance did not have a significant impact on the Company's disclosures. Fair Value Measurement - Disclosures for Investments in Certain Entities That Calculate Net Asset Value per Share (or Its Equivalent): In May 2015, the FASB issued updated guidance that removes the requirement to categorize within the fair value hierarchy all investments for which fair value is measured using the net asset value per share practical expedient. The amendments also remove the requirement to make certain disclosures for all investments that are eligible to be measured at fair value using the net asset value per share practical expedient. Rather, those disclosures are limited to investments for which the entity has elected to measure the fair value using that practical expedient. The Company adopted this guidance as of January 1, 2016. The adoption of this guidance did not have a significant impact on the Company's disclosures. Interest - Imputation of Interest - Simplifying the Presentation of Debt Issuance Costs: In April 2015, the FASB issued updated guidance to simplify presentation of debt issuance costs. The updated guidance requires that debt issuance costs related to a recognized debt liability be presented in the balance sheet as a direct deduction from the carrying amount of that debt liability, consistent with debt discounts. The recognition and measurement guidance for debt issuance costs are not affected by this amendment. In August 2015, the FASB issued updated Securities and Exchange Commission (SEC) Staff guidance pertaining to the presentation of debt issuance costs related to line-of-credit arrangements. The guidance states that an entity may defer and present debt issuance costs as an asset, subsequently amortizing the deferred debt issuance costs ratably over the term of the line-of-credit arrangement, regardless of whether there are any outstanding borrowings on the line-of-credit arrangement. The Company retrospectively adopted this guidance as of January 1, 2016. The retrospective adoption of this accounting standard resulted in a $40 million reduction to notes payable and other assets as of December 31, 2015, the earliest balance sheet date presented in the period of adoption, but did not have a significant impact on the Company's financial position, results of operations, or disclosures. Consolidation - Amendments to the Consolidation Analysis: In February 2015, the FASB issued updated guidance that affects evaluation of whether limited partnerships and similar legal entities (limited liability corporations and securitization structures, etc.) are VIEs, evaluation of whether fees paid to a decision maker or a service provider are a variable interest, and evaluation of the effect of fee arrangements and the effect of related parties on the determination of the primary beneficiary under the VIE model for consolidation. The updated guidance eliminates the presumption that a general partner should consolidate a limited partnership. Limited partnership and similar legal entities that provide partners with either substantive kick-out rights or substantive participating rights over the general partner will now be evaluated under the voting interest model rather than the VIE model for consolidation. In situations where no single party has a controlling financial interest in a VIE, the related party relationships under common control should be considered in their entirety in determining whether that common control group has a controlling financial interest in the VIE. The Company adopted this guidance as of January 1, 2016. The adoption of this guidance impacted the Company's footnote disclosures, but did not have a significant impact on its financial position or results of operations. Derivatives and Hedging - Determining Whether the Host Contract in a Hybrid Financial Instrument Issued in the Form of a Share Is More Akin to Debt or to Equity: In November 2014, the FASB issued guidance to clarify how to evaluate the economic characteristics and risks of a host contract in a hybrid financial instrument that is issued in the form of a share. The guidance also clarifies that an entity should assess the substance of the relevant terms and features when considering how to weight those terms and features. The Company adopted this guidance as of January 1, 2016. The adoption of this guidance did not have a significant impact on the Company's financial position, results of operations, or disclosures. Presentation of Financial Statements - Going Concern - Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern: In August 2014, the FASB issued this amendment that provides U.S. GAAP guidance on management’s responsibility in evaluating whether there is substantial doubt about a company’s ability to continue as a going concern and about related footnote disclosures. For each reporting period, management will be required to evaluate whether there are conditions or events that raise substantial doubt about a company’s ability to continue as a going concern within one year from the date the financial statements are issued. The new guidance requires a formal assessment of going concern by management based on criteria prescribed in the new guidance. The Company adopted this guidance as of December 31, 2016. The adoption of this guidance did not have a significant impact on the Company's financial position, results of operations, or disclosures, and no substantial doubt currently exists about the Company’s ability to continue as a going concern. Compensation - Stock Compensation - Accounting for Share-Based Payments When the Terms of an Award Provide That a Performance Target Could Be Achieved after the Requisite Service Period: In June 2014, the FASB issued this amendment that provides guidance on certain share-based payment awards that require a specific performance target that affects vesting and that could be achieved after the requisite service period be treated as a performance condition. A reporting entity should apply existing guidance to awards with performance conditions that affect vesting to account for such awards. Compensation cost should be recognized in the period in which it becomes probable that the performance target will be achieved and should represent the compensation cost attributable to the period(s) for which the requisite service has already been rendered. The total amount of compensation cost recognized during and after the requisite service period should reflect the number of awards that are expected to vest and should be adjusted to reflect those awards that ultimately vest. The Company adopted this guidance as of January 1, 2016. The adoption of this guidance did not have a significant impact on the Company's financial position, results of operations, or disclosures. Income Statement - Extraordinary and Unusual Items - Simplifying Income Statement Presentation by Eliminating the Concept of Extraordinary Items: In January 2015, the FASB issued updated guidance that eliminates from U.S. GAAP the concept of extraordinary items. Presentation and disclosure guidance for items that are unusual in nature or occur infrequently will be retained. The Company adopted this guidance as of January 1, 2015. The adoption of this guidance did not have a significant impact on the Company's financial position, results of operations, or disclosures. Receivables - Troubled Debt Restructurings by Creditors - Classification of Certain Government-Guaranteed Mortgage Loans upon Foreclosure: In August 2014, the FASB issued updated guidance for troubled debt restructurings affecting creditors that hold government guaranteed mortgage loans. The guidance requires that a mortgage loan be derecognized and a separate other receivable be recognized upon foreclosure if certain conditions are met. The Company adopted the guidance as of January 1, 2015. The adoption of this guidance did not have a significant impact on the Company’s financial position, results of operations, or disclosures. Transfers and Servicing - Repurchase-to-Maturity Transactions, Repurchase Financings, and Disclosures: In June 2014, the FASB issued updated guidance for repurchase agreement and security lending transactions to change the accounting for repurchase-to-maturity transactions and linked repurchase financings to be accounted for as secured borrowings, consistent with the accounting for other repurchase agreements. The amendments also require new disclosures to increase transparency about the types of collateral pledged in repurchase agreements and similar transactions accounted for as secured borrowings. The Company adopted accounting changes for the new guidance as of January 1, 2015, and adopted the required disclosures as of April 1, 2015. The adoption of this guidance did not have a significant impact on the Company’s financial position, results of operations, or disclosures. Receivables - Troubled Debt Restructurings by Creditors - Reclassification of Residential Real Estate Collateralized Consumer Mortgage Loans upon Foreclosure: In January 2014, the FASB issued updated guidance for troubled debt restructurings clarifying when an in substance repossession or foreclosure occurs, and when a creditor is considered to have received physical possession of residential real estate property collateralizing a consumer mortgage loan. The Company adopted the guidance as of January 1, 2015. The adoption of this guidance did not have a significant impact on the Company’s financial position, results of operations, or disclosures.
Description of Accounting Pronouncements Pending Adoption	Accounting Pronouncements Pending Adoption Income Statement - Reporting Comprehensive Income - Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income: In February 2018, the FASB issued amendments which allow a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the Tax Cuts and Jobs Act. The amendments eliminate the stranded tax effects resulting from the Tax Cuts and Jobs Act and also require certain disclosures about stranded tax effects. The amendments are effective for all entities for fiscal years beginning after December 15, 2018, and interim periods within those fiscal years. Public business entities may early adopt this guidance in any interim reporting period for which financial statements have not yet been issued. The amendments should be applied either in the period of adoption or retrospectively to each period (or periods) in which the effect of the change in the U.S. federal corporate income tax rate in the Tax Cuts and Jobs Act is recognized. The Company expects adoption of this guidance will result in an increase to accumulated other comprehensive income and a decrease to retained earnings and also result in additional disclosures. Leases - Land Easement Practical Expedient for Transition to Topic 842: In January 2018, FASB issued guidance which provides an entity with the option to elect a transition practical expedient to not evaluate, under Topic 842, land easements that exist or expired before the entity's adoption of Topic 842 and that were not previously accounted for as leases under Topic 840. The amendments clarify that new or modified land easements should be evaluated under the new leases standard once an entity has adopted the new standard. The amendments are effective for public business entities for fiscal years beginning after December 15, 2018, and interim periods within those fiscal years. Early adoption is permitted. The adoption of this guidance is not expected to have a significant impact on the Company's financial position, results of operations, or disclosures. Derivatives and Hedging - Targeted Improvements to Accounting for Hedging Activities: In August 2017, FASB issued guidance which improves and simplifies the accounting rules around hedge accounting and will create more transparency around how economic results are presented on financial statements. Issues addressed in this new guidance include: 1) risk component hedging, 2) accounting for the hedged item in fair value hedges of interest rate risk, 3) recognition and presentation of the effects of hedging instruments, and 4) amounts excluded from the assessment of hedge effectiveness. The amendments are effective for public business entities for fiscal years beginning after December 15, 2018, and interim periods within those fiscal years. Early adoption is permitted in any interim period after issuance of the guidance. The adoption of this guidance is not expected to have a significant impact on the Company's financial position, results of operations, or disclosures. Compensation-Stock Compensation: Scope of Modification Accounting: In May 2017, the FASB issued amendments to provide guidance clarifying when changes to the terms or conditions of a share-based payment award must be accounted for as modifications. An entity should apply modification accounting if the fair value, vesting conditions or classification of the award (as an equity instrument or liability instrument) changes as a result of the change in terms or conditions of the award. The amendments are effective for public business entities for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years. Early adoption is permitted and should be applied prospectively. The adoption of this guidance is not expected to have a significant impact on the Company's financial position, results of operations, or disclosures. Receivables-Nonrefundable Fees and Other Costs: Premium Amortization on Purchased Callable Debt Securities: In March 2017, the FASB issued amendments to shorten the amortization period for certain callable debt securities held at a premium. Specifically, the amendments require the premium to be amortized to the earliest call date. The amendments do not require an accounting change for securities held at a discount. The amendments are effective for public business entities for fiscal years beginning after December 15, 2018, and interim periods within those fiscal years. Early adoption is permitted, including adoption in an interim period. The adoption of this guidance is not expected to have a significant impact on the Company's financial position, results of operations, or disclosures. Compensation-Retirement Benefit: Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost: In March 2017, the FASB issued amendments requiring that an employer report the service cost component of net periodic pension cost and net periodic postretirement benefit cost in the same line item or items as other compensation costs arising from services rendered by the pertinent employees during the period. The other components of net periodic pension cost and net periodic postretirement benefit cost are required to be presented in the income statement separately from the service cost component and outside a subtotal of income from operations, if one is presented. If a separate line item or items are used to present the other components of net benefit cost, that line item or items must be appropriately described. If a separate line item or items are not used, the line item or items used in the income statement to present the other components of net benefit cost must be disclosed. The amendments in this update also allow only the service cost component to be eligible for capitalization when applicable. The amendments are effective for public business entities for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years. Early adoption is permitted. The adoption of this guidance is not expected to have a significant impact on the Company's financial position, results of operations, disclosures, or statements of cash flows. Other Income - Gains and Losses from the Derecognition of Nonfinancial Assets - Clarifying the Scope of Asset Derecognition Guidance and Accounting for Partial Sales of Nonfinancial Assets: In February 2017, the FASB issued amendments that clarify the scope and accounting guidance for the derecognition of a nonfinancial asset or a financial asset that meets the definition of an "in substance nonfinancial asset." The amendments define an "in substance nonfinancial asset" and provide additional accounting guidance for partial sales of nonfinancial assets. The amendments are effective for public business entities for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years. Earlier adoption is permitted for fiscal years beginning after December 15, 2016, including interim periods therein. An entity is required to apply the amendments at the same time that it applies the FASB amendments for Revenue from Contracts with Customers. The Company does not expect the adoption of this guidance to have a significant impact on its financial position, results of operations, disclosures, and statements of cash flows. Intangibles - Goodwill and Other - Simplifying the Test for Goodwill Impairment: In January 2017, the FASB issued amendments simplifying the subsequent measurement of goodwill. An entity, under this update, is no longer required to perform a hypothetical purchase price allocation to measure goodwill impairment. Instead, the entity should perform its annual or interim goodwill impairment test by comparing the fair value of a reporting unit with its carrying amount. The amendments are effective for public business entities that are SEC filers for annual or any interim goodwill impairment tests in fiscal years beginning after December 15, 2019. Early adoption is permitted for any goodwill impairment tests performed on testing dates after January 1, 2017. The Company does not expect the adoption of this guidance to have a significant impact on its financial position, results of operations, or disclosures. Business Combinations - Clarifying the Definition of a Business: In January 2017, the FASB issued amendments clarifying when a set of assets and activities is a business. The amendments provide a screen to exclude transactions where substantially all the fair value of the transferred set is concentrated in a single asset, or group of similar assets, from being evaluated as a business. The amendments are effective for public business entities beginning after December 15, 2017, including interim periods within those periods. The Company does not expect the adoption of this guidance to have a significant impact on its financial position, results of operations, or disclosures. Statement of Cash Flows - Restricted Cash: In November 2016, the FASB issued amendments requiring that a statement of cash flows explain the change during the period in the total of cash, cash equivalents, and amounts generally described as restricted cash or restricted cash equivalents. The amendments are effective for public business entities for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years. Early adoption is permitted. The Company does not expect the adoption of this guidance to have a significant impact on its financial position, results of operations, disclosures, or statement of cash flows. Income Taxes - Intra-Entity Transfers of Assets Other Than Inventory: In October 2016, the FASB issued amendments that require an entity to recognize the income tax consequences of an intra-entity transfer of an asset other than inventory when the transfer occurs. The amendments are effective for public business entities for annual reporting periods beginning after December 15, 2017, including interim reporting periods within those annual reporting periods. Early adoption is permitted. The Company does not expect the adoption of this guidance to have a significant impact on its financial position, results of operations, and disclosures. Statement of Cash Flows - Classification of Certain Cash Receipts and Cash Payment s: In August 2016, the FASB issued amendments that provide guidance on eight specific statement of cash flows classification issues. The amendments are effective for public companies for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years. Early adoption is permitted for any interim or annual period. The adoption of this guidance is not expected to have a significant impact on the Company's financial position, results of operations, disclosures, or statements of cash flows. Financial Instruments - Credit Losses - Measurement of Credit Losses on Financial Instruments: In June 2016, the FASB issued amendments that require a financial asset (or a group of financial assets) measured on an amortized cost basis to be presented net of an allowance for credit losses in order to reflect the amount expected to be collected on the financial asset(s). The measurement of expected credit losses is amended by replacing the incurred loss impairment methodology in current U.S. GAAP with a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to inform about a credit loss. Credit losses on available-for-sale debt securities will continue to be measured in a manner similar to current U.S. GAAP. However, the amendments require that credit losses be presented as an allowance rather than as a writedown. Other amendments include changes to the balance sheet presentation and interest income recognition of purchased financial assets with a more-than-insignificant amount of credit deterioration since origination. The amendments are effective for public companies for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. Companies may early adopt this guidance as of the fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. The Company has identified certain financial instruments in scope of this guidance to include certain fixed maturity securities, loans and loan receivables and reinsurance recoverables (See Notes 3 and 7 for current balances of instruments in scope). The Company is continuing its progress towards updating its credit loss projection models and accounting systems in order to comply with the required changes in measurement of credit losses. The Company currently expects loans and loan receivables and held-to-maturity fixed-maturity securities to be the asset classes most significantly impacted upon adoption of the guidance. The Company continues to evaluate the impact of adoption of this guidance on its financial position, results of operations, and disclosures. Leases: In February 2016, the FASB issued updated guidance for accounting for leases. Per the amendments, lessees will be required to recognize all leases on the balance sheet with the exception of short-term leases. A lease liability will be recorded for the obligation of a lessee to make lease payments arising from a lease. A right-of-use asset will be recorded which represents the lessee’s right to use, or to control the use of, a specified asset for a lease term. Under the new guidance, lessor accounting is largely unchanged. The amendments are effective for public companies for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. Early adoption is permitted, including adoption in an interim period. The Company has identified certain operating leases in scope of this guidance to include office space and equipment leases (See Note 15 of the Notes to the Consolidated Financial Statements in the 2016 Annual Report for current balances of leases in scope). The leases within scope of this guidance will increase the Company's right-of-use assets and lease liabilities recorded on its statement of financial position, however the Company estimates leases within scope of the guidance to represent less than 1% of its total assets as of December 31, 2017. The Company estimates that the adoption of this guidance will not have a significant impact on its financial position, results of operations, and disclosures. Financial Instruments - Overall - Recognition and Measurement of Financial Assets and Financial Liabilities: In January 2016, the FASB issued guidance to address certain aspects of recognition, measurement, presentation, and disclosure of financial instruments. The main provisions of this guidance require certain equity investments to be measured at fair value with changes in fair value recognized in net earnings; separate presentation in other comprehensive income for changes in fair value of financial liabilities measured under the fair value option that are due to instrument-specific credit risk; and changes in disclosures associated with the fair value of financial instruments. The guidance also clarifies that entities should evaluate the need for a valuation allowance on a deferred tax asset (DTA) related to available-for-sale (AFS) securities in combination with the entity's other DTAs. The amendments are effective for public companies for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. Early adoption is not permitted, with the exception of the own credit provision if an entity has elected to measure a liability at fair value. The Company has determined that the most significant impact of adopting this guidance will be the requirement to report changes in fair value in net earnings for all equity investments within scope of this guidance. The Company estimates the cumulative effect adjustment of adopting this guidance will increase beginning 2018 retained earnings and decrease beginning 2018 accumulated other comprehensive income by $133 million , net of taxes. The Company also expects that the adoption of this guidance may potentially increase volatility in its consolidated statements of earnings on a prospective basis. Revenue from Contracts with Customers: In May 2014, the FASB issued updated guidance that affects any entity that either enters into contracts with customers to transfer goods or services or enters into contracts for the transfer of nonfinancial assets unless those contracts are within the scope of other standards (e.g., insurance contracts or lease contracts). The core principle of the guidance is that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. In August 2015, the FASB deferred the effective date for this standard to annual reporting periods beginning after December 15, 2017, including interim periods within that reporting period. Earlier application is permitted only as of annual reporting periods beginning after December 15, 2016, including interim reporting periods. The Company has identified revenue in scope of this guidance to include certain revenues associated with affiliated entities in support of its operations. The Company estimates the revenue within scope of the guidance to represent significantly less than 1% of its total revenues for the year ended December 31, 2017, and adoption of this guidance will not have a significant impact on its financial position, results of operations, and disclosures.

BUSINESS SEGMENT AND FOREIGN 30

BUSINESS SEGMENT AND FOREIGN INFORMATION (Tables)	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Reconciliation of Revenue from Segments to Consolidated	Information regarding operations by segment for the years ended December 31 follows: (In millions) 2017 2016 2015 Revenues: Aflac Japan: Net earned premiums: Cancer $ 5,612 $ 5,639 $ 4,933 Medical and other health 3,379 3,429 3,092 Life insurance 3,761 4,469 4,021 Net investment income, less amortized hedge costs (1) 2,235 2,368 2,364 Other income 41 40 31 Total Aflac Japan 15,028 15,945 14,441 Aflac U.S.: Net earned premiums: Accident/disability 2,537 2,469 2,391 Cancer 1,308 1,299 1,293 Other health 1,445 1,415 1,395 Life insurance 273 271 268 Net investment income 721 703 678 Other income 5 10 8 Total Aflac U.S. 6,289 6,167 6,033 Other business segments 140 275 225 Total business segment revenues 21,457 22,387 20,699 Corporate and eliminations 210 85 79 Total operating revenues 21,667 22,472 20,778 Realized investment gains (losses) (1), (2), (3) 0 87 94 Total revenues $ 21,667 $ 22,559 $ 20,872 (1) Amortized hedge costs related to hedging U.S. dollar-denominated investments held in Aflac Japan were $228 , $186 and $72 for 2017, 2016 and 2015, respectively, and have been reclassified from realized investment gains (losses) and reported as a deduction from net investment income when analyzing segment operations to conform to current year reporting. (2) Excluding a gain of $77 in 2017 and $85 in both 2016 and 2015 related to the interest rate component of the change in fair value of foreign currency swaps on notes payable which is classified as an operating gain when analyzing segment operations (3) Prior year foreign currency transaction gains and losses have been reclassified from other non-operating income (loss) to realized investment gains (losses) to conform to current-year reporting classifications. These reclassifications had no impact on total revenues.
Reconciliation of Operating Profit (Loss) from Segments to Consolidated	(In millions) 2017 2016 2015 Pretax earnings: Aflac Japan (1) $ 3,054 $ 3,148 $ 3,103 Aflac U.S. 1,245 1,208 1,101 Other business segments 11 18 14 Total business segment pretax operating earnings 4,310 4,374 4,218 Interest expense, noninsurance operations (122 ) (128 ) (146 ) Corporate and eliminations (101 ) (129 ) (71 ) Pretax operating earnings 4,087 4,117 4,001 Realized investment gains (losses) (1), (2), (3) 0 87 94 Other non-operating income (loss) (3), (4) (69 ) (137 ) (233 ) Total earnings before income taxes $ 4,018 $ 4,067 $ 3,862 Income taxes applicable to pretax operating earnings $ 1,370 $ 1,426 $ 1,377 Effect of foreign currency translation on after-tax (41 ) 141 (198 ) (1) Amortized hedge costs related to hedging U.S. dollar-denominated investments held in Aflac Japan were $228 , $186 and $72 for 2017, 2016 and 2015 respectively, and have been reclassified from realized investment gains (losses) and reported as a deduction from pretax operating earnings when analyzing segment operations to conform to current year reporting. (2) Excluding a gain of $77 in 2017 and $85 in both 2016 and 2015 related to the interest rate component of the change in fair value of foreign currency swaps on notes payable which is classified as an operating gain when analyzing segment operations (3) Prior year foreign currency transaction gains and losses have been reclassified from other non-operating income (loss) to realized investment gains (losses) to conform to current-year reporting classifications. These reclassifications had no impact on total earnings before income taxes. (4) Includes expense of $13 in 2017, $137 in 2016 and $230 in 2015 for the early extinguishment of debt
Reconciliation of Assets from Segment to Consolidated	Assets as of December 31 were as follows: (In millions) 2017 2016 2015 Assets: Aflac Japan $ 114,402 $ 107,858 $ 97,646 Aflac U.S. 19,893 19,453 18,537 Other business segments 547 270 188 Total business segment assets 134,842 127,581 116,371 Corporate and eliminations 2,375 2,238 1,885 Total assets $ 137,217 $ 129,819 $ 118,256 Amounts prior to 2016 have been adjusted for the adoption of the accounting guidance on January 1, 2016 related to debt issuance costs
Foreign Currency Disclosure	Yen-Translation Effects:  The following table shows the yen/dollar exchange rates used for or during the periods ended December 31 . Exchange effects were calculated using the same yen/dollar exchange rate for the current year as for each respective prior year. 2017 2016 2015 Statements of Earnings: Weighted-average yen/dollar exchange rate 112.16 108.70 120.99 Yen percent strengthening (weakening) (3.1 )% 11.3 % (12.8 )% Exchange effect on pretax operating earnings (in millions) $ (63 ) $ 218 $ (288 ) 2017 2016 Balance Sheets: Yen/dollar exchange rate at December 31 113.00 116.49 Yen percent strengthening (weakening) 3.1 % 3.5 % Exchange effect on total assets (in millions) $ 2,593 $ 2,820 Exchange effect on total liabilities (in millions) 2,848 3,109
Schedule of Intercompany Transfers of Funds	Information on transfers for each of the years ended December 31 is shown below. See Note 13 for information concerning restrictions on transfers from Aflac Japan. (In millions) 2017 2016 2015 Management fees $ 93 $ 79 $ 53 Allocated expenses 109 106 101 Profit repatriation 1,150 1,286 2,139 Total transfers from Aflac Japan $ 1,352 $ 1,471 $ 2,293
Property, Plant and Equipment	Classes of property and equipment as of December 31 were as follows: (In millions) 2017 2016 Property and equipment: Land $ 168 $ 166 Buildings 441 421 Equipment and furniture 372 355 Total property and equipment 981 942 Less accumulated depreciation 547 509 Net property and equipment $ 434 $ 433

INVESTMENTS (Tables)

INVESTMENTS (Tables)	12 Months Ended
	Dec. 31, 2017
Schedule Of Net Investment Income	The components of net investment income for the years ended December 31 were as follows: (In millions) 2017 2016 2015 Fixed-maturity securities $ 3,094 $ 3,214 $ 3,094 Perpetual securities 79 94 114 Equity securities 42 35 3 Other investments 94 31 15 Short-term investments and cash equivalents 25 11 4 Gross investment income 3,334 3,385 3,230 Less investment expenses 114 107 95 Net investment income $ 3,220 $ 3,278 $ 3,135
Available-for-sale Securities	The amortized cost for the Company's investments in debt and perpetual securities, the cost for equity securities and the fair values of these investments at December 31 are shown in the following tables. 2017 (In millions) Cost or Gross Gross Fair Securities available for sale, carried at fair value: Fixed maturities: Yen-denominated: Japan government and agencies $ 27,980 $ 3,363 $ 271 $ 31,072 Municipalities 314 28 12 330 Mortgage- and asset-backed securities 242 29 0 271 Public utilities 1,635 352 6 1,981 Sovereign and supranational 1,380 190 1 1,569 Banks/financial institutions 3,521 524 26 4,019 Other corporate 3,890 771 7 4,654 Total yen-denominated 38,962 5,257 323 43,896 U.S. dollar-denominated: U.S. government and agencies 146 13 1 158 Municipalities 872 168 0 1,040 Mortgage- and asset-backed securities 161 12 0 173 Public utilities 5,116 884 27 5,973 Sovereign and supranational 267 73 0 340 Banks/financial institutions 2,762 604 8 3,358 Other corporate 25,384 2,620 418 27,586 Total U.S. dollar-denominated 34,708 4,374 454 38,628 Total fixed maturities 73,670 9,631 777 82,524 Perpetual securities: Yen-denominated: Banks/financial institutions 1,221 287 27 1,481 Other corporate 195 38 0 233 U.S. dollar-denominated: Banks/financial institutions 46 29 0 75 Total perpetual securities 1,462 354 27 1,789 Equity securities: Yen-denominated 561 135 1 695 U.S. dollar-denominated 285 45 2 328 Total equity securities 846 180 3 1,023 Total securities available for sale $ 75,978 $ 10,165 $ 807 $ 85,336 2016 (In millions) Cost or Gross Gross Fair Securities available for sale, carried at fair value: Fixed maturities: Yen-denominated: Japan government and agencies $ 22,857 $ 3,359 $ 160 $ 26,056 Municipalities 246 29 8 267 Mortgage- and asset-backed securities 1,096 33 8 1,121 Public utilities 1,533 318 3 1,848 Sovereign and supranational 862 186 5 1,043 Banks/financial institutions 2,673 403 74 3,002 Other corporate 3,192 623 3 3,812 Total yen-denominated 32,459 4,951 261 37,149 U.S dollar-denominated: U.S. government and agencies 148 10 0 158 Municipalities 894 142 8 1,028 Mortgage- and asset-backed securities 196 20 0 216 Public utilities 5,205 690 60 5,835 Sovereign and supranational 335 91 0 426 Banks/financial institutions 2,570 507 16 3,061 Other corporate 24,556 2,021 690 25,887 Total U.S. dollar-denominated 33,904 3,481 774 36,611 Total fixed maturities 66,363 8,432 1,035 73,760 Perpetual securities: Yen-denominated: Banks/financial institutions 1,266 128 49 1,345 Other corporate 189 24 0 213 U.S. dollar-denominated: Banks/financial institutions 51 24 0 75 Total perpetual securities 1,506 176 49 1,633 Equity securities: Yen-denominated 624 83 2 705 Dollar-denominated 579 31 6 604 Total equity securities 1,203 114 8 1,309 Total securities available for sale $ 69,072 $ 8,722 $ 1,092 $ 76,702
Held-to-maturity Securities	2016 (In millions) Cost or Gross Gross Fair Securities held to maturity, carried at amortized cost: Fixed maturities: Yen-denominated: Japan government and agencies $ 20,702 $ 5,338 $ 0 $ 26,040 Municipalities 350 107 0 457 Mortgage- and asset-backed securities 30 2 0 32 Public utilities 3,201 358 23 3,536 Sovereign and supranational 2,602 283 8 2,877 Banks/financial institutions 3,731 195 26 3,900 Other corporate 2,734 452 7 3,179 Total yen-denominated 33,350 6,735 64 40,021 Total securities held to maturity $ 33,350 $ 6,735 $ 64 $ 40,021 2017 (In millions) Cost or Gross Gross Fair Securities held to maturity, carried at amortized cost: Fixed maturities: Yen-denominated: Japan government and agencies $ 21,331 $ 5,160 $ 0 $ 26,491 Municipalities 357 105 0 462 Mortgage- and asset-backed securities 26 1 0 27 Public utilities 3,300 398 0 3,698 Sovereign and supranational 1,523 312 0 1,835 Banks/financial institutions 2,206 190 9 2,387 Other corporate 2,687 485 0 3,172 Total yen-denominated 31,430 6,651 9 38,072 Total securities held to maturity $ 31,430 $ 6,651 $ 9 $ 38,072
Investments Classified by Contractual Maturity Date	The contractual maturities of the Company's investments in fixed maturities at December 31, 2017 , were as follows: Aflac Japan Aflac U.S. (In millions) Amortized Fair Amortized Fair Available for sale: Due in one year or less $ 234 $ 243 $ 86 $ 89 Due after one year through five years 7,155 7,391 508 542 Due after five years through 10 years 7,812 8,385 2,726 2,946 Due after 10 years 45,028 51,269 8,482 9,927 Mortgage- and asset-backed securities 283 322 40 41 Total fixed maturities available for sale $ 60,512 $ 67,610 $ 11,842 $ 13,545 Held to maturity: Due in one year or less $ 885 $ 903 $ 0 $ 0 Due after one year through five years 434 455 0 0 Due after five years through 10 years 1,634 1,802 0 0 Due after 10 years 28,451 34,885 0 0 Mortgage- and asset-backed securities 26 27 0 0 Total fixed maturities held to maturity $ 31,430 $ 38,072 $ 0 $ 0
Economic Maturities of Investments in Perpetual Securities	The economic maturities of the Company's investments in perpetual securities, which were all reported as available for sale at December 31, 2017 , were as follows: Aflac Japan Aflac U.S. (In millions) Amortized Fair Amortized Fair Due after one year through five years $ 194 $ 233 $ 0 $ 0 Due after 10 years 1,229 1,495 39 61 Total perpetual securities available for sale $ 1,423 $ 1,728 $ 39 $ 61
Investment Exposures Exceeding 10 Percent Shareholders Equity	Investment exposures that individually exceeded 10% of shareholders' equity as of December 31 were as follows: 2017 2016 (In millions) Credit Amortized Fair Credit Amortized Fair Japan National Government (1) A $48,399 $56,532 A $42,931 $51,345 (1) Japan Government Bonds (JGBs) or JGB-backed securities
Gain (Loss) on Investments	Information regarding pretax realized gains and losses from investments for the years ended December 31 follows: (In millions) 2017 2016 2015 Realized investment gains (losses): Fixed maturities: Available for sale: Gross gains from sales $ 36 $ 77 $ 224 Gross losses from sales (82 ) (134 ) (8 ) Net gains (losses) from redemptions (23 ) 112 51 Other-than-temporary impairment losses (7 ) (24 ) (152 ) Total fixed maturities (76 ) 31 115 Perpetual securities: Available for sale: Net gains (losses) from redemptions 4 64 35 Other-than-temporary impairment losses 0 (2 ) 0 Total perpetual securities 4 62 35 Equity securities: Gross gains from sales 104 0 0 Gross losses from sales (11 ) 0 0 Net gains (losses) from redemptions 0 22 0 Other-than-temporary impairment losses (22 ) (57 ) (1 ) Total equity securities 71 (35 ) (1 ) Loan loss reserves (8 ) (2 ) (1 ) Derivatives and other: Derivative gains (losses) (109 ) (255 ) (10 ) Foreign currency gains (losses) (33 ) 185 (32 ) Total derivatives and other (142 ) (70 ) (42 ) Total realized investment gains (losses) $ (151 ) $ (14 ) $ 106
Unrealized Gain (Loss) on Investments	Information regarding changes in unrealized gains and losses from investments for the years ended December 31 follows: (In millions) 2017 2016 2015 Changes in unrealized gains (losses): Fixed maturities: Available for sale $ 1,457 $ 2,690 $ (2,481 ) Perpetual securities: Available for sale 200 21 (123 ) Equity securities 71 88 9 Total change in unrealized gains (losses) $ 1,728 $ 2,799 $ (2,595 )
Net Effect on Shareholders' Equity of Unrealized Gains and Losses from Investment Securities	The net effect on shareholders' equity of unrealized gains and losses from investment securities at December 31 was as follows: (In millions) 2017 2016 Unrealized gains (losses) on securities available for sale $ 9,358 $ 7,630 Deferred income taxes (1) (3,394 ) (2,825 ) Shareholders’ equity, unrealized gains (losses) on investment securities $ 5,964 $ 4,805 (1) See Note 10 for discussion of the accounting treatment of tax on amounts recorded in accumulated other comprehensive income pursuant to the Tax Act.
Investments Gross Unrealized Loss Aging	The following tables show the fair values and gross unrealized losses of the Company's available-for-sale and held-to-maturity investments that were in an unrealized loss position, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position at December 31 . 2017 Total Less than 12 months 12 months or longer (In millions) Fair Unrealized Fair Unrealized Fair Unrealized Fixed Maturities: U.S. government and U.S. dollar-denominated $ 74 $ 1 $ 74 $ 1 $ 0 $ 0 Japan government and Yen-denominated 5,255 271 1,264 9 3,991 262 Municipalities: Yen-denominated 129 12 10 0 119 12 Public utilities: U.S. dollar-denominated 785 27 221 3 564 24 Yen-denominated 83 6 0 0 83 6 Sovereign and supranational: Yen-denominated 309 1 309 1 0 0 Banks/financial institutions: U.S. dollar-denominated 362 8 316 5 46 3 Yen-denominated 1,162 35 394 4 768 31 Other corporate: U.S. dollar-denominated 7,741 418 2,839 50 4,902 368 Yen-denominated 440 7 349 4 91 3 Total fixed maturities 16,340 786 5,776 77 10,564 709 Perpetual securities: Yen-denominated 345 27 0 0 345 27 Total perpetual securities 345 27 0 0 345 27 Equity securities: U.S. dollar-denominated 41 2 21 0 20 2 Yen-denominated 40 1 39 1 1 0 Total equity securities 81 3 60 1 21 2 Total $ 16,766 $ 816 $ 5,836 $ 78 $ 10,930 $ 738 2016 Total Less than 12 months 12 months or longer (In millions) Fair Unrealized Fair Unrealized Fair Unrealized Fixed Maturities: Japan government and Yen-denominated $ 3,958 $ 160 $ 3,958 $ 160 $ 0 $ 0 Municipalities: U.S. dollar-denominated 44 8 0 0 44 8 Yen-denominated 105 8 105 8 0 0 Mortgage- and asset- Yen-denominated 713 8 713 8 0 0 Public utilities: U.S. dollar-denominated 1,265 60 790 32 475 28 Yen-denominated 635 26 347 14 288 12 Sovereign and supranational: Yen-denominated 244 13 38 5 206 8 Banks/financial institutions: U.S. dollar-denominated 268 16 238 10 30 6 Yen-denominated 1,521 100 636 19 885 81 Other corporate: U.S. dollar-denominated 10,462 690 7,252 346 3,210 344 Yen-denominated 321 10 321 10 0 0 Total fixed maturities 19,536 1,099 14,398 612 5,138 487 Perpetual securities: Yen-denominated 479 49 85 1 394 48 Total perpetual securities 479 49 85 1 394 48 Equity securities: U.S. dollar-denominated 211 6 211 6 0 0 Yen-denominated 49 2 49 2 0 0 Total equity securities 260 8 260 8 0 0 Total $ 20,275 $ 1,156 $ 14,743 $ 621 $ 5,532 $ 535
Other Investments	Other Investments The table below reflects the composition of the carrying value for other investments as of December 31. (In millions) 2017 2016 Other investments: Transitional real estate loans $ 1,235 $ 0 Commercial mortgage loans 908 855 Middle market loans 859 319 Policy loans 210 184 Short-term investments 57 89 Other 133 3 Total other investments $ 3,402 $ 1,450
Securities Lending Transactions Accounted for as Secured Borrowings	Details of our securities lending activities as of December 31 were as follows: Securities Lending Transactions Accounted for as Secured Borrowings 2017 Remaining Contractual Maturity of the Agreements (In millions) Overnight (1) Up to 30 Total Securities lending transactions: Japan government and agencies $ 0 $ 49 $ 49 Public utilities 73 0 73 Banks/financial institutions 54 0 54 Other corporate 415 0 415 Equity securities 15 0 15 Total borrowings $ 557 $ 49 $ 606 Gross amount of recognized liabilities for securities lending transactions $ 606 Amounts related to agreements not included in offsetting disclosure in Note 4 $ 0 (1) These securities are pledged as collateral under the Company's U.S. securities lending program and can be called at its discretion; therefore, they are classified as Overnight and Continuous. Securities Lending Transactions Accounted for as Secured Borrowings 2016 Remaining Contractual Maturity of the Agreements (In millions) Overnight (1) Up to 30 Total Securities lending transactions: Public utilities $ 62 $ 0 $ 62 Banks/financial institutions 34 0 34 Other corporate 430 0 430 Total borrowings $ 526 $ 0 $ 526 Gross amount of recognized liabilities for securities lending transactions $ 526 Amounts related to agreements not included in offsetting disclosure in Note 4 $ 0 (1) These securities are pledged as collateral under the Company's U.S. securities lending program and can be called at its discretion; therefore, they are classified as Overnight and Continuous.
Variable Interest Entity, Consolidated
Investments in Variable Interest Entities	The following table presents the cost or amortized cost, fair value and balance sheet caption in which the assets and liabilities of consolidated VIEs are reported as of December 31. Investments in Consolidated Variable Interest Entities 2017 2016 (In millions) Cost or Amortized Fair Cost or Amortized Fair Assets: Fixed maturities, available for sale $ 4,300 $ 5,294 $ 4,168 $ 4,982 Perpetual securities, available for sale 238 215 237 208 Equity securities 606 753 972 1,044 Other investments (1) 2,341 2,328 819 789 Other assets (2) 151 151 127 127 Total assets of consolidated VIEs $ 7,636 $ 8,741 $ 6,323 $ 7,150 Liabilities: Other liabilities (2) $ 128 $ 128 $ 146 $ 146 Total liabilities of consolidated VIEs $ 128 $ 128 $ 146 $ 146
Variable Interest Entity, Not Consolidated
Investments in Variable Interest Entities	The table below reflects the amortized cost, fair value and balance sheet caption in which the Company's investment in VIEs not consolidated are reported as of December 31. Investments in Variable Interest Entities Not Consolidated 2017 2016 (In millions) Amortized Fair Amortized Fair Assets: Fixed maturities, available for sale $ 4,827 $ 5,506 $ 4,729 $ 5,261 Perpetual securities, available for sale 177 218 172 200 Fixed maturities, held to maturity 2,549 2,929 2,563 2,948 Other investments 55 55 1 1 Total investments in VIEs not consolidated $ 7,608 $ 8,708 $ 7,465 $ 8,410

DERIVATIVE INSTRUMENTS (Tables)

DERIVATIVE INSTRUMENTS (Tables)	12 Months Ended
	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Derivative Instruments in Statement of Financial Position, Fair Value	2017 2016 (In millions) Asset Liability Asset Liability Hedge Designation/ Derivative Notional Fair Value Fair Value Notional Fair Value Fair Value Cash flow hedges: Foreign currency swaps $ 75 $ 0 $ (8 ) $ 75 $ 0 $ (10 ) Total cash flow hedges 75 0 (8 ) 75 0 (10 ) Fair value hedges: Foreign currency forwards 7,640 2 (221 ) 10,965 0 (759 ) Foreign currency options 7,670 0 (2 ) 4,224 2 (32 ) Total fair value hedges 15,310 2 (223 ) 15,189 2 (791 ) Net investment hedge: Foreign currency forwards 5 0 0 209 5 (2 ) Foreign currency options 434 12 (1 ) 843 41 (17 ) Total net investment hedge 439 12 (1 ) 1,052 46 (19 ) Non-qualifying strategies: Foreign currency swaps 5,386 296 (189 ) 6,266 490 (220 ) Foreign currency forwards 3,683 20 (53 ) 21,218 667 (956 ) Foreign currency options 770 0 0 41 0 (2 ) Credit default swaps 88 1 0 86 2 0 Total non-qualifying strategies 9,927 317 (242 ) 27,611 1,159 (1,178 ) Total derivatives $ 25,751 $ 331 $ (474 ) $ 43,927 $ 1,207 $ (1,998 ) Balance Sheet Location Other assets $ 10,948 $ 331 $ 0 $ 18,329 $ 1,207 $ 0 Other liabilities 14,803 0 (474 ) 25,598 0 (1,998 ) Total derivatives $ 25,751 $ 331 $ (474 ) $ 43,927 $ 1,207 $ (1,998 )
Schedule of Fair Value Hedging Instruments, Statements of Financial Performance and Financial Position, Location	The following table presents the gains and losses on derivatives and the related hedged items in fair value hedges for the years ended December 31. Fair Value Hedging Relationships (In millions) Hedging Derivatives Hedged Items Hedging Derivatives Hedged Items Total Gains (Losses) Gains (Losses) Gains (Losses) Ineffectiveness 2017: Foreign currency Fixed-maturity and equity securities $ 98 $ (202 ) $ 300 $ (278 ) $ 22 Foreign currency Fixed-maturity securities 21 10 11 (10 ) 1 2016: Foreign currency forwards Fixed-maturity and equity securities $ 207 $ (338 ) $ 545 $ (566 ) $ (21 ) Foreign currency options Fixed-maturity securities (95 ) (18 ) (77 ) 70 (7 ) 2015: Foreign currency forwards Fixed-maturity securities $ (133 ) $ (136 ) $ 3 $ (5 ) $ (2 ) Foreign currency options Fixed-maturity securities (4 ) 3 (7 ) 7 0 Interest rate Fixed-maturity securities (95 ) 19 (114 ) 99 (15 )
Schedule of Derivative Instruments, Gain (Loss) in Statement of Financial Performance	The following table summarizes the impact to realized investment gains (losses) and other comprehensive income (loss) from all derivatives and hedging instruments for the years ended December 31. 2017 2016 2015 (In millions) Realized Investment Other (1) Realized Investment Other (1) Realized Other (1) Qualifying hedges: Cash flow hedges: Foreign currency swaps $ 0 $ 1 $ 1 $ 3 $ 0 $ 0 Total cash flow hedges 0 1 1 3 0 0 Fair value hedges: Foreign currency forwards (2) (180 ) 0 (359 ) 0 (138 ) 0 Foreign currency options ( 2) 11 0 (25 ) 0 3 0 Interest rate swaptions (2) 0 0 0 0 4 0 Total fair value hedges (169 ) 0 (384 ) 0 (131 ) 0 Net investment hedge: Non-derivative hedging 0 (15 ) 0 0 0 3 Foreign currency forwards 0 (25 ) 0 (118 ) 0 4 Foreign currency options 0 5 0 73 0 0 Total net investment hedge 0 (35 ) 0 (45 ) 0 7 Non-qualifying strategies: Foreign currency swaps 53 0 117 0 16 0 Foreign currency forwards 8 0 9 0 100 0 Credit default swaps (1 ) 0 2 0 1 0 Interest rate swaps 0 0 0 0 5 0 Futures 0 0 0 0 (1 ) 0 Total non- qualifying strategies 60 0 128 0 121 0 Total $ (109 ) $ (34 ) $ (255 ) $ (42 ) $ (10 ) $ 7 (1) Cash flow hedge items are recorded as unrealized gains (losses) on derivatives and net investment hedge items are recorded in the unrealized foreign currency translation gains (losses) line in the consolidated statement of comprehensive income (loss). (2) Impact shown net of effect of hedged items (see Fair Value Hedges section of this Note 4 for further detail)
Fair Value and Notional Amount of Derivatives with Counterparty Credit Risk	The counterparties to these derivatives are financial institutions with the following credit ratings as of December 31: 2017 2016 (In millions) Notional Amount Asset Derivatives Liability Derivatives Notional Amount Asset Derivatives Liability Derivatives Counterparties' credit rating: AA $ 4,708 $ 52 $ (37 ) $ 6,844 $ 247 $ (308 ) A 20,604 271 (370 ) 36,019 900 (1,621 ) BBB 439 8 (67 ) 1,064 60 (69 ) Total $ 25,751 $ 331 $ (474 ) $ 43,927 $ 1,207 $ (1,998 )
Offsetting Assets	Offsetting of Financial Assets and Derivative Assets 2017 Gross Amounts Not Offset (In millions) Gross Amount of Recognized Assets Gross Amount Offset in Balance Sheet Net Amount of Assets Presented in Balance Sheet Financial Instruments Securities Collateral Cash Collateral Received Net Amount Derivative assets: Derivative assets subject to a master netting agreement or offsetting arrangement $ 180 $ 0 $ 180 $ (82 ) $ 0 $ (98 ) $ 0 Derivative assets not subject to a master netting agreement or offsetting arrangement 151 151 151 Total derivative assets 331 0 331 (82 ) 0 (98 ) 151 Securities lending and similar arrangements 592 0 592 0 0 (592 ) 0 Total $ 923 $ 0 $ 923 $ (82 ) $ 0 $ (690 ) $ 151 2016 Gross Amounts Not Offset (In millions) Gross Amount of Recognized Assets Gross Amount Offset in Balance Sheet Net Amount of Assets Presented in Balance Sheet Financial Instruments Securities Collateral Cash Collateral Received Net Amount Derivative assets: Derivative assets subject to a master netting agreement or offsetting arrangement $ 1,080 $ 0 $ 1,080 $ (698 ) $ 0 $ (382 ) $ 0 Derivative assets not subject to a master netting agreement or offsetting arrangement 127 127 127 Total derivative assets 1,207 0 1,207 (698 ) 0 (382 ) 127 Securities lending and similar arrangements 513 0 513 0 0 (513 ) 0 Total $ 1,720 $ 0 $ 1,720 $ (698 ) $ 0 $ (895 ) $ 127
Offsetting Liabilities	Offsetting of Financial Liabilities and Derivative Liabilities 2017 Gross Amounts Not Offset in Balance Sheet (In millions) Gross Amount of Recognized Liabilities Gross Amount Offset in Balance Sheet Net Amount of Liabilities Presented in Balance Sheet Financial Instruments Securities Collateral Cash Collateral Pledged Net Amount Derivative liabilities: Derivative liabilities subject to a master netting agreement or offsetting arrangement $ (346 ) $ 0 $ (346 ) $ 82 $ 245 $ 10 $ (9 ) Derivative liabilities not subject to a master netting agreement or offsetting arrangement (128 ) (128 ) (128 ) Total derivative liabilities (474 ) 0 (474 ) 82 245 10 (137 ) Securities lending and similar arrangements (606 ) 0 (606 ) 592 0 0 (14 ) Total $ (1,080 ) $ 0 $ (1,080 ) $ 674 $ 245 $ 10 $ (151 ) 2016 Gross Amounts Not Offset (In millions) Gross Amount of Recognized Liabilities Gross Amount Offset in Balance Sheet Net Amount of Liabilities Presented in Balance Sheet Financial Instruments Securities Collateral Cash Collateral Pledged Net Amount Derivative liabilities: Derivative liabilities subject to a master netting agreement or offsetting arrangement $ (1,852 ) $ 0 $ (1,852 ) $ 698 $ 1,130 $ 21 $ (3 ) Derivative liabilities not subject to a master netting agreement or offsetting arrangement (146 ) (146 ) (146 ) Total derivative liabilities (1,998 ) 0 (1,998 ) 698 1,130 21 (149 ) Securities lending and similar arrangements (526 ) 0 (526 ) 513 0 0 (13 ) Total $ (2,524 ) $ 0 $ (2,524 ) $ 1,211 $ 1,130 $ 21 $ (162 )

FAIR VALUE MEASUREMENTS (Tables

FAIR VALUE MEASUREMENTS (Tables)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value Hierarchy, Assets and Liabilities Measured on Recurring Basis	The following tables present the fair value hierarchy levels of the Company's assets and liabilities that are measured and carried at fair value on a recurring basis as of December 31. 2017 (In millions) Quoted Prices in Significant Significant Total Assets: Securities available for sale, carried at Fixed maturities: Government and agencies $ 30,109 $ 1,121 $ 0 $ 31,230 Municipalities 0 1,370 0 1,370 Mortgage- and asset-backed securities 0 269 175 444 Public utilities 0 7,886 68 7,954 Sovereign and supranational 0 1,909 0 1,909 Banks/financial institutions 0 7,352 25 7,377 Other corporate 0 32,094 146 32,240 Total fixed maturities 30,109 52,001 414 82,524 Perpetual securities: Banks/financial institutions 0 1,556 0 1,556 Other corporate 0 233 0 233 Total perpetual securities 0 1,789 0 1,789 Equity securities 1,001 6 16 1,023 Other assets: Foreign currency swaps 0 146 150 296 Foreign currency forwards 0 22 0 22 Foreign currency options 0 12 0 12 Credit default swaps 0 0 1 1 Total other assets 0 180 151 331 Other investments 57 0 0 57 Cash and cash equivalents 3,491 0 0 3,491 Total assets $ 34,658 $ 53,976 $ 581 $ 89,215 Liabilities: Other liabilities: Foreign currency swaps $ 0 $ 69 $ 128 $ 197 Foreign currency forwards 0 274 0 274 Foreign currency options 0 3 0 3 Total liabilities $ 0 $ 346 $ 128 $ 474 2016 (In millions) Quoted Prices in Significant Significant Total Assets: Securities available for sale, carried at Fixed maturities: Government and agencies $ 25,387 $ 827 $ 0 $ 26,214 Municipalities 0 1,295 0 1,295 Mortgage- and asset-backed securities 0 1,139 198 1,337 Public utilities 0 7,667 16 7,683 Sovereign and supranational 0 1,469 0 1,469 Banks/financial institutions 0 6,038 25 6,063 Other corporate 0 29,699 0 29,699 Total fixed maturities 25,387 48,134 239 73,760 Perpetual securities: Banks/financial institutions 0 1,420 0 1,420 Other corporate 0 213 0 213 Total perpetual securities 0 1,633 0 1,633 Equity securities 1,300 6 3 1,309 Other assets: Foreign currency swaps 0 365 125 490 Foreign currency forwards 0 672 0 672 Foreign currency options 0 43 0 43 Credit default swaps 0 0 2 2 Total other assets 0 1,080 127 1,207 Other investments 276 0 0 276 Cash and cash equivalents 4,859 0 0 4,859 Total assets $ 31,822 $ 50,853 $ 369 $ 83,044 Liabilities: Other liabilities: Foreign currency swaps $ 0 $ 84 $ 146 $ 230 Foreign currency forwards 0 1,717 0 1,717 Foreign currency options 0 51 0 51 Total liabilities $ 0 $ 1,852 $ 146 $ 1,998
Fair Value Hierarchy Levels of Assets and Liabilities Carried at Cost or Amortized Cost	The following tables present the carrying amount and fair value categorized by fair value hierarchy level for the Company's financial instruments that are not carried at fair value as of December 31. 2017 (In millions) Carrying Quoted Prices in Significant Significant Total Assets: Securities held to maturity, Fixed maturities: Government and agencies $ 21,331 $ 26,491 $ 0 $ 0 $ 26,491 Municipalities 357 0 462 0 462 Mortgage and asset-backed 26 0 8 19 27 Public utilities 3,300 0 3,698 0 3,698 Sovereign and 1,523 0 1,835 0 1,835 Banks/financial institutions 2,206 0 2,387 0 2,387 Other corporate 2,687 0 3,172 0 3,172 Other investments (1) 3,017 0 15 2,987 3,002 Total assets $ 34,447 $ 26,491 $ 11,577 $ 3,006 $ 41,074 Liabilities: Other policyholders’ funds $ 6,939 $ 0 $ 0 $ 6,841 $ 6,841 Notes payable 5,267 0 5,288 265 5,553 Total liabilities $ 12,206 $ 0 $ 5,288 $ 7,106 $ 12,394 (1) Excludes policy loans of $210 and equity method investments of $118 , at carrying value 2016 (In millions) Carrying Quoted Prices in Significant Significant Total Assets: Securities held to maturity, Fixed maturities: Government and agencies $ 20,702 $ 26,040 $ 0 $ 0 $ 26,040 Municipalities 350 0 457 0 457 Mortgage and asset-backed 30 0 10 22 32 Public utilities 3,201 0 3,536 0 3,536 Sovereign and 2,602 0 2,877 0 2,877 Banks/financial institutions 3,731 0 3,900 0 3,900 Other corporate 2,734 0 3,179 0 3,179 Other investments 1,174 0 0 1,142 1,142 Total assets $ 34,524 $ 26,040 $ 13,959 $ 1,164 $ 41,163 Liabilities: Other policyholders’ funds $ 6,659 $ 0 $ 0 $ 6,540 $ 6,540 Notes payable 5,339 0 0 5,530 5,530 Total liabilities $ 11,998 $ 0 $ 0 $ 12,070 $ 12,070
Fair Value Assets Available-for-Sale Securities Primary Pricing Sources	The following tables present the pricing sources for the fair values of the Company's fixed maturities, perpetual securities, and equity securities as of December 31. 2017 (In millions) Quoted Prices in Active Markets for Identical Assets Significant Observable Inputs Significant Unobservable Inputs Total Securities available for sale, carried at fair value: Fixed maturities: Government and agencies: Third party pricing vendor $ 30,109 $ 1,121 $ 0 $ 31,230 Total government and agencies 30,109 1,121 0 31,230 Municipalities: Third party pricing vendor 0 1,370 0 1,370 Total municipalities 0 1,370 0 1,370 Mortgage- and asset-backed securities: Third party pricing vendor 0 269 0 269 Broker/other 0 0 175 175 Total mortgage- and asset-backed securities 0 269 175 444 Public utilities: Third party pricing vendor 0 7,886 0 7,886 Broker/other 0 0 68 68 Total public utilities 0 7,886 68 7,954 Sovereign and supranational: Third party pricing vendor 0 1,807 0 1,807 Broker/other 0 102 0 102 Total sovereign and supranational 0 1,909 0 1,909 Banks/financial institutions: Third party pricing vendor 0 7,352 0 7,352 Broker/other 0 0 25 25 Total banks/financial institutions 0 7,352 25 7,377 Other corporate: Third party pricing vendor 0 32,094 0 32,094 Broker/other 0 0 146 146 Total other corporate 0 32,094 146 32,240 Total fixed maturities 30,109 52,001 414 82,524 Perpetual securities: Banks/financial institutions: Third party pricing vendor 0 1,556 0 1,556 Total banks/financial institutions 0 1,556 0 1,556 Other corporate: Third party pricing vendor 0 233 0 233 Total other corporate 0 233 0 233 Total perpetual securities 0 1,789 0 1,789 Equity securities: Third party pricing vendor 1,001 6 0 1,007 Broker/other 0 0 16 16 Total equity securities 1,001 6 16 1,023 Total securities available for sale $ 31,110 $ 53,796 $ 430 $ 85,336 2016 (In millions) Quoted Prices in Active Markets Significant Observable Significant Unobservable Inputs Total Securities available for sale, carried at fair value: Fixed maturities: Government and agencies: Third party pricing vendor $ 25,387 $ 827 $ 0 $ 26,214 Total government and agencies 25,387 827 0 26,214 Municipalities: Third party pricing vendor 0 1,295 0 1,295 Total municipalities 0 1,295 0 1,295 Mortgage- and asset-backed securities: Third party pricing vendor 0 1,139 0 1,139 Broker/other 0 0 198 198 Total mortgage- and asset-backed securities 0 1,139 198 1,337 Public utilities: Third party pricing vendor 0 7,667 0 7,667 Broker/other 0 0 16 16 Total public utilities 0 7,667 16 7,683 Sovereign and supranational: Third party pricing vendor 0 1,469 0 1,469 Total sovereign and supranational 0 1,469 0 1,469 Banks/financial institutions: Third party pricing vendor 0 6,038 0 6,038 Broker/other 0 0 25 25 Total banks/financial institutions 0 6,038 25 6,063 Other corporate: Third party pricing vendor 0 29,699 0 29,699 Total other corporate 0 29,699 0 29,699 Total fixed maturities 25,387 48,134 239 73,760 Perpetual securities: Banks/financial institutions: Third party pricing vendor 0 1,420 0 1,420 Total banks/financial institutions 0 1,420 0 1,420 Other corporate: Third party pricing vendor 0 213 0 213 Total other corporate 0 213 0 213 Total perpetual securities 0 1,633 0 1,633 Equity securities: Third party pricing vendor 1,300 6 0 1,306 Broker/other 0 0 3 3 Total equity securities 1,300 6 3 1,309 Total securities available for sale $ 26,687 $ 49,773 $ 242 $ 76,702
Fair Value Assets Held-To-Maturity Securities Primary Pricing Sources	2016 (In millions) Quoted Prices in Active Markets Significant Observable Significant Unobservable Inputs Total Securities held to maturity, carried at amortized cost: Fixed maturities: Government and agencies: Third party pricing vendor $ 26,040 $ 0 $ 0 $ 26,040 Total government and agencies 26,040 0 0 26,040 Municipalities: Third party pricing vendor 0 457 0 457 Total municipalities 0 457 0 457 Mortgage- and asset-backed securities: Third party pricing vendor 0 10 0 10 Broker/other 0 0 22 22 Total mortgage- and asset-backed securities 0 10 22 32 Public utilities: Third party pricing vendor 0 3,536 0 3,536 Total public utilities 0 3,536 0 3,536 Sovereign and supranational: Third party pricing vendor 0 2,877 0 2,877 Total sovereign and supranational 0 2,877 0 2,877 Banks/financial institutions: Third party pricing vendor 0 3,900 0 3,900 Total banks/financial institutions 0 3,900 0 3,900 Other corporate: Third party pricing vendor 0 3,179 0 3,179 Total other corporate 0 3,179 0 3,179 Total securities held to maturity $ 26,040 $ 13,959 $ 22 $ 40,021 2017 (In millions) Quoted Prices in Active Markets for Identical Assets Significant Observable Inputs Significant Unobservable Inputs Total Securities held to maturity, carried at amortized cost: Fixed maturities: Government and agencies: Third party pricing vendor $ 26,491 $ 0 $ 0 $ 26,491 Total government and agencies 26,491 0 0 26,491 Municipalities: Third party pricing vendor 0 462 0 462 Total municipalities 0 462 0 462 Mortgage- and asset-backed securities: Third party pricing vendor 0 8 0 8 Broker/other 0 0 19 19 Total mortgage- and asset-backed securities 0 8 19 27 Public utilities: Third party pricing vendor 0 3,698 0 3,698 Total public utilities 0 3,698 0 3,698 Sovereign and supranational: Third party pricing vendor 0 1,835 0 1,835 Total sovereign and supranational 0 1,835 0 1,835 Banks/financial institutions: Third party pricing vendor 0 2,387 0 2,387 Total banks/financial institutions 0 2,387 0 2,387 Other corporate: Third party pricing vendor 0 3,172 0 3,172 Total other corporate 0 3,172 0 3,172 Total securities held to maturity $ 26,491 $ 11,562 $ 19 $ 38,072
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation	The following tables present the changes in fair value of the Company's available-for-sale investments and derivatives classified as Level 3 as of December 31. 2017 Fixed Maturities Equity Derivatives (1) (In millions) Mortgage- Public Banks/ Other Foreign Credit Total Balance, beginning of period $ 198 $ 16 $ 25 $ 0 $ 3 $ (21 ) $ 2 $ 223 Realized investment gains (losses) included 0 0 0 0 0 43 (1 ) 42 Unrealized gains (losses) included in other 3 0 0 2 0 0 0 5 Purchases, issuances, sales and settlements: Purchases 0 76 0 122 16 0 0 214 Issuances 0 0 0 0 0 0 0 0 Sales 0 0 0 (2 ) (1 ) 0 0 (3 ) Settlements (26 ) 0 0 0 0 0 0 (26 ) Transfers into Level 3 0 0 0 24 (2) 0 0 0 24 Transfers out of Level 3 0 (24 ) (2) 0 0 (2 ) (3) 0 0 (26 ) Balance, end of period $ 175 $ 68 $ 25 $ 146 $ 16 $ 22 $ 1 $ 453 Changes in unrealized gains (losses) relating $ 0 $ 0 $ 0 $ 0 $ 0 $ 43 $ (1 ) $ 42 (1) Derivative assets and liabilities are presented net (2) Transfer due to sector classification change (3) Transfer due to change in accounting method 2016 Fixed Maturities Equity Derivatives (1) (In millions) Mortgage- Public Banks/ Other Foreign Credit Total Balance, beginning of period $ 220 $ 0 $ 26 $ 0 $ 3 $ (192 ) $ 1 $ 58 Realized investment gains (losses) included in 0 0 0 0 0 194 1 195 Unrealized gains (losses) included in other 38 0 (1 ) 0 0 (22 ) 0 15 Purchases, issuances, sales and settlements: Purchases 0 16 0 0 0 0 0 16 Issuances 0 0 0 0 0 0 0 0 Sales 0 0 0 0 0 0 0 0 Settlements (60 ) 0 0 0 0 (1 ) 0 (61 ) Transfers into Level 3 0 0 0 0 0 0 0 0 Transfers out of Level 3 0 0 0 0 0 0 0 0 Balance, end of period $ 198 $ 16 $ 25 $ 0 $ 3 $ (21 ) $ 2 $ 223 Changes in unrealized gains (losses) relating $ 0 $ 0 $ 0 $ 0 $ 0 $ 194 $ 1 $ 195 (1) Derivative assets and liabilities are presented net
Fair Value Inputs Assets Quantitative Information	2016 (In millions) Fair Value Valuation Technique(s) Unobservable Input Range Assets: Securities available for sale, carried at fair value: Fixed maturities: Mortgage- and asset-backed securities $ 198 Consensus pricing Offered quotes N/A (d) Public utilities 16 Discounted cash flow Historical volatility N/A (d) Banks/financial institutions 25 Consensus pricing Offered quotes N/A (d) Equity securities 3 Net asset value Offered quotes $1-$701 ($8) Other assets: Foreign currency swaps 16 Discounted cash flow Interest rates (USD) 2.34% - 2.59% (a) Interest rates (JPY) .22% - .80% (b) CDS spreads 17 - 172 bps Foreign exchange rates 21.47% (c) 29 Discounted cash flow Interest rates (USD) 2.34% - 2.59% (a) Interest rates (JPY) .22% - .80% (b) CDS spreads 16 - 88 bps 80 Discounted cash flow Interest rates (USD) 2.34% - 2.59% (a) Interest rates (JPY) .22% - .80% (b) Foreign exchange rates 21.47% (c) Credit default swaps 2 Discounted cash flow Base correlation 52.18% - 56.07% (e) CDS spreads 54 bps Recovery rate 36.69% Total assets $ 369 (a) Inputs derived from U.S. long-term rates to accommodate long maturity nature of the Company's swaps (b) Inputs derived from Japan long-term rates to accommodate long maturity nature of the Company's swaps (c) Based on 10 year volatility of JPY/USD exchange rate (d) N/A represents securities where the Company receives unadjusted broker quotes and for which there is no transparency into the providers' valuation techniques or unobservable inputs. (e) Range of base correlation for the Company's bespoke tranche for attachment and detachment points corresponding to market indices The following tables summarize the significant unobservable inputs used in the valuation of the Company's Level 3 available-for-sale investments and derivatives as of December 31. Included in the tables are the inputs or range of possible inputs that have an effect on the overall valuation of the financial instruments. 2017 (In millions) Fair Value Valuation Technique(s) Unobservable Input Range Assets: Securities available for sale, carried at fair value: Fixed maturities: Mortgage- and asset-backed securities $ 175 Consensus pricing Offered quotes N/A (c) Public utilities 68 Discounted cash flow Credit spreads N/A (c) Banks/financial institutions 25 Consensus pricing Offered quotes N/A (c) Other corporate 146 Discounted cash flow Credit spreads N/A (d) Equity securities 16 Net asset value Offered quotes N/A (c) Other assets: Foreign currency swaps 80 Discounted cash flow Interest rates (USD) 2.40% - 2.54% (a) Interest rates (JPY) .26% - .85% (b) CDS spreads 9 - 90 bps 70 Discounted cash flow Interest rates (USD) 2.40% - 2.54% (a) Interest rates (JPY) .26% - .85% (b) Credit default swaps 1 Discounted cash flow Base correlation 46.33% - 49.65% (d) CDS spreads 25 bps Recovery rate 37.24% Total assets $ 581 (a) Inputs derived from U.S. long-term rates to accommodate long maturity nature of the Company's swaps (b) Inputs derived from Japan long-term rates to accommodate long maturity nature of the Company's swaps (c) N/A represents securities where the Company receives unadjusted broker quotes and for which there is no transparency into the providers' valuation techniques or unobservable inputs. (d) Range of base correlation for the Company's bespoke tranche for attachment and detachment points corresponding to market indices
Fair Value Inputs Liabilities Quantitative Information	2017 (In millions) Fair Value Valuation Technique(s) Unobservable Input Range Liabilities: Other liabilities: Foreign currency swaps 120 Discounted cash flow Interest rates (USD) 2.40% - 2.54% (a) Interest rates (JPY) .26% - .85% (b) CDS spreads 13 - 157 bps 8 Discounted cash flow Interest rates (USD) 2.40% - 2.54% (a) Interest rates (JPY) .26% - .85% (b) Total liabilities $ 128 (a) Inputs derived from U.S. long-term rates to accommodate long maturity nature of the Company's swaps (b) Inputs derived from Japan long-term rates to accommodate long maturity nature of the Company's swaps 2016 (In millions) Fair Value Valuation Technique(s) Unobservable Input Range Liabilities: Other liabilities: Foreign currency swaps $ 113 Discounted cash flow Interest rates (USD) 2.34% - 2.59% (a) Interest rates (JPY) .22% - .80% (b) CDS spreads 17 - 172 bps Foreign exchange rates 21.47% (c) 23 Discounted cash flow Interest rates (USD) 2.34% - 2.59% (a) Interest rates (JPY) .22% - .80% (b) CDS spreads 24 - 216 bps 10 Discounted cash flow Interest rates (USD) 2.34% - 2.59% (a) Interest rates (JPY) .22% - .80% (b) Foreign exchange rates 21.47% (c) Total liabilities $ 146 (a) Inputs derived from U.S. long-term rates to accommodate long maturity nature of the Company's swaps (b) Inputs derived from Japan long-term rates to accommodate long maturity nature of the Company's swaps (c) Based on 10 year volatility of JPY/USD exchange rate

DEFERRED POLICY ACQUISITION C34

DEFERRED POLICY ACQUISITION COSTS AND INSURANCE EXPENSES (Tables)	12 Months Ended
	Dec. 31, 2017
Deferred Policy Acquisition Costs Disclosures [Abstract]
Schedule of Deferred Policy Acquisition Costs	The following table presents a rollforward of deferred policy acquisition costs by segment for the years ended December 31. 2017 2016 (In millions) Japan U.S. Japan U.S. Deferred policy acquisition costs: Balance, beginning of year $ 5,765 $ 3,228 $ 5,370 $ 3,141 Capitalization 839 629 864 583 Amortization (630 ) (502 ) (644 ) (497 ) Foreign currency translation and other 176 0 175 1 Balance, end of year $ 6,150 $ 3,355 $ 5,765 $ 3,228
Advertising Expense	Advertising expense, which is included in insurance expenses in the consolidated statements of earnings, was as follows for the years ended December 31: (In millions) 2017 2016 2015 Advertising expense: Aflac Japan $ 100 $ 100 $ 82 Aflac U.S. 110 124 129 Total advertising expense $ 210 $ 224 $ 211
Schedule Of Depreciation And Amortization Expense	Depreciation and other amortization expenses, which are included in insurance expenses in the consolidated statements of earnings, were as follows for the years ended December 31: (In millions) 2017 2016 2015 Depreciation expense $ 50 $ 48 $ 44 Other amortization expense 3 6 6 Total depreciation and other amortization expense $ 53 $ 54 $ 50
Schedule of Lease Expenses	Lease and rental expense, which are included in insurance expenses in the consolidated statements of earnings, were as follows for the years ended December 31: (In millions) 2017 2016 2015 Lease and rental expense: Aflac Japan $ 52 $ 53 $ 46 Aflac U.S. 21 21 18 Other 2 1 1 Total lease and rental expense $ 75 $ 75 $ 65

POLICY LIABILITIES (Tables)

POLICY LIABILITIES (Tables)	12 Months Ended
	Dec. 31, 2017
Insurance Loss Reserves [Abstract]
Liability for Future Policy Benefits by Product Segment	The liability for future policy benefits as of December 31 consisted of the following: Liability Amounts Interest Rates (In millions) Policy 2017 2016 Year of In 20 Health insurance: Japan: 1992 - 2017 $ 10,167 $ 8,912 1.0 - 2.5 % 1.0 - 2.5 % 1974 - 2013 1,133 1,118 2.7 - 2.75 2.25 - 2.75 1998 - 2017 12,386 11,687 3.0 3.0 1997 - 1999 2,454 2,485 3.5 3.5 1994 - 1996 3,046 3,069 4.0 - 4.5 4.0 - 4.5 1987 - 1994 14,829 14,372 5.5 5.5 1985 - 1991 1,816 1,871 5.25 - 6.75 5.25 - 5.5 1978 - 1984 2,037 2,134 6.5 5.5 U.S.: 2013 - 2017 82 75 3.0 3.0 2012 - 2017 1,366 1,062 3.75 3.75 2011 343 319 4.75 4.75 2005 - 2010 2,944 3,004 5.5 5.5 1988 - 2004 656 669 8.0 6.0 1986 - 2004 1,296 1,265 6.0 6.0 1981 - 1986 159 166 6.5 - 7.0 5.5 - 6.5 1998 - 2004 1,310 1,295 7.0 7.0 Other 18 19 Intercompany eliminations: 2015 (609 ) (1) (630 ) (1) 2.0 2.0 Life insurance: Japan: 2001 - 2017 8,850 7,255 1.0 - 1.85 1.0 - 1.85 2011 - 2017 4,763 4,151 2.0 2.0 2009 - 2011 3,393 2,861 2.25 2.25 1992 - 2006 5 5 2.19 1.55 2005 - 2011 1,642 1,488 2.5 2.5 1985 - 2006 2,048 2,007 2.7 2.25 2007 - 2011 1,319 1,220 2.75 2.75 1999 - 2011 2,189 2,102 3.0 3.0 1996 - 2009 675 657 3.5 3.5 1994 - 1996 908 897 4.0 - 4.5 4.0 - 4.5 U.S.: 1956 - 2017 632 571 3.5 - 6.0 3.5 - 6.0 Total $ 81,857 $ 76,106 (1) Elimination entry necessary due to recapture of a portion of policy liabilities ceded externally, as a result of the reinsurance retrocession transaction as described in Note 8 of the Notes to the Consolidated Financial Statements
Schedule of Liability for Unpaid Claims Adjustment Expense	Changes in the liability for unpaid policy claims were as follows for the years ended December 31: (In millions) 2017 2016 2015 Unpaid supplemental health claims, beginning of period $ 3,707 $ 3,548 $ 3,412 Less reinsurance recoverables 27 26 7 Net balance, beginning of period 3,680 3,522 3,405 Add claims incurred during the period related to: Current year 6,979 7,037 6,416 Prior years (518 ) (465 ) (353 ) Total incurred 6,461 6,572 6,063 Less claims paid during the period on claims incurred during: Current year 4,530 4,613 4,227 Prior years 1,822 1,865 1,718 Total paid 6,352 6,478 5,945 Effect of foreign exchange rate changes on unpaid claims 65 64 (1 ) Net balance, end of period 3,854 3,680 3,522 Add reinsurance recoverables 30 27 26 Unpaid supplemental health claims, end of period 3,884 3,707 3,548 Unpaid life claims, end of period 508 338 254 Total liability for unpaid policy claims $ 4,392 $ 4,045 $ 3,802

REINSURANCE (Tables)

REINSURANCE (Tables)	12 Months Ended
	Dec. 31, 2017
Reinsurance Disclosures [Abstract]
Effects of Reinsurance	The following table reconciles direct premium income and direct benefits and claims to net amounts after the effect of reinsurance for the years ended December 31. (In millions) 2017 2016 Direct premium income $ 18,875 $ 19,592 Ceded to other companies: Ceded Aflac Japan closed blocks (515 ) (560 ) Other (51 ) (48 ) Assumed from other companies: Retrocession activities 216 234 Other 6 7 Net premium income $ 18,531 $ 19,225 Direct benefits and claims $ 12,486 $ 13,240 Ceded benefits and change in reserves for future benefits: Ceded Aflac Japan closed blocks (473 ) (509 ) Eliminations 51 58 Other (44 ) (38 ) Assumed from other companies: Retrocession activities 209 222 Eliminations (51 ) (58 ) Other 3 4 Benefits and claims, net $ 12,181 $ 12,919

NOTES PAYABLE (Tables)

NOTES PAYABLE (Tables)	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Schedule of Long-term Debt Instruments	A summary of notes payable as of December 31 follows: (In millions) 2017 2016 2.65% senior notes paid February 2017 $ 0 $ 649 2.40% senior notes due March 2020 548 547 4.00% senior notes due February 2022 348 348 3.625% senior notes due June 2023 697 696 3.625% senior notes due November 2024 745 745 3.25% senior notes due March 2025 446 445 2.875% senior notes due October 2026 297 298 6.90% senior notes due December 2039 220 220 6.45% senior notes due August 2040 254 254 4.00% senior notes due October 2046 394 394 5.50% subordinated debentures due September 2052 0 (1) 486 Yen-denominated senior notes and subordinated debentures: .932% senior notes due January 2027 (principal amount 60.0 billion yen) 528 0 2.108% subordinated debentures due October 2047 (principal amount 60.0 billion yen) 526 0 Yen-denominated loans: Variable interest rate loan due September 2021 (.32% in 2017 and .31% in 2016, principal amount 5.0 billion yen) 44 43 Variable interest rate loan due September 2023 (.47% in 2017 and .46% in 2016, principal amount 25.0 billion yen) 220 214 Capitalized lease obligations payable through 2024 22 21 Total notes payable $ 5,289 $ 5,360 (1) Redeemed in November 2017 Amounts in the table above are reported net of debt issuance costs and issuance premiums or discounts, if applicable, that are being amortized over the life of the notes.
Schedule of Maturities of Long Term Debt	The aggregate contractual maturities of notes payable during each of the years after December 31, 2017 , are as follows: (In millions) Long-term Capitalized Total 2018 $ 0 $ 8 $ 8 2019 0 7 7 2020 550 3 553 2021 44 2 46 2022 350 1 351 Thereafter 4,364 1 4,365 Total $ 5,308 $ 22 $ 5,330
Schedule of Line of Credit Facilities	A summary of the Company's lines of credit as of December 31, 2017 follows: Borrower Type Original Term Expiration Date Capacity Amount Outstanding Interest Rate on Borrowed Amount Maturity Period Commitment Fee Business Purpose Aflac Incorporated uncommitted bilateral 364 days November 30, 2018 $100 million $0 million The rate quoted by the bank and agreed upon at the time of borrowing Up to 3 months None General corporate purposes Aflac Incorporated unsecured revolving 3 years March 31, 2019, or the date commitments are terminated pursuant to an event of default 100.0 billion yen 0.0 billion yen A rate per annum equal to (a) Tokyo interbank market rate (TIBOR) plus, the alternative applicable TIBOR margin during the availability period from the closing date to the commitment termination date or (b) the TIBOR rate offered by the agent to major banks in yen for the applicable period plus, the applicable alternative TIBOR margin during the term out period No later than .30% to .50%, depending on the Parent Company's debt ratings as of the date of determination General corporate purposes, including a capital contingency plan for the operations of the Parent Company Aflac Incorporated unsecured revolving 5 years September 18, 2020, or the date commitments are terminated pursuant to an event of default 55.0 billion yen, or the equivalent amount in U.S. dollars 0.0 billion yen A rate per annum equal to, at the Company's option, either, (a) London Interbank Offered Rate (LIBOR) adjusted for certain costs or (b) a base rate determined by reference to the highest of (1) the federal funds rate plus 1/2 of 1%, (2) the rate of interest for such day announced by Mizuho Bank, Ltd. as its prime rate, or (3) the eurocurrency rate for an interest period of one month plus 1.00%, in each case plus an applicable margin No later than September 18, 2020 .085% to .225%, depending on the Parent Company's debt ratings as of the date of determination General corporate purposes, including a capital contingency plan for the operations of the Parent Company Aflac Incorporated uncommitted bilateral None specified None specified $50 million $0 million A rate per annum equal to, at the Parent Company's option, either (a) a eurocurrency rate determined by reference to the agent's LIBOR for the interest period relevant to such borrowing or (b) the base rate determined by reference to the greater of (i) the prime rate as determined by the agent, and (ii) the sum of 0.50% and the federal funds rate for such day Up to 3 months None General corporate purposes Aflac (1) uncommitted revolving 364 days November 30, 2018 $250 million $65 million USD three-month LIBOR plus 75 basis points per annum 3 months None General corporate purposes Aflac Incorporated (1) uncommitted revolving 364 days April 2, 2018 37.5 billion yen 0.0 billion yen Three-month TIBOR plus 80 basis points per annum 3 months None General corporate purposes (1) Intercompany credit agreement

INCOME TAXES (Tables)

INCOME TAXES (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Schedule of Components of Income Tax Expense (Benefit)	The components of income tax expense (benefit) applicable to pretax earnings for the years ended December 31 were as follows: (In millions) Foreign U.S. Total 2017: Current $ 722 $ (91 ) $ 631 Deferred (24 ) (1,193 ) (1,217 ) Total income tax expense $ 698 $ (1,284 ) $ (586 ) 2016: Current $ 650 $ 234 $ 884 Deferred 136 388 524 Total income tax expense $ 786 $ 622 $ 1,408 2015: Current $ 1,063 $ 225 $ 1,288 Deferred 42 (1 ) 41 Total income tax expense $ 1,105 $ 224 $ 1,329
Schedule of Effective Income Tax Rate Reconciliation	The principal reasons for the differences and the related tax effects for the years ended December 31 were as follows: (In millions) 2017 2016 2015 Income taxes based on U.S. statutory rates $ 1,406 $ 1,424 $ 1,352 Write-down of U.S. deferred tax liabilities for tax reform change (1,933 ) 0 0 Utilization of foreign tax credit (27 ) (30 ) (27 ) Nondeductible expenses 10 8 3 Other, net (42 ) 6 1 Income tax expense $ (586 ) $ 1,408 $ 1,329
Schedule of Income Tax Expense Benefit Intraperiod Tax Allocation	Total income tax expense for the years ended December 31 was allocated as follows: (In millions) 2017 2016 2015 Statements of earnings $ (586 ) $ 1,408 $ 1,329 Other comprehensive income (loss): Unrealized foreign currency translation gains (losses) during period 52 70 16 Unrealized gains (losses) on investment securities: Unrealized holding gains (losses) on investment 575 962 (931 ) Reclassification adjustment for realized (gains) losses 1 18 21 Unrealized gains (losses) on derivatives during period 0 1 0 Pension liability adjustment during period 3 (16 ) (7 ) Total income tax expense (benefit) related to items of 631 1,035 (901 ) Additional paid-in capital (exercise of stock options) 0 (10 ) 4 Total income taxes $ 45 $ 2,433 $ 432
Schedule of Deferred Tax Assets and Liabilities	The income tax effects of the temporary differences that gave rise to deferred income tax assets and liabilities as of December 31 were as follows: (In millions) 2017 2016 Deferred income tax liabilities: Deferred policy acquisition costs $ 3,285 $ 4,065 Unrealized gains and other basis differences on investment securities 2,882 3,056 Premiums receivable 104 130 Policy benefit reserves 3,557 3,303 Total deferred income tax liabilities 9,828 10,554 Deferred income tax assets: Unfunded retirement benefits 8 13 Other accrued expenses 141 39 Policy and contract claims 870 792 Foreign currency loss on Japan branch 67 185 Deferred compensation 155 243 Capital loss carryforwards 0 3 Depreciation 114 88 Anticipatory foreign tax credit 4,504 4,028 Other 57 107 Total deferred income tax assets before valuation allowance 5,916 5,498 Valuation allowance (657 ) 0 Total deferred income tax assets after valuation allowance 5,259 5,498 Net deferred income tax liability 4,569 5,056 Current income tax liability 176 331 Total income tax liability $ 4,745 $ 5,387
Summary of Income Tax Contingencies	A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows for the years ended December 31: (In millions) 2017 2016 Balance, beginning of year $ 294 $ 264 Additions for tax positions of prior years 0 33 Reductions for tax positions of prior years (280 ) (3 ) Balance, end of year $ 14 $ 294

SHAREHOLDERS' EQUITY (Tables)

SHAREHOLDERS' EQUITY (Tables)	12 Months Ended
	Dec. 31, 2017
Stockholders' Equity Note [Abstract]
Schedule of Common Stock Outstanding Roll Forward	The following table is a reconciliation of the number of shares of the Company's common stock for the years ended December 31. (In thousands of shares) 2017 2016 2015 Common stock - issued: Balance, beginning of period 671,249 669,723 668,132 Exercise of stock options and issuance of restricted shares 1,632 1,526 1,591 Balance, end of period 672,881 671,249 669,723 Treasury stock: Balance, beginning of period 265,439 245,343 225,687 Purchases of treasury stock: Open market 17,755 21,618 21,179 Other 509 330 247 Dispositions of treasury stock: Shares issued to AFL Stock Plan (891) (1,064) (1,209) Exercise of stock options (367) (683) (465) Other (19) (105) (96) Balance, end of period 282,426 265,439 245,343 Shares outstanding, end of period 390,455 405,810 424,380
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share	The following table presents the approximate number of share-based awards to purchase shares, on a weighted-average basis, that were considered to be anti-dilutive and were excluded from the calculation of diluted earnings per share at December 31: (In thousands) 2017 2016 2015 Anti-dilutive share-based awards 255 911 1,862
Schedule of Weighted Average Number of Shares	The weighted-average shares used in calculating earnings per share for the years ended December 31 were as follows: (In thousands of shares) 2017 2016 2015 Weighted-average outstanding shares used for calculating basic EPS 396,021 411,471 430,654 Dilutive effect of share-based awards 2,909 2,450 2,518 Weighted-average outstanding shares used for calculating diluted EPS 398,930 413,921 433,172
Changes in Accumulated Other Comprehensive Income (Detail)	The tables below are reconciliations of accumulated other comprehensive income by component for the years ended December 31. Changes in Accumulated Other Comprehensive Income 2017 (In millions) Unrealized Foreign Unrealized Unrealized Pension Total Balance, beginning of period $ (1,983 ) $ 4,805 $ (24 ) $ (168 ) $ 2,630 Other comprehensive 233 1,158 1 (6 ) 1,386 Amounts reclassified from 0 1 0 11 12 Net current-period other 233 1,159 1 5 1,398 Balance, end of period $ (1,750 ) $ 5,964 $ (23 ) $ (163 ) $ 4,028 All amounts in the table above are net of tax. 2016 (In millions) Unrealized Foreign Unrealized Unrealized Pension Liability Adjustment Total Balance, beginning of period $ (2,196 ) $ 2,986 $ (26 ) $ (139 ) $ 625 Other comprehensive 213 1,854 2 (32 ) 2,037 Amounts reclassified from 0 (35 ) 0 3 (32 ) Net current-period other 213 1,819 2 (29 ) 2,005 Balance, end of period $ (1,983 ) $ 4,805 $ (24 ) $ (168 ) $ 2,630 All amounts in the table above are net of tax. 2015 (In millions) Unrealized Foreign Unrealized Unrealized Pension Liability Adjustment Total Balance, beginning of period $ (2,541 ) $ 4,672 $ (26 ) $ (126 ) $ 1,979 Other comprehensive 345 (1,646 ) 0 (13 ) (1,314 ) Amounts reclassified from 0 (40 ) 0 0 (40 ) Net current-period other 345 (1,686 ) 0 (13 ) (1,354 ) Balance, end of period $ (2,196 ) $ 2,986 $ (26 ) $ (139 ) $ 625 All amounts in the table above are net of tax.
Reclassification out of Accumulated Other Comprehensive Income [Table Text Block]	The tables below summarize the amounts reclassified from each component of accumulated other comprehensive income based on source for the years ended December 31. Reclassifications Out of Accumulated Other Comprehensive Income (In millions) 2017 Details about Accumulated Other Comprehensive Income Components Amount Reclassified from Accumulated Other Comprehensive Income Affected Line Item in the Unrealized gains (losses) on available-for-sale $ 27 Sales and redemptions (29 ) Other-than-temporary impairment (2 ) Total before tax 1 Tax (expense) or benefit (1) $ (1 ) Net of tax Amortization of defined benefit pension items: Actuarial gains (losses) $ (17 ) Acquisition and operating expenses (2) Prior service (cost) credit 0 Acquisition and operating expenses (2) 6 Tax (expense) or benefit (1) $ (11 ) Net of tax Total reclassifications for the period $ (12 ) Net of tax (1) Based on 35% tax rate (2) These accumulated other comprehensive income components are included in the computation of net periodic pension cost (see Note 14 for additional details). (In millions) 2016 Details about Accumulated Other Comprehensive Income Components Amount Reclassified from Accumulated Other Comprehensive Income Affected Line Item in the Unrealized gains (losses) on available-for-sale $ 136 Sales and redemptions (83 ) Other-than-temporary impairment 53 Total before tax (18 ) Tax (expense) or benefit (1) $ 35 Net of tax Amortization of defined benefit pension items: Actuarial gains (losses) $ (15 ) Acquisition and operating expenses (2) Prior service (cost) credit 11 Acquisition and operating expenses (2) 1 Tax (expense) or benefit (1) $ (3 ) Net of tax Total reclassifications for the period $ 32 Net of tax (1) Based on 35% tax rate (2) These accumulated other comprehensive income components are included in the computation of net periodic pension cost (see Note 14 for additional details). (In millions) 2015 Details about Accumulated Other Comprehensive Income Components Amount Reclassified from Accumulated Other Comprehensive Income Affected Line Item in the Unrealized gains (losses) on available-for-sale $ 214 Sales and redemptions (153 ) Other-than-temporary impairment 61 Total before tax (21 ) Tax (expense) or benefit (1) $ 40 Net of tax Amortization of defined benefit pension items: Actuarial gains (losses) $ (17 ) Acquisition and operating expenses (2) Prior service (cost) credit 17 Acquisition and operating expenses (2) 0 Tax (expense) or benefit (1) $ 0 Net of tax Total reclassifications for the period $ 40 Net of tax (1) Based on 35% tax rate (2) These accumulated other comprehensive income components are included in the computation of net periodic pension cost (see Note 14 for additional details).

SHARE-BASED COMPENSATION (Table

SHARE-BASED COMPENSATION (Tables)	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Schedule of Expense Recognized in Connection with Share Based Awards	The following table presents the impact of the expense recognized in connection with share-based awards for the periods ended December 31. (In millions, except for per-share amounts) 2017 2016 2015 Impact on earnings from continuing operations $ 51 $ 68 $ 39 Impact on earnings before income taxes 51 68 39 Impact on net earnings 35 46 27 Impact on net earnings per share: Basic $ .09 $ .11 $ .06 Diluted .09 .11 .06
Schedule of Share-based Compensation, Stock Options, Activity	The following table summarizes stock option activity under the the employee stock option plan. (In thousands of shares) Stock Weighted-Average Outstanding at December 31, 2014 9,307 $ 48.84 Granted in 2015 855 61.47 Canceled in 2015 (231 ) 55.70 Exercised in 2015 (2,013 ) 45.15 Outstanding at December 31, 2015 7,918 50.94 Granted in 2016 664 61.39 Canceled in 2016 (181 ) 55.63 Exercised in 2016 (2,061 ) 48.91 Outstanding at December 31, 2016 6,340 52.56 Granted in 2017 313 71.60 Canceled in 2017 (118 ) 49.90 Exercised in 2017 (2,883 ) 60.22 Outstanding at December 31, 2017 3,652 $ 56.05
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Exercisable	(In thousands of shares) 2017 2016 2015 Shares exercisable, end of year 2,104 4,493 6,085
Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions	The following table presents the assumptions used in valuing options granted during the years ended December 31. 2017 2016 2015 Expected term (years) 5.9 6.4 6.3 Expected volatility 26.0 % 27.0 % 20.0 % Annual forfeiture rate 3.4 3.2 2.8 Risk-free interest rate 2.5 2.2 2.0 Dividend yield 2.5 2.9 2.7
Schedule of Share-based Compensation, Shares Authorized under Stock Option Plans, by Exercise Price Range	The following table summarizes information about stock options outstanding and exercisable at December 31, 2017 . (In thousands of shares) Options Outstanding Options Exercisable Range of Stock Option Wgtd.-Avg. Wgtd.-Avg. Stock Option Wgtd.-Avg. $ 22.13 - $ 48.56 823 2.5 $ 38.56 823 $ 38.56 49.50 - 57.93 1,034 5.5 55.64 608 54.04 58.08 - 61.81 748 5.5 61.29 234 61.22 61.95 - 71.04 944 7.4 65.69 439 63.06 71.84 - 87.71 103 9.0 73.53 0 0.00 $ 22.13 - $ 87.71 3,652 5.4 $ 56.05 2,104 $ 50.67
Schedule of Cash Proceeds Received from Share-based Payment Awards	The following table summarizes stock option activity during the years ended December 31. (In millions) 2017 2016 2015 Total intrinsic value of options exercised $ 87 $ 41 $ 36 Cash received from options exercised 58 68 68 Tax benefit realized as a result of options exercised and 74 45 25
Schedule of Share-based Payment Award, Performance Based Restricted Stock, Valuation Assumptions	Key assumptions used to value PBRS granted during 2017 follows: (In millions) 2017 Expected volatility (based on Aflac Inc. and peer group historical daily stock price) 16.59 % Expected life from grant date (years) 2.9 Risk-free interest rate (based on U.S. Treasury yields at the date of grant) 1.56 %
Schedule of Nonvested Restricted Stock Units Activity	The value of restricted stock awards and restricted stock units is based on the fair market value of our common stock at the date of grant. The following table summarizes restricted stock activity during the years ended December 31. (In thousands of shares) Shares Weighted-Average Restricted stock at December 31, 2014 1,880 $ 54.33 Granted in 2015 638 61.51 Canceled in 2015 (145 ) 57.52 Vested in 2015 (558 ) 48.41 Restricted stock at December 31, 2015 1,815 58.42 Granted in 2016 878 61.68 Canceled in 2016 (76 ) 60.65 Vested in 2016 (749 ) 53.68 Restricted stock at December 31, 2016 1,868 61.76 Granted in 2017 559 72.95 Canceled in 2017 (101 ) 64.45 Vested in 2017 (509 ) 62.17 Restricted stock at December 31, 2017 1,817 $ 64.80

STATUTORY ACCOUNTING AND DIVI41

STATUTORY ACCOUNTING AND DIVIDEND RESTRICTIONS (Tables)	12 Months Ended
	Dec. 31, 2017
Insurance [Abstract]
Reconciliation of Capital and Surplus between NAIC and Nebraska state basis	A reconciliation of Aflac's capital and surplus between SAP and practices permitted by the state of Nebraska is shown below: (In millions) 2017 2016 Capital and surplus, Nebraska state basis $ 11,001 $ 11,221 State Permitted Practice: Refundable lease deposits – Japan (43 ) (40 ) Reinsurance - Japan (818 ) (764 ) Capital and surplus, NAIC basis $ 10,140 $ 10,417
Profits Repatriated Disclosure	Profits repatriated by Aflac Japan to Aflac U.S. were as follows for the years ended December 31: In Dollars In Yen (In millions of dollars and billions of yen) 2017 2016 2015 2017 2016 2015 Profit repatriation $ 1,150 $ 1,286 $ 2,139 129.3 138.5 259.0

BENEFIT PLANS (Tables)

BENEFIT PLANS (Tables)	12 Months Ended
	Dec. 31, 2017
Schedule of Net Funded Status	Information with respect to the Company's benefit plans' assets and obligations as of December 31 was as follows: Pension Benefits Other Japan U.S. Postretirement Benefits (In millions) 2017 2016 2017 2016 2017 2016 Projected benefit obligation: Benefit obligation, beginning of year $ 329 $ 276 $ 798 $ 735 $ 37 $ 40 Service cost 20 16 24 23 0 1 Interest cost 6 9 40 29 1 2 Actuarial (gain) loss (10 ) 29 65 29 0 (4 ) Benefits and expenses paid (14 ) (8 ) (19 ) (18 ) (2 ) (2 ) Effect of foreign exchange 10 7 0 0 0 0 Benefit obligation, end of year 341 329 908 798 36 37 Plan assets: Fair value of plan assets, 229 198 359 336 0 0 Actual return on plan assets 16 9 61 24 0 0 Employer contributions 32 25 47 17 2 2 Benefits and expenses paid (14 ) (8 ) (19 ) (18 ) (2 ) (2 ) Effect of foreign exchange 7 5 0 0 0 0 Fair value of plan assets, end of year 270 229 448 359 0 0 Funded status of the plans (1) $ (71 ) $ (100 ) $ (460 ) $ (439 ) $ (36 ) $ (37 ) Amounts recognized in accumulated other Net actuarial (gain) loss $ 44 $ 67 $ 203 $ 189 $ 6 $ 7 Prior service (credit) cost (2 ) (2 ) (4 ) (4 ) 0 0 Total included in accumulated $ 42 $ 65 $ 199 $ 185 $ 6 $ 7 Accumulated benefit obligation $ 307 $ 288 $ 756 $ 670 N/A (2) N/A (2) (1) Recognized in other liabilities in the consolidated balance sheets (2) Not applicable
Schedule of Assumptions Used	Pension Benefits Other Japan U.S. Postretirement Benefits 2017 2016 2015 2017 2016 2015 2017 2016 2015 Weighted-average actuarial assumptions: Discount rate - net periodic benefit cost 1.25 % 1.75 % 1.75 % 4.25 % 4.50 % 4.50 % 4.25 % 4.50 % 4.50 % Discount rate - benefit obligations 1.25 1.25 1.75 3.75 4.25 4.50 3.75 4.25 4.50 Expected long-term return on plan assets 2.00 2.00 2.00 6.75 7.00 7.25 N/A (1) N/A (1) N/A (1) Rate of compensation increase N/A (1) N/A (1) N/A (1) 4.00 4.00 4.00 N/A (1) N/A (1) N/A (1) Health care cost trend rates N/A (1) N/A (1) N/A (1) N/A (1) N/A (1) N/A (1) 5.40 (2) 5.20 (2) 5.30 (2) (1) Not applicable (2) For the years 2017 , 2016 and 2015 , the health care cost trend rates are expected to trend down to 4.5% in 77 years , 4.5% in 74 years , and 4.5% in 78 years , respectively.
Schedule of Effect of One-Percentage-Point Change in Assumed Health Care Cost Trend Rates	A one-percentage point increase and decrease in assumed health care cost trend rates would have the following effects as of December 31, 2017 : (In millions) One percentage point increase: Increase in total service and interest costs $ 0 Increase in postretirement benefit obligation 2 One percentage point decrease: Decrease in total service and interest costs $ 0 Decrease in postretirement benefit obligation 2
Schedule of Net Benefit Costs	Pension and other postretirement benefit expenses are included in acquisition and operating expenses in the consolidated statements of earnings, which includes $35 million , $17 million and $(5) million of other components of net periodic pension cost and postretirement costs (other than services costs) for the years ended December 31, 2017, 2016 and 2015, respectively. Total net periodic benefit cost includes the following components: Pension Benefits Other Japan U.S. Postretirement Benefits (In millions) 2017 2016 2015 2017 2016 2015 2017 2016 2015 Service cost $ 20 $ 16 $ 15 $ 24 $ 23 $ 23 $ 0 $ 1 $ 1 Interest cost 6 9 1 40 29 18 1 2 2 Expected return on plan (5 ) (4 ) (4 ) (24 ) (23 ) (22 ) 0 0 0 Amortization of net actuarial 2 1 1 14 13 14 1 1 2 Amortization of prior service 0 0 0 0 0 0 0 (11 ) (17 ) Net periodic (benefit) cost $ 23 $ 22 $ 13 $ 54 $ 42 $ 33 $ 2 $ (7 ) $ (12 )
Schedule of Amounts Recognized in Other Comprehensive Income (Loss)	The following table summarizes the amounts recognized in other comprehensive loss (income) for the years ended December 31: Pension Benefits Other Japan U.S. Postretirement Benefits (In millions) 2017 2016 2015 2017 2016 2015 2017 2016 2015 Net actuarial loss (gain) $ (21 ) $ 26 $ 3 $ 28 $ 27 $ 22 $ 0 $ (4 ) $ (5 ) Amortization of net actuarial loss (2 ) (1 ) (1 ) (14 ) (13 ) (14 ) (1 ) (1 ) (2 ) Amortization of prior 0 0 0 0 0 0 0 11 17 Total $ (23 ) $ 25 $ 2 $ 14 $ 14 $ 8 $ (1 ) $ 6 $ 10
Schedule of Expected Benefit Payments	The following table provides expected benefit payments, which reflect expected future service, as appropriate. Pension Benefits Other (In millions) Japan U.S. Postretirement Benefits 2018 $ 10 $ 23 $ 2 2019 11 24 3 2020 12 25 3 2021 12 26 3 2022 18 35 3 2023-2027 82 184 17
Schedule of Allocation of Plan Assets	Asset allocation targets as of December 31, 2017 were as follows: Japan Pension U.S. Pension Domestic equities 11 % 40 % International equities 15 20 Fixed income securities 59 40 Other 15 0 Total 100 % 100 %
Plan Assets
Fair Value, Assets Measured on Recurring Basis	The following table presents the fair value of Aflac Japan's pension plan assets that are measured at fair value on a recurring basis as of December 31. All of these assets are classified as Level 2 in the fair value hierarchy, except cash and cash equivalents which are classified as Level 1. (In millions) 2017 2016 Japan pension plan assets: Equities: Japanese equity securities $ 37 $ 28 International equity securities 50 40 Fixed income securities: Japanese bonds 91 79 International bonds 62 55 Insurance contracts 30 27 Cash and cash equivalents 0 0 Total $ 270 $ 229 The following table presents the fair value of Aflac U.S.'s pension plan assets that are measured at fair value on a recurring basis as of December 31. All of these assets are classified as Level 1 in the fair value hierarchy. (In millions) 2017 2016 U.S. pension plan assets: Mutual funds: Large cap equity funds $ 124 $ 104 Mid cap equity funds 22 19 Real estate equity funds 13 10 International equity funds 108 85 Fixed income bond funds 175 136 Aflac Incorporated common stock 5 4 Cash and cash equivalents 1 1 Total $ 448 $ 359

COMMITMENTS AND CONTINGENT LI43

COMMITMENTS AND CONTINGENT LIABILITIES (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Schedule of Future Minimum Rental Payments for Operating Leases	Future minimum lease payments due under non-cancelable operating leases at December 31, 2017 , were as follows: (In millions) 2018 $ 61 2019 33 2020 24 2021 21 2022 16 Thereafter 30 Total future minimum lease payments $ 185

Unaudited Consolidated Quarte44

Unaudited Consolidated Quarterly Financial Data (Tables)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Schedule of Quarterly Financial Information	In management's opinion, the following quarterly financial information fairly presents the results of operations for such periods and is prepared on a basis consistent with the Company's annual audited financial statements. (In millions, except for per-share amounts) March 31, June 30, September 30, December 31, Net premium income $ 4,638 $ 4,665 $ 4,648 $ 4,580 Net investment income 794 802 811 812 Realized investment gains (losses) (140 ) (56 ) 30 15 Other income (loss) 17 17 17 17 Total revenues 5,309 5,428 5,506 5,424 Total benefits and expenses 4,411 4,383 4,431 4,425 Earnings before income taxes 898 1,045 1,075 999 Total income tax 306 332 359 (1,585 ) Net earnings $ 592 $ 713 $ 716 $ 2,584 Net earnings per basic share $ 1.48 $ 1.80 $ 1.81 $ 6.59 Net earnings per diluted share 1.47 1.79 1.80 6.54 Quarterly amounts may not agree in total to the corresponding annual amounts due to rounding. (In millions, except for per-share amounts) March 31, June 30, September 30, December 31, Net premium income $ 4,602 $ 4,823 $ 5,022 $ 4,778 Net investment income 801 822 842 813 Realized investment gains (losses) 30 (223 ) (164 ) 344 Other income (loss) 18 15 16 20 Total revenues 5,451 5,437 5,716 5,955 Total benefits and expenses 4,334 4,603 4,753 4,802 Earnings before income taxes 1,117 834 963 1,153 Total income tax 386 286 334 402 Net earnings $ 731 $ 548 $ 629 $ 751 Net earnings per basic share $ 1.75 $ 1.33 $ 1.54 $ 1.85 Net earnings per diluted share 1.74 1.32 1.53 1.84 Quarterly amounts may not agree in total to the corresponding annual amounts due to rounding.

SUBSEQUENT EVENTS (Tables)

SUBSEQUENT EVENTS (Tables)	12 Months Ended
	Dec. 31, 2017
Subsequent Events [Abstract]
Pro Forma Earnings Per Diluted Share	Years ended December 31, Unaudited pro forma 2017 2016 2015 Diluted earnings per common share attributable to Aflac Incorporated shareholders, adjusted for the two-for-one stock split $ 5.77 $ 3.21 $ 2.93

SUMMARY OF SIGNIFICANT ACCOUN46

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Summary of Signficant Accounting Policies - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jan. 01, 2018
Aflac Japan
Significant Accounting Policies [Line Items]
Percentage of the Company assets	83.00%	83.00%
Aflac Japan's percentage of the Company's total revenues	70.00%	71.00%	70.00%
Accounting Standards Update 2015-03
Significant Accounting Policies [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Liabilities			$ 40
Upper Limit
Significant Accounting Policies [Line Items]
Estimation of Percent of Leases Within Scope of the Guidance to Total Assets	1.00%
Estimation of Percent of Revenues Within Scope of the Guidance to Total Revenues	1.00%
Scenario, Forecast | Accumulated other comprehensive income (loss) | Accounting Standards Update 2016-01
Significant Accounting Policies [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption				$ (133)
Scenario, Forecast | Retained earnings | Accounting Standards Update 2016-01
Significant Accounting Policies [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption				$ 133

BUSINESS SEGMENT AND FOREIGN 47

BUSINESS SEGMENT AND FOREIGN INFORMATION - Additional Information (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)segment	Dec. 31, 2016USD ($)
Segment Reporting Information [Line Items]
Reportable insurance business segments | segment	2
Total receivables related to Aflac Japan's operations	$ 827	$ 669
Aflac Japan
Segment Reporting Information [Line Items]
Total receivables related to Aflac Japan's operations	$ 334	$ 207
Percentage of total receivables related to Aflac Japan's operations	40.40%	30.90%
Maximum | Machinery and equipment
Segment Reporting Information [Line Items]
Property, Plant and Equipment, Useful Life	20 years
Maximum | Building
Segment Reporting Information [Line Items]
Property, Plant and Equipment, Useful Life	50 years
Maximum | Furniture and fixtures
Segment Reporting Information [Line Items]
Property, Plant and Equipment, Useful Life	20 years

BUSINESS SEGMENT AND FOREIGN 48

BUSINESS SEGMENT AND FOREIGN INFORMATION - Operations by Segment - Revenues (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting, Revenue Reconciling Item [Line Items]
Premiums Earned, Net		$ 4,580	$ 4,648	$ 4,665	$ 4,638	$ 4,778	$ 5,022	$ 4,823	$ 4,602	$ 18,531	$ 19,225	$ 17,570
Net investment income		812	811	802	794	813	842	822	801	3,220	3,278	3,135
Total revenues		$ 5,424	$ 5,506	$ 5,428	$ 5,309	$ 5,955	$ 5,716	$ 5,437	$ 5,451	21,667	22,559	20,872
Total Operating Revenues										21,667	22,472	20,778
Realized investment gains (losses), non-operating	[1],[2],[3],[4]									0	87	94
Gain (loss) on change in fair value of derivative, interest rate component, operating										77	85	85
Life insurance
Segment Reporting, Revenue Reconciling Item [Line Items]
Premiums Earned, Net										4,034	4,740	4,289
Aflac Japan
Segment Reporting, Revenue Reconciling Item [Line Items]
Premiums Earned, Net										12,752	13,537	12,046
Net investment income, less amortized hedge costs	[1]									2,235	2,368	2,364
Net investment income										2,463	2,554	2,436
Other income (loss)										41	40	31
Total revenues										15,028	15,945	14,441
Hedge cost										(228)	(186)	(72)
Aflac Japan | Cancer
Segment Reporting, Revenue Reconciling Item [Line Items]
Premiums Earned, Net										5,612	5,639	4,933
Aflac Japan | Medical and other health
Segment Reporting, Revenue Reconciling Item [Line Items]
Premiums Earned, Net										3,379	3,429	3,092
Aflac Japan | Life insurance
Segment Reporting, Revenue Reconciling Item [Line Items]
Premiums Earned, Net										3,761	4,469	4,021
Aflac U.S.
Segment Reporting, Revenue Reconciling Item [Line Items]
Premiums Earned, Net										5,563	5,454	5,347
Net investment income										721	703	678
Other income (loss)										5	10	8
Total revenues										6,289	6,167	6,033
Aflac U.S. | Cancer
Segment Reporting, Revenue Reconciling Item [Line Items]
Premiums Earned, Net										1,308	1,299	1,293
Aflac U.S. | Life insurance
Segment Reporting, Revenue Reconciling Item [Line Items]
Premiums Earned, Net										273	271	268
Aflac U.S. | Accident and disability
Segment Reporting, Revenue Reconciling Item [Line Items]
Premiums Earned, Net										2,537	2,469	2,391
Aflac U.S. | Other health
Segment Reporting, Revenue Reconciling Item [Line Items]
Premiums Earned, Net										1,445	1,415	1,395
Other business segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total revenues										140	275	225
Total Business Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total revenues										21,457	22,387	20,699
Corporate and eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Total revenues										$ 210	$ 85	$ 79
[1]	Amortized hedge costs related to hedging U.S. dollar-denominated investments held in Aflac Japan were $228, $186 and $72 for 2017, 2016 and 2015 respectively, and have been reclassified from realized investment gains (losses) and reported as a deduction from pretax operating earnings when analyzing segment operations to conform to current year reporting.
[2]	Excluding a gain of $77 in 2017 and $85 in both 2016 and 2015 related to the interest rate component of the change in fair value of foreign currency swaps on notes payable which is classified as an operating gain when analyzing segment operations
[3]	Prior year foreign currency transaction gains and losses have been reclassified from other non-operating income (loss) to realized investment gains (losses) to conform to current-year reporting classifications. These reclassifications had no impact on total earnings before income taxes.
[4]	Prior year foreign currency transaction gains and losses have been reclassified from other non-operating income (loss) to realized investment gains (losses) to conform to current-year reporting classifications. These reclassifications had no impact on total revenues.

BUSINESS SEGMENT AND FOREIGN 49

BUSINESS SEGMENT AND FOREIGN INFORMATION - Operations by Segment - Pretax Earnings (Details) - USD ($) $ in Millions		1 Months Ended	3 Months Ended								12 Months Ended
		Nov. 30, 2017	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Pretax operating earnings											$ 4,087	$ 4,117	$ 4,001
Realized investment gains (losses), non-operating	[1],[2],[3],[4]										0	87	94
Other non-operating income (loss)	[3],[5]										(69)	(137)	(233)
Earnings before income taxes			$ 999	$ 1,075	$ 1,045	$ 898	$ 1,153	$ 963	$ 834	$ 1,117	4,018	4,067	3,862
Income taxes applicable to pretax operating earnings											1,370	1,426	1,377
Effect of foreign currency translation on after tax operating earnings											(41)	141	(198)
Gain (loss) on change in fair value of derivative, interest rate component, operating											77	85	85
Aflac Japan
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Hedge cost											228	186	72
Pretax operating earnings	[1]										3,054	3,148	3,103
Aflac U.S.
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Pretax operating earnings											1,245	1,208	1,101
Other business segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Pretax operating earnings											11	18	14
Total Business Segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Pretax operating earnings											4,310	4,374	4,218
Interest expense, noninsurance operations
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Pretax operating earnings											(122)	(128)	(146)
Corporate and eliminations
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Pretax operating earnings											(101)	(129)	(71)
5.50% subordinated notes due September 2052
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Expense on extinguishment of debt		$ 13									$ 13
Senior Notes due 2039 and 2040
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Expense on extinguishment of debt												$ 137
8.50% senior notes due May 2019
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Expense on extinguishment of debt													$ 230
[1]	Amortized hedge costs related to hedging U.S. dollar-denominated investments held in Aflac Japan were $228, $186 and $72 for 2017, 2016 and 2015 respectively, and have been reclassified from realized investment gains (losses) and reported as a deduction from pretax operating earnings when analyzing segment operations to conform to current year reporting.
[2]	Excluding a gain of $77 in 2017 and $85 in both 2016 and 2015 related to the interest rate component of the change in fair value of foreign currency swaps on notes payable which is classified as an operating gain when analyzing segment operations
[3]	Prior year foreign currency transaction gains and losses have been reclassified from other non-operating income (loss) to realized investment gains (losses) to conform to current-year reporting classifications. These reclassifications had no impact on total earnings before income taxes.
[4]	Prior year foreign currency transaction gains and losses have been reclassified from other non-operating income (loss) to realized investment gains (losses) to conform to current-year reporting classifications. These reclassifications had no impact on total revenues.
[5]	Includes expense of $13 in 2017, $137 in 2016 and $230 in 2015 for the early extinguishment of debt

BUSINESS SEGMENT AND FOREIGN 50

BUSINESS SEGMENT AND FOREIGN INFORMATION - Operations by Segment - Assets (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 137,217	$ 129,819	$ 118,256
Aflac Japan
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	114,402	107,858	97,646
Aflac U.S.
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	19,893	19,453	18,537
Other business segments
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	547	270	188
Total Business Segments
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	134,842	127,581	116,371
Corporate and eliminations
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 2,375	$ 2,238	$ 1,885

BUSINESS SEGMENT AND FOREIGN 51

BUSINESS SEGMENT AND FOREIGN INFORMATION - Yen/Dollar Exchange Rates Used (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)¥ / $	Dec. 31, 2016USD ($)¥ / $	Dec. 31, 2015USD ($)¥ / $
Segment Reporting, Other Significant Reconciling Item [Line Items]
Weighted-average yen/dollar exchange rate | ¥ / $	112.16	108.70	120.99
Yen percent strengthening (weakening)	(3.10%)	11.30%	(12.80%)
Exchange effect on pretax operating earnings (in millions)	$ (63)	$ 218	$ (288)
Yen/dollar exchange rate at December 31 | ¥ / $	113	116.49
Yen percent strengthening (weakening)	3.10%	3.50%
Exchange effect on total assets
Segment Reporting, Other Significant Reconciling Item [Line Items]
Exchange effect	$ 2,593	$ 2,820
Exchange effect on total liabilities
Segment Reporting, Other Significant Reconciling Item [Line Items]
Exchange effect	$ 2,848	$ 3,109

BUSINESS SEGMENT AND FOREIGN 52

BUSINESS SEGMENT AND FOREIGN INFORMATION - Information on Transfers of Funds from Aflac Japan (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting [Abstract]
Management fees	$ 93	$ 79	$ 53
Allocated expenses	109	106	101
Profit repatriation	1,150	1,286	2,139
Total transfers from Aflac Japan	$ 1,352	$ 1,471	$ 2,293

BUSINESS SEGMENT AND FOREIGN 53

BUSINESS SEGMENT AND FOREIGN INFORMATION - Classes of Property and Equipment (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Property and equipment:
Land	$ 168	$ 166
Buildings	441	421
Equipment	372	355
Total property and equipment	981	942
Less accumulated depreciation	547	509
Net property and equipment	$ 434	$ 433

INVESTMENTS - Components of Net

INVESTMENTS - Components of Net Investment Income (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income									$ 3,334	$ 3,385	$ 3,230
Less investment expenses									114	107	95
Net investment income	$ 812	$ 811	$ 802	$ 794	$ 813	$ 842	$ 822	$ 801	3,220	3,278	3,135
Fixed-maturity securities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income									3,094	3,214	3,094
Perpetual securities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income									79	94	114
Equity securities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income									42	35	3
Other Investments
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income									94	31	15
Short term investments and cash equivalents
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income									$ 25	$ 11	$ 4

INVESTMENTS - Available-For-Sal

INVESTMENTS - Available-For-Sale Investments in Debt Securities, Perpetual Securities and Equity Securities (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	$ 75,978	$ 69,072
Gross Unrealized Gains	10,165	8,722
Gross Unrealized Losses	807	1,092
Fair Value	85,336	76,702
Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	73,670	66,363
Gross Unrealized Gains	9,631	8,432
Gross Unrealized Losses	777	1,035
Fair Value	82,524	73,760
Perpetual securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	1,462	1,506
Gross Unrealized Gains	354	176
Gross Unrealized Losses	27	49
Fair Value	1,789	1,633
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	846	1,203
Gross Unrealized Gains	180	114
Gross Unrealized Losses	3	8
Fair Value	1,023	1,309
Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	38,962	32,459
Gross Unrealized Gains	5,257	4,951
Gross Unrealized Losses	323	261
Fair Value	43,896	37,149
Yen-denominated | Equity securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	561	624
Gross Unrealized Gains	135	83
Gross Unrealized Losses	1	2
Fair Value	695	705
Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	34,708	33,904
Gross Unrealized Gains	4,374	3,481
Gross Unrealized Losses	454	774
Fair Value	38,628	36,611
Dollar-denominated | Equity securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	285	579
Gross Unrealized Gains	45	31
Gross Unrealized Losses	2	6
Fair Value	328	604
Japan government and agencies | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	27,980	22,857
Gross Unrealized Gains	3,363	3,359
Gross Unrealized Losses	271	160
Fair Value	31,072	26,056
Municipalities | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	1,370	1,295
Municipalities | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	314	246
Gross Unrealized Gains	28	29
Gross Unrealized Losses	12	8
Fair Value	330	267
Municipalities | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	872	894
Gross Unrealized Gains	168	142
Gross Unrealized Losses	0	8
Fair Value	1,040	1,028
Mortgage- and asset-backed securities | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	444	1,337
Mortgage- and asset-backed securities | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	242	1,096
Gross Unrealized Gains	29	33
Gross Unrealized Losses	0	8
Fair Value	271	1,121
Mortgage- and asset-backed securities | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	161	196
Gross Unrealized Gains	12	20
Gross Unrealized Losses	0	0
Fair Value	173	216
Public utilities | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	7,954	7,683
Public utilities | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	1,635	1,533
Gross Unrealized Gains	352	318
Gross Unrealized Losses	6	3
Fair Value	1,981	1,848
Public utilities | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	5,116	5,205
Gross Unrealized Gains	884	690
Gross Unrealized Losses	27	60
Fair Value	5,973	5,835
Sovereign and supranational | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	1,909	1,469
Sovereign and supranational | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	1,380	862
Gross Unrealized Gains	190	186
Gross Unrealized Losses	1	5
Fair Value	1,569	1,043
Sovereign and supranational | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	267	335
Gross Unrealized Gains	73	91
Gross Unrealized Losses	0	0
Fair Value	340	426
Banks/financial institutions | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	7,377	6,063
Banks/financial institutions | Perpetual securities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	1,556	1,420
Banks/financial institutions | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	3,521	2,673
Gross Unrealized Gains	524	403
Gross Unrealized Losses	26	74
Fair Value	4,019	3,002
Banks/financial institutions | Yen-denominated | Perpetual securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	1,221	1,266
Gross Unrealized Gains	287	128
Gross Unrealized Losses	27	49
Fair Value	1,481	1,345
Banks/financial institutions | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	2,762	2,570
Gross Unrealized Gains	604	507
Gross Unrealized Losses	8	16
Fair Value	3,358	3,061
Banks/financial institutions | Dollar-denominated | Perpetual securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	46	51
Gross Unrealized Gains	29	24
Gross Unrealized Losses	0	0
Fair Value	75	75
Other corporate | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	32,240	29,699
Other corporate | Perpetual securities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	233	213
Other corporate | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	3,890	3,192
Gross Unrealized Gains	771	623
Gross Unrealized Losses	7	3
Fair Value	4,654	3,812
Other corporate | Yen-denominated | Perpetual securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	195	189
Gross Unrealized Gains	38	24
Gross Unrealized Losses	0	0
Fair Value	233	213
Other corporate | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	25,384	24,556
Gross Unrealized Gains	2,620	2,021
Gross Unrealized Losses	418	690
Fair Value	27,586	25,887
U.S. Government and Agencies | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	146	148
Gross Unrealized Gains	13	10
Gross Unrealized Losses	1	0
Fair Value	$ 158	$ 158

INVESTMENTS - Held-to-Maturity

INVESTMENTS - Held-to-Maturity Investments in Debt Securities (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	$ 31,430	$ 33,350
Gross Unrealized Gains	6,651	6,735
Gross Unrealized Losses	9	64
Fair Value	38,072	40,021
Fixed maturities
Schedule of Held-to-maturity Securities [Line Items]
Fair Value	38,072	40,021
Yen-denominated | Fixed maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	31,430	33,350
Gross Unrealized Gains	6,651	6,735
Gross Unrealized Losses	9	64
Fair Value	38,072	40,021
Japan government and agencies | Yen-denominated | Fixed maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	21,331
Gross Unrealized Gains	5,160	5,338
Gross Unrealized Losses	0	0
Fair Value	26,491	26,040
Municipalities | Fixed maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	357	350
Fair Value	462	457
Municipalities | Yen-denominated | Fixed maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	357
Gross Unrealized Gains	105	107
Gross Unrealized Losses	0	0
Fair Value	462	457
Mortgage- and asset-backed securities | Fixed maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	26	30
Fair Value	27	32
Mortgage- and asset-backed securities | Yen-denominated | Fixed maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	26
Gross Unrealized Gains	1	2
Gross Unrealized Losses	0	0
Fair Value	27	32
Public utilities | Fixed maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	3,300	3,201
Fair Value	3,698	3,536
Public utilities | Yen-denominated | Fixed maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	3,300
Gross Unrealized Gains	398	358
Gross Unrealized Losses	0	23
Fair Value	3,698	3,536
Sovereign and supranational | Fixed maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	1,523	2,602
Fair Value	1,835	2,877
Sovereign and supranational | Yen-denominated | Fixed maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	1,523
Gross Unrealized Gains	312	283
Gross Unrealized Losses	0	8
Fair Value	1,835	2,877
Banks/financial institutions | Fixed maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	2,206	3,731
Fair Value	2,387	3,900
Banks/financial institutions | Yen-denominated | Fixed maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	2,206
Gross Unrealized Gains	190	195
Gross Unrealized Losses	9	26
Fair Value	2,387	3,900
Other corporate | Fixed maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	2,687	2,734
Fair Value	3,172	3,179
Other corporate | Yen-denominated | Fixed maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	2,687
Gross Unrealized Gains	485	452
Gross Unrealized Losses	0	7
Fair Value	$ 3,172	$ 3,179

INVESTMENTS - Additional Inform

INVESTMENTS - Additional Information (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)investment	Dec. 31, 2016USD ($)investment	Dec. 31, 2015investment
Schedule of Investments [Line Items]
Reclassified investments from the held-to-maturity portfolio to the available-for-sale portfolio, number of investments | investment	3	0	0
Reclassified investments from the held-to-maturity portfolio to the available-for-sale portfolio, amortized cost	$ 773
Reclassified investments from the held-to-maturity portfolio to the available-for-sale portfolio, aggregate unrealized gain (loss)	47
Allowance for loan loss	11	$ 3
Transitional real estate loan commitments	254
Commercial mortgage loan commitments	13
Middle market loan program unfunded amount	109	$ 91
Middle market loan commitments	552
Limited partnerships investment commitments	$ 888
Percentage that the lending policy requires that the fair value of the securities and/or unrestricted cash received as collateral be of the fair value of the loaned securities	102.00%
Fair value of debt securities on deposit with regulatory authorities in the United States and Japan	$ 21
Parent Company and Other Business Segments
Schedule of Investments [Line Items]
Securities available for sale, fixed maturities, amortized cost	1,300
Securities available for sale, fixed maturities, fair value	$ 1,400

INVESTMENTS - Contractual Matur

INVESTMENTS - Contractual Maturities of Investments in Fixed Maturities (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Held to maturity:
Total fixed maturities held to maturity, amortized cost	$ 31,430	$ 33,350
Held to maturity:
Total fixed maturities held to maturity, fair value	38,072	$ 40,021
Aflac Japan
Available for sale:
Due in one year or less	234
Due after one year through five years	7,155
Due after five years through 10 years	7,812
Due after 10 years	45,028
Mortgage- and asset-backed securities	283
Total fixed maturities available for sale, amortized cost	60,512
Held to maturity:
Due in one year or less	885
Due after one year through five years	434
Due after five years through 10 years	1,634
Due after 10 years	28,451
Mortgage- and asset-backed securities	26
Total fixed maturities held to maturity, amortized cost	31,430
Available for sale:
Due in one year or less	243
Due after one year through five years	7,391
Due after five years through 10 years	8,385
Due after 10 years	51,269
Mortgage- and asset-backed securities	322
Total fixed maturities available for sale, fair value	67,610
Held to maturity:
Due in one year or less	903
Due after one year through five years	455
Due after five years through 10 years	1,802
Due after 10 years	34,885
Mortgage- and asset-backed securities	27
Total fixed maturities held to maturity, fair value	38,072
Aflac U.S.
Available for sale:
Due in one year or less	86
Due after one year through five years	508
Due after five years through 10 years	2,726
Due after 10 years	8,482
Mortgage- and asset-backed securities	40
Total fixed maturities available for sale, amortized cost	11,842
Held to maturity:
Due in one year or less	0
Due after one year through five years	0
Due after five years through 10 years	0
Due after 10 years	0
Mortgage- and asset-backed securities	0
Total fixed maturities held to maturity, amortized cost	0
Available for sale:
Due in one year or less	89
Due after one year through five years	542
Due after five years through 10 years	2,946
Due after 10 years	9,927
Mortgage- and asset-backed securities	41
Total fixed maturities available for sale, fair value	13,545
Held to maturity:
Due in one year or less	0
Due after one year through five years	0
Due after five years through 10 years	0
Due after 10 years	0
Mortgage- and asset-backed securities	0
Total fixed maturities held to maturity, fair value	$ 0

INVESTMENTS - Economic Maturiti

INVESTMENTS - Economic Maturities of Investments in Perpetual Securities (Detail) $ in Millions	Dec. 31, 2017USD ($)
Aflac Japan
Investments Classified by Economic Maturity Date [Line Items]
Due after one year through five years	$ 194
Due after 10 years	1,229
Total perpetual securities available for sale	1,423
Due after one year through five years	233
Due after 10 years	1,495
Total perpetual securities available for sale	1,728
Aflac U.S.
Investments Classified by Economic Maturity Date [Line Items]
Due after one year through five years	0
Due after 10 years	39
Total perpetual securities available for sale	39
Due after one year through five years	0
Due after 10 years	61
Total perpetual securities available for sale	$ 61

INVESTMENTS - Investment Exposu

INVESTMENTS - Investment Exposures Individually Exceeded Ten Percent of Shareholders' Equity (Detail) - Japan National Government - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Summary of Investment Holdings [Line Items]
Credit Rating		A	A
Amortized Cost	[1]	$ 48,399	$ 42,931
Fair Value	[1]	$ 56,532	$ 51,345
[1]	Japan Government Bonds (JGBs) or JGB-backed securities

INVESTMENTS - Information Regar

INVESTMENTS - Information Regarding Pretax Realized Gains and Losses From Investments (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Gain (Loss) on Investments [Line Items]
Other-than-temporary impairment losses realized	$ (37)	$ (85)	$ (154)
Loan loss reserves	(8)	(2)	(1)
Derivative gains (losses)	(109)	(255)	(10)
Foreign currency transaction gain (loss), realized	(33)	186	(32)
Total realized investment gains (losses)	(151)	(14)	106
Equity securities
Gain (Loss) on Investments [Line Items]
Gross gains from sales	104	0	0
Gross losses from sales	(11)	0	0
Net gains (losses) from redemptions	0	22	0
Other-than-temporary impairment losses realized	(22)	(57)	(1)
Total realized investment gains (losses)	71	(35)	(1)
Derivatives and other
Gain (Loss) on Investments [Line Items]
Total realized investment gains (losses)	(142)	(70)	(42)
Available-for-sale securities | Fixed maturities
Gain (Loss) on Investments [Line Items]
Gross gains from sales	36	77	224
Gross losses from sales	(82)	(134)	(8)
Net gains (losses) from redemptions	(23)	112	51
Other-than-temporary impairment losses realized	(7)	(24)	(152)
Total realized investment gains (losses)	(76)	31	115
Available-for-sale securities | Perpetual securities
Gain (Loss) on Investments [Line Items]
Net gains (losses) from redemptions	4	64	35
Other-than-temporary impairment losses realized	0	(2)	0
Total realized investment gains (losses)	$ 4	$ 62	$ 35

INVESTMENTS - Information Reg62

INVESTMENTS - Information Regarding Changes in Unrealized Gains and Losses from Investments (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Changes in unrealized gains (losses):
Changes in unrealized gains (losses)	$ 1,728	$ 2,799	$ (2,595)
Fixed maturities | Available-for-sale securities
Changes in unrealized gains (losses):
Changes in unrealized gains (losses)	1,457	2,690	(2,481)
Perpetual securities | Available-for-sale securities
Changes in unrealized gains (losses):
Changes in unrealized gains (losses)	200	21	(123)
Equity securities
Changes in unrealized gains (losses):
Changes in unrealized gains (losses)	$ 71	$ 88	$ 9

INVESTMENTS - Net Effect on Sha

INVESTMENTS - Net Effect on Shareholders' Equity of Unrealized Gains and Losses from Investment Securities (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Investments [Abstract]
Unrealized Gain (Losses) on Available-for-sale Securities	$ 9,358	$ 7,630
Deferred income taxes	(3,394)	(2,825)
Shareholders' equity, unrealized gains (losses) on investment securities	$ 5,964	$ 4,805

INVESTMENTS - Fair Value and Gr

INVESTMENTS - Fair Value and Gross Unrealized Losses for Securities That Have Been in Continuous Unrealized Loss Position (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	$ 16,766	$ 20,275
Total Unrealized Losses	816	1,156
Less Than 12 months Fair Value	5,836	14,743
Less Than 12 months Unrealized Losses	78	621
12 months or longer Fair Value	10,930	5,532
12 months or longer Unrealized Losses	738	535
Fixed maturities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	16,340	19,536
Total Unrealized Losses	786	1,099
Less Than 12 months Fair Value	5,776	14,398
Less Than 12 months Unrealized Losses	77	612
12 months or longer Fair Value	10,564	5,138
12 months or longer Unrealized Losses	709	487
Perpetual securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	345	479
Total Unrealized Losses	27	49
Less Than 12 months Fair Value	0	85
Less Than 12 months Unrealized Losses	0	1
12 months or longer Fair Value	345	394
12 months or longer Unrealized Losses	27	48
Equity securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	81	260
Total Unrealized Losses	3	8
Less Than 12 months Fair Value	60	260
Less Than 12 months Unrealized Losses	1	8
12 months or longer Fair Value	21	0
12 months or longer Unrealized Losses	2	0
Dollar-denominated | Fixed maturities | U.S. Government and Agencies
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	74
Total Unrealized Losses	1
Less Than 12 months Fair Value	74
Less Than 12 months Unrealized Losses	1
12 months or longer Fair Value	0
12 months or longer Unrealized Losses	0
Dollar-denominated | Fixed maturities | Municipalities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value		44
Total Unrealized Losses		8
Less Than 12 months Fair Value		0
Less Than 12 months Unrealized Losses		0
12 months or longer Fair Value		44
12 months or longer Unrealized Losses		8
Dollar-denominated | Fixed maturities | Public utilities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	785	1,265
Total Unrealized Losses	27	60
Less Than 12 months Fair Value	221	790
Less Than 12 months Unrealized Losses	3	32
12 months or longer Fair Value	564	475
12 months or longer Unrealized Losses	24	28
Dollar-denominated | Fixed maturities | Banks/financial institutions
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	362	268
Total Unrealized Losses	8	16
Less Than 12 months Fair Value	316	238
Less Than 12 months Unrealized Losses	5	10
12 months or longer Fair Value	46	30
12 months or longer Unrealized Losses	3	6
Dollar-denominated | Fixed maturities | Other corporate
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	7,741	10,462
Total Unrealized Losses	418	690
Less Than 12 months Fair Value	2,839	7,252
Less Than 12 months Unrealized Losses	50	346
12 months or longer Fair Value	4,902	3,210
12 months or longer Unrealized Losses	368	344
Dollar-denominated | Equity securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	41	211
Total Unrealized Losses	2	6
Less Than 12 months Fair Value	21	211
Less Than 12 months Unrealized Losses	0	6
12 months or longer Fair Value	20	0
12 months or longer Unrealized Losses	2	0
Yen-denominated | Fixed maturities | Japan government and agencies
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	5,255	3,958
Total Unrealized Losses	271	160
Less Than 12 months Fair Value	1,264	3,958
Less Than 12 months Unrealized Losses	9	160
12 months or longer Fair Value	3,991	0
12 months or longer Unrealized Losses	262	0
Yen-denominated | Fixed maturities | Municipalities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	129	105
Total Unrealized Losses	12	8
Less Than 12 months Fair Value	10	105
Less Than 12 months Unrealized Losses	0	8
12 months or longer Fair Value	119	0
12 months or longer Unrealized Losses	12	0
Yen-denominated | Fixed maturities | Mortgage- and asset-backed securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value		713
Total Unrealized Losses		8
Less Than 12 months Fair Value		713
Less Than 12 months Unrealized Losses		8
12 months or longer Fair Value		0
12 months or longer Unrealized Losses		0
Yen-denominated | Fixed maturities | Public utilities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	83	635
Total Unrealized Losses	6	26
Less Than 12 months Fair Value	0	347
Less Than 12 months Unrealized Losses	0	14
12 months or longer Fair Value	83	288
12 months or longer Unrealized Losses	6	12
Yen-denominated | Fixed maturities | Sovereign and supranational
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	309	244
Total Unrealized Losses	1	13
Less Than 12 months Fair Value	309	38
Less Than 12 months Unrealized Losses	1	5
12 months or longer Fair Value	0	206
12 months or longer Unrealized Losses	0	8
Yen-denominated | Fixed maturities | Banks/financial institutions
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	1,162	1,521
Total Unrealized Losses	35	100
Less Than 12 months Fair Value	394	636
Less Than 12 months Unrealized Losses	4	19
12 months or longer Fair Value	768	885
12 months or longer Unrealized Losses	31	81
Yen-denominated | Fixed maturities | Other corporate
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	440	321
Total Unrealized Losses	7	10
Less Than 12 months Fair Value	349	321
Less Than 12 months Unrealized Losses	4	10
12 months or longer Fair Value	91	0
12 months or longer Unrealized Losses	3	0
Yen-denominated | Perpetual securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	345	479
Total Unrealized Losses	27	49
Less Than 12 months Fair Value	0	85
Less Than 12 months Unrealized Losses	0	1
12 months or longer Fair Value	345	394
12 months or longer Unrealized Losses	27	48
Yen-denominated | Equity securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	40	49
Total Unrealized Losses	1	2
Less Than 12 months Fair Value	39	49
Less Than 12 months Unrealized Losses	1	2
12 months or longer Fair Value	1	0
12 months or longer Unrealized Losses	$ 0	$ 0

INVESTMENTS - Other Investments

INVESTMENTS - Other Investments (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Investment [Line Items]
Other investments	[1]	$ 3,402	$ 1,450
Transitional real estate loans
Investment [Line Items]
Other investments		1,235	0
Commercial mortgage loans
Investment [Line Items]
Other investments		908	855
Middle market loans
Investment [Line Items]
Other investments		859	319
Policy loans
Investment [Line Items]
Other investments		210	184
Short-term investments
Investment [Line Items]
Other investments		57	89
Other Investments
Investment [Line Items]
Other investments		$ 133	$ 3
[1]	Includes $2,341 in 2017 and $819 in 2016 of loan receivables and limited partnerships from consolidated variable interest entities

INVESTMENTS - Investments in Co

INVESTMENTS - Investments in Consolidated Variable Interest Entities (Detail) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Other investments, amortized cost	[1]	$ 3,402	$ 1,450
Asset derivatives		331	1,207
Assets, fair value		89,215	83,044
Liability derivatives, fair value		474	1,998
Liabilities, amortized cost		112,619	109,337
Liabilities, fair value disclosure		474	1,998
Variable Interest Entity, Consolidated
Variable Interest Entity [Line Items]
Securities available for sale, fixed maturities, amortized cost		4,300	4,168
Securities available for sale, fixed maturities, fair value		5,294	4,982
Securities available for sale, perpetual securities, amortized cost		238	237
Securities available for sale, perpetual securities, fair value		215	208
Securities available for sale, equity securities, cost		606	972
Securities available for sale, equity securities, fair value		753	1,044
Other investments, amortized cost	[2]	2,341	819
Other investments, fair value disclosure	[2]	2,328	789
Asset derivatives, amortized cost	[3]	151	127
Asset derivatives	[3]	151	127
Assets, amortized cost		7,636	6,323
Assets, fair value		8,741	7,150
Liability derivatives, amortized cost	[3]	128	146
Liability derivatives, fair value	[3]	128	146
Liabilities, amortized cost		128	146
Liabilities, fair value disclosure		$ 128	$ 146
[1]	Includes $2,341 in 2017 and $819 in 2016 of loan receivables and limited partnerships from consolidated variable interest entities
[2]	Consists of TREs, CMLs, MMLs, and alternative investments in limited partnerships
[3]	Consists entirely of derivatives

INVESTMENTS - Investments in Va

INVESTMENTS - Investments in Variable Interest Entities Not Consolidated (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Securities held to maturity, fixed maturities, amortized cost		$ 31,430	$ 33,350
Securities held to maturity, fixed maturities, fair value		38,072	40,021
Other investments, amortized cost	[1]	3,402	1,450
Assets, fair value		89,215	83,044
Variable Interest Entity, Not Consolidated
Variable Interest Entity [Line Items]
Securities available for sale, fixed maturities, amortized cost		4,827	4,729
Securities available for sale, fixed maturities, fair value		5,506	5,261
Securities available for sale, perpetual securities, amortized cost		177	172
Securities available for sale, perpetual securities, fair value		218	200
Securities held to maturity, fixed maturities, amortized cost		2,549	2,563
Securities held to maturity, fixed maturities, fair value		2,929	2,948
Other investments, amortized cost		55	1
Other investments, fair value disclosure		55	1
Assets, amortized cost		7,608	7,465
Assets, fair value		$ 8,708	$ 8,410
[1]	Includes $2,341 in 2017 and $819 in 2016 of loan receivables and limited partnerships from consolidated variable interest entities

INVESTMENTS - Securities Lendin

INVESTMENTS - Securities Lending Accounted for as Secured Borrowings (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending transactions		$ 606	$ 526
Gross amount of recognized liabilities for securities lending		606	526
Amounts related to agreements not included in offsetting disclosure in Note 4		0	0
Japan government and agencies
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending transactions		49
Public utilities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending transactions		73	62
Banks/financial institutions
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending transactions		54	34
Other corporate
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending transactions		415	430
Equity securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending transactions		15
Maturity Overnight and Continuous
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending transactions	[1]	557	526
Maturity Overnight and Continuous | Japan government and agencies
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending transactions	[1]	0
Maturity Overnight and Continuous | Public utilities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending transactions	[1]	73	62
Maturity Overnight and Continuous | Banks/financial institutions
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending transactions	[1]	54	34
Maturity Overnight and Continuous | Other corporate
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending transactions	[1]	415	430
Maturity Overnight and Continuous | Equity securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending transactions	[1]	15
Maturity up to 30 Days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending transactions		49	0
Maturity up to 30 Days | Japan government and agencies
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending transactions		49
Maturity up to 30 Days | Public utilities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending transactions		0	0
Maturity up to 30 Days | Banks/financial institutions
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending transactions		0	0
Maturity up to 30 Days | Other corporate
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending transactions		0	$ 0
Maturity up to 30 Days | Equity securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending transactions		$ 0
[1]	These securities are pledged as collateral under the Company's U.S. securities lending program and can be called at its discretion; therefore, they are classified as Overnight and Continuous.

DERIVATIVE INSTRUMENTS - Additi

DERIVATIVE INSTRUMENTS - Additional Information (Detail) ¥ in Billions	12 Months Ended
	Dec. 31, 2017USD ($)yrcounterparties	Dec. 31, 2016USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2017JPY (¥)yrcounterparties	Mar. 31, 2015USD ($)	Nov. 30, 2014USD ($)	Jun. 30, 2013USD ($)	Feb. 29, 2012USD ($)
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Hedging activity, weighted-average period (in years) | yr	9			9
Net Derivatives Notional Amount	$ 25,751,000,000	$ 43,927,000,000
Number of counterparties | counterparties	15			15
Number of counterparties that comprise majority of aggregate notional amount of swaps | counterparties	4			4
Percentage of notional amount of swaps from certain number of counterparties	60.00%			60.00%
Derivative, Net Liability Position, Aggregate Fair Value	$ 264,000,000	1,200,000,000
Additional Collateral, Aggregate Fair Value	9,000,000
Cash flow hedges
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Net Derivatives Notional Amount	75,000,000	75,000,000
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	0	0	$ 0
Net investment hedge
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Net Derivatives Notional Amount	439,000,000	1,052,000,000
Net investment hedge gain loss reclassified to earnings net	0	0	$ 0
Net investment hedge | Foreign currency forwards
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Net Derivatives Notional Amount	5,000,000	$ 209,000,000
2.40% senior notes due March 2020
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Debt instrument, principal amount	550,000,000				$ 550,000,000
4.00% senior notes due February 2022
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Debt instrument, principal amount	350,000,000							$ 350,000,000
3.625% senior notes due June 2023
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Debt instrument, principal amount	700,000,000						$ 700,000,000
3.625% senior notes due November 2024
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Debt instrument, principal amount	750,000,000					$ 750,000,000
3.25% senior notes due March 2025
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Debt instrument, principal amount	$ 450,000,000				$ 450,000,000
Twenty Seventeen profit repatriation | Foreign currency forwards and options
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Net Derivatives Notional Amount | ¥				¥ 90.9
Future profit repatriation | Foreign currency forwards and options
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Net Derivatives Notional Amount | ¥				¥ 49.5

DERIVATIVE INSTRUMENTS - Summar

DERIVATIVE INSTRUMENTS - Summary of Balance Sheet Classification of Derivative Fair Value Amounts, as well as Gross Asset and Liability Fair Value Amounts (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Net Derivatives Notional Amount	$ 25,751	$ 43,927
Derivative asset, fair value, gross asset including not subject to master netting arrangement	331	1,207
Derivative liability, fair value, gross liability including not subject to master netting arrangement	(474)	(1,998)
Asset Derivatives Fair Value	180	1,080
Liability Derivatives Fair Value	(346)	(1,852)
Other assets
Derivatives, Fair Value [Line Items]
Net Derivatives Notional Amount	10,948	18,329
Asset Derivatives Fair Value	331	1,207
Liability Derivatives Fair Value	0	0
Other Liabilities
Derivatives, Fair Value [Line Items]
Net Derivatives Notional Amount	14,803	25,598
Asset Derivatives Fair Value	0	0
Liability Derivatives Fair Value	(474)	(1,998)
Cash flow hedges
Derivatives, Fair Value [Line Items]
Net Derivatives Notional Amount	75	75
Asset Derivatives Fair Value	0	0
Liability Derivatives Fair Value	(8)	(10)
Cash flow hedges | Foreign currency swaps
Derivatives, Fair Value [Line Items]
Net Derivatives Notional Amount	75	75
Asset Derivatives Fair Value	0	0
Liability Derivatives Fair Value	(8)	(10)
Fair value hedges
Derivatives, Fair Value [Line Items]
Net Derivatives Notional Amount	15,310	15,189
Asset Derivatives Fair Value	2	2
Liability Derivatives Fair Value	(223)	(791)
Fair value hedges | Foreign currency forwards
Derivatives, Fair Value [Line Items]
Net Derivatives Notional Amount	7,640	10,965
Asset Derivatives Fair Value	2	0
Liability Derivatives Fair Value	(221)	(759)
Fair value hedges | Foreign currency options
Derivatives, Fair Value [Line Items]
Net Derivatives Notional Amount	7,670	4,224
Asset Derivatives Fair Value	0	2
Liability Derivatives Fair Value	(2)	(32)
Net investment hedge
Derivatives, Fair Value [Line Items]
Net Derivatives Notional Amount	439	1,052
Asset Derivatives Fair Value	12	46
Liability Derivatives Fair Value	(1)	(19)
Net investment hedge | Foreign currency forwards
Derivatives, Fair Value [Line Items]
Net Derivatives Notional Amount	5	209
Asset Derivatives Fair Value	0	5
Liability Derivatives Fair Value	0	(2)
Net investment hedge | Foreign currency options
Derivatives, Fair Value [Line Items]
Net Derivatives Notional Amount	434	843
Asset Derivatives Fair Value	12	41
Liability Derivatives Fair Value	(1)	(17)
Non-qualifying strategies
Derivatives, Fair Value [Line Items]
Net Derivatives Notional Amount	9,927	27,611
Asset Derivatives Fair Value	317	1,159
Liability Derivatives Fair Value	(242)	(1,178)
Non-qualifying strategies | Foreign currency swaps
Derivatives, Fair Value [Line Items]
Net Derivatives Notional Amount	5,386	6,266
Asset Derivatives Fair Value	296	490
Liability Derivatives Fair Value	(189)	(220)
Non-qualifying strategies | Foreign currency forwards
Derivatives, Fair Value [Line Items]
Net Derivatives Notional Amount	3,683	21,218
Asset Derivatives Fair Value	20	667
Liability Derivatives Fair Value	(53)	(956)
Non-qualifying strategies | Foreign currency options
Derivatives, Fair Value [Line Items]
Net Derivatives Notional Amount	770	41
Asset Derivatives Fair Value	0	0
Liability Derivatives Fair Value	0	(2)
Non-qualifying strategies | Credit default swaps
Derivatives, Fair Value [Line Items]
Net Derivatives Notional Amount	88	86
Asset Derivatives Fair Value	1	2
Liability Derivatives Fair Value	$ 0	$ 0

DERIVATIVE INSTRUMENTS - Gains

DERIVATIVE INSTRUMENTS - Gains (Losses) Recognized on Fair Value Hedging Relationships (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fixed-maturity securities and equity securities | Foreign currency forwards
Derivative Instruments, Gain (Loss) [Line Items]
Total gains (losses) recognized for derivatives	$ 98	$ 207
Gains (losses) on derivatives excluded from effectiveness testing	(202)	(338)
Gains (losses) on derivatives included in effectiveness testing	300	545
Gains (losses) recognized for hedged items	(278)	(566)
Ineffectiveness recognized for fair value hedge	22	(21)
Fixed maturities | Foreign currency forwards
Derivative Instruments, Gain (Loss) [Line Items]
Total gains (losses) recognized for derivatives			$ (133)
Gains (losses) on derivatives excluded from effectiveness testing			(136)
Gains (losses) on derivatives included in effectiveness testing			3
Gains (losses) recognized for hedged items			(5)
Ineffectiveness recognized for fair value hedge			(2)
Fixed maturities | Foreign currency options
Derivative Instruments, Gain (Loss) [Line Items]
Total gains (losses) recognized for derivatives	21	(95)	(4)
Gains (losses) on derivatives excluded from effectiveness testing	10	(18)	3
Gains (losses) on derivatives included in effectiveness testing	11	(77)	(7)
Gains (losses) recognized for hedged items	(10)	70	7
Ineffectiveness recognized for fair value hedge	$ 1	$ (7)	0
Fixed maturities | Interest rate swaptions
Derivative Instruments, Gain (Loss) [Line Items]
Total gains (losses) recognized for derivatives			(95)
Gains (losses) on derivatives excluded from effectiveness testing			19
Gains (losses) on derivatives included in effectiveness testing			(114)
Gains (losses) recognized for hedged items			99
Ineffectiveness recognized for fair value hedge			$ (15)

DERIVATIVE INSTRUMENTS - Deriva

DERIVATIVE INSTRUMENTS - Derivatives and Hedging Instruments Gain (Loss) Summary (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized foreign currency translation gains (losses) during period		$ 286	$ 283	$ 360
Derivative and other gains (losses)		(109)	(255)	(10)
Derivative and non-derivative hedging instruments gain loss recognized in other comprehensive income effective portion before tax	[1]	(34)	(42)	7
Cash flow hedges
Derivative Instruments, Gain (Loss) [Line Items]
Net Realized Investment Gains (Losses) Recognized in Income on Derivative (Ineffective Portion)		0	1	0
Gain (Loss) Recognized in Other Comprehensive Income on Derivative (Effective Portion)	[1]	1	3	0
Cash flow hedges | Foreign currency swaps
Derivative Instruments, Gain (Loss) [Line Items]
Net Realized Investment Gains (Losses) Recognized in Income on Derivative (Ineffective Portion)		0	1	0
Gain (Loss) Recognized in Other Comprehensive Income on Derivative (Effective Portion)	[1]	1	3	0
Fair value hedges
Derivative Instruments, Gain (Loss) [Line Items]
Net Realized Investment Gains (Losses) Recognized in Income on Derivative (Ineffective Portion)		(169)	(384)	(131)
Gain (Loss) Recognized in Other Comprehensive Income on Derivative (Effective Portion)	[1]	0	0	0
Fair value hedges | Foreign currency forwards
Derivative Instruments, Gain (Loss) [Line Items]
Net Realized Investment Gains (Losses) Recognized in Income on Derivative (Ineffective Portion)	[2]	(180)	(359)	(138)
Gain (Loss) Recognized in Other Comprehensive Income on Derivative (Effective Portion)	[1],[2]	0	0	0
Fair value hedges | Foreign currency options
Derivative Instruments, Gain (Loss) [Line Items]
Net Realized Investment Gains (Losses) Recognized in Income on Derivative (Ineffective Portion)	[2]	11	(25)	3
Gain (Loss) Recognized in Other Comprehensive Income on Derivative (Effective Portion)	[1],[2]	0	0	0
Fair value hedges | Interest rate swaptions
Derivative Instruments, Gain (Loss) [Line Items]
Net Realized Investment Gains (Losses) Recognized in Income on Derivative (Ineffective Portion)	[2]	0	0	4
Gain (Loss) Recognized in Other Comprehensive Income on Derivative (Effective Portion)	[1],[2]	0	0	0
Net investment hedge
Derivative Instruments, Gain (Loss) [Line Items]
Net Realized Investment Gains (Losses) Recognized in Income on Derivative (Ineffective Portion)		0	0	0
Unrealized foreign currency translation gains (losses) during period	[1]	(35)	(45)	7
Net investment hedge | Foreign currency forwards
Derivative Instruments, Gain (Loss) [Line Items]
Net Realized Investment Gains (Losses) Recognized in Income on Derivative (Ineffective Portion)		0	0	0
Unrealized foreign currency translation gains (losses) during period	[1]	(25)	(118)	4
Net investment hedge | Foreign currency options
Derivative Instruments, Gain (Loss) [Line Items]
Net Realized Investment Gains (Losses) Recognized in Income on Derivative (Ineffective Portion)		0	0	0
Unrealized foreign currency translation gains (losses) during period	[1]	5	73	0
Net investment hedge | Non-derivative hedging instruments
Derivative Instruments, Gain (Loss) [Line Items]
Net Realized Investment Gains (Losses) Recognized in Income on Derivative (Ineffective Portion)		0	0	0
Unrealized foreign currency translation gains (losses) during period	[1]	(15)	0	3
Non-qualifying strategies
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Gain (Loss) Recognized in Income, Net		60	128	121
Gain (Loss) Recognized in Other Comprehensive Income on Derivative (Effective Portion)	[1]	0	0	0
Non-qualifying strategies | Foreign currency swaps
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Gain (Loss) Recognized in Income, Net		53	117	16
Gain (Loss) Recognized in Other Comprehensive Income on Derivative (Effective Portion)	[1]	0	0	0
Non-qualifying strategies | Foreign currency forwards
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Gain (Loss) Recognized in Income, Net		8	9	100
Gain (Loss) Recognized in Other Comprehensive Income on Derivative (Effective Portion)	[1]	0	0	0
Non-qualifying strategies | Credit default swaps
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Gain (Loss) Recognized in Income, Net		(1)	2	1
Gain (Loss) Recognized in Other Comprehensive Income on Derivative (Effective Portion)	[1]	0	0	0
Non-qualifying strategies | Interest rate swaps
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Gain (Loss) Recognized in Income, Net		0	0	5
Gain (Loss) Recognized in Other Comprehensive Income on Derivative (Effective Portion)	[1]	0	0	0
Non-qualifying strategies | Futures
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Gain (Loss) Recognized in Income, Net		0	0	(1)
Gain (Loss) Recognized in Other Comprehensive Income on Derivative (Effective Portion)	[1]	$ 0	$ 0	$ 0
[1]	Cash flow hedge items are recorded as unrealized gains (losses) on derivatives and net investment hedge items are recorded in the unrealized foreign currency translation gains (losses) line in the consolidated statement of comprehensive income (loss).
[2]	Impact shown net of effect of hedged items (see Fair Value Hedges section of this Note 4 for further detail)

DERIVATIVE INSTRUMENTS - Offset

DERIVATIVE INSTRUMENTS - Offsetting of Financial Assets and Derivative Assets (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Offsetting Assets [Line Items]
Gross amount of recognized derivative assets	$ 180	$ 1,080
Gross amount of liabilities offset in balance sheet	0	0
Net amount of derivative assets presented in balance sheet	180	1,080
Financial instruments, amounts not offset	(82)	(698)
Derivative, collateral, obligation to return securities	0	0
Derivative, collateral, obligation to return cash	(98)	(382)
Derivative asset, fair value, amount offset against collateral, subject to master netting agreement	0	0
Derivative asset, not subject to master netting arrangement	151	127
Derivative asset, fair value, amount offset against collateral, not subject to master netting agreement	151	127
Derivative asset, fair value, gross asset including not subject to master netting arrangement	331	1,207
Net amount of derivative assets presented in balance sheet	331	1,207
Derivative asset, fair value, amount offset against collateral	151	127
Gross amounts of recognized financial instruments	923	1,720
Gross amounts offset in balance sheet	0	0
Net amounts of assets presented in balance sheet	923	1,720
Carrying value of assets not offset in balance sheet	(82)	(698)
Securities collateral, not offset in balance sheet	0	0
Cash collateral, not offset in balance sheet	(690)	(895)
Financial instruments, amount of assets offset against collateral	151	127
Securities lending and similar arrangements
Offsetting Assets [Line Items]
Gross amounts of recognized financial instruments	592	513
Gross amounts offset in balance sheet	0	0
Net amounts of assets presented in balance sheet	592	513
Carrying value of assets not offset in balance sheet	0	0
Securities collateral, not offset in balance sheet	0	0
Cash collateral, not offset in balance sheet	(592)	(513)
Financial instruments, amount of assets offset against collateral	$ 0	$ 0

DERIVATIVE INSTRUMENTS - Offs74

DERIVATIVE INSTRUMENTS - Offsetting of Financial Liabilities and Derivative Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Offsetting Liabilities [Line Items]
Gross amount of recognized derivative liabilities	$ (346)	$ (1,852)
Gross amount of assets offset in balance sheet	0	0
Derivative liability, fair value, amount not offset against collateral	(346)	(1,852)
Financial instruments, amounts not offset	82	698
Derivative, collateral, right to reclaim securities	245	1,130
Derivative, collateral, right to reclaim cash	10	21
Derivative liability, fair value, amount offset against collateral, subject to master netting agreement	(9)	(3)
Derivative liability, not subject to master netting arrangement	(128)	(146)
Derivative liability, fair value, amount offset against collateral, not subject to master netting agreement	(128)	(146)
Derivative liability, fair value, gross liability including not subject to master netting arrangement	(474)	(1,998)
Net amount of derivative liabilities presented in balance sheet	(474)	(1,998)
Derivative liability, fair value, amount offset against collateral	(137)	(149)
Gross Amounts of Recognized Financial Instruments, Offsetting Liabilities	(1,080)	(2,524)
Gross Amounts Offset in Statement of Financial Position, Offsetting Liabilities	0	0
Net Amounts of Financial Instruments Presented in Balance Sheet, Offsetting Liabilities	(1,080)	(2,524)
Carrying value of financial instruments, liabilities not offset in balance sheet	674	1,211
Securities Collateral, Liabilities Not Offset in Balance Sheet	245	1,130
Cash Collateral, Liabilities Not Offset in Balance Sheet	10	21
Financial instruments, amount of liabilities offset against collateral	(151)	(162)
Securities lending and similar arrangements
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Financial Instruments, Offsetting Liabilities	(606)	(526)
Gross Amounts Offset in Statement of Financial Position, Offsetting Liabilities	0	0
Net Amounts of Financial Instruments Presented in Balance Sheet, Offsetting Liabilities	(606)	(526)
Carrying value of financial instruments, liabilities not offset in balance sheet	592	513
Securities Collateral, Liabilities Not Offset in Balance Sheet	0	0
Cash Collateral, Liabilities Not Offset in Balance Sheet	0	0
Financial instruments, amount of liabilities offset against collateral	$ (14)	$ (13)

DERIVATIVE INSTRUMENTS - Fair V

DERIVATIVE INSTRUMENTS - Fair Value and Notional Amount of Derivatives with Counterparty Credit Risk (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Fair Value and Notional Amount of Derivatives with Counterparty Credit RIsk [Line Items]
Notional Amount of Derivatives	$ 25,751	$ 43,927
Asset Derivatives Fair Value	331	1,207
Liability Derivatives Fair Value	(474)	(1,998)
AA
Fair Value and Notional Amount of Derivatives with Counterparty Credit RIsk [Line Items]
Notional Amount of Derivatives	4,708	6,844
Asset Derivatives Fair Value	52	247
Liability Derivatives Fair Value	(37)	(308)
A
Fair Value and Notional Amount of Derivatives with Counterparty Credit RIsk [Line Items]
Notional Amount of Derivatives	20,604	36,019
Asset Derivatives Fair Value	271	900
Liability Derivatives Fair Value	(370)	(1,621)
BBB
Fair Value and Notional Amount of Derivatives with Counterparty Credit RIsk [Line Items]
Notional Amount of Derivatives	439	1,064
Asset Derivatives Fair Value	8	60
Liability Derivatives Fair Value	$ (67)	$ (69)

FAIR VALUE MEASUREMENTS - Fair

FAIR VALUE MEASUREMENTS - Fair Value Hierarchy Levels of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Assets:
Available-for-sale securities	$ 85,336	$ 76,702
Asset derivatives	331	1,207
Other investments	57	276
Cash and cash equivalents	3,491	4,859
Total assets	89,215	83,044
Liabilities:
Liability derivatives	474	1,998
Total liabilities	474	1,998
Foreign currency swaps
Assets:
Asset derivatives	296	490
Liabilities:
Liability derivatives	197	230
Foreign currency forwards
Assets:
Asset derivatives	22	672
Liabilities:
Liability derivatives	274	1,717
Foreign currency options
Assets:
Asset derivatives	12	43
Liabilities:
Liability derivatives	3	51
Credit default swaps
Assets:
Asset derivatives	1	2
Fixed maturities
Assets:
Available-for-sale securities	82,524	73,760
Fixed maturities | Government and agencies
Assets:
Available-for-sale securities	31,230	26,214
Fixed maturities | Municipalities
Assets:
Available-for-sale securities	1,370	1,295
Fixed maturities | Mortgage- and asset-backed securities
Assets:
Available-for-sale securities	444	1,337
Fixed maturities | Public utilities
Assets:
Available-for-sale securities	7,954	7,683
Fixed maturities | Sovereign and supranational
Assets:
Available-for-sale securities	1,909	1,469
Fixed maturities | Banks/financial institutions
Assets:
Available-for-sale securities	7,377	6,063
Fixed maturities | Other corporate
Assets:
Available-for-sale securities	32,240	29,699
Perpetual securities
Assets:
Available-for-sale securities	1,789	1,633
Perpetual securities | Banks/financial institutions
Assets:
Available-for-sale securities	1,556	1,420
Perpetual securities | Other corporate
Assets:
Available-for-sale securities	233	213
Equity securities
Assets:
Available-for-sale securities	1,023	1,309
Level 1
Assets:
Available-for-sale securities	31,110	26,687
Asset derivatives	0	0
Other investments	57	276
Cash and cash equivalents	3,491	4,859
Total assets	34,658	31,822
Liabilities:
Total liabilities	0	0
Level 1 | Foreign currency swaps
Assets:
Asset derivatives	0	0
Liabilities:
Liability derivatives	0	0
Level 1 | Foreign currency forwards
Assets:
Asset derivatives	0	0
Liabilities:
Liability derivatives	0	0
Level 1 | Foreign currency options
Assets:
Asset derivatives	0	0
Liabilities:
Liability derivatives	0	0
Level 1 | Credit default swaps
Assets:
Asset derivatives	0	0
Level 1 | Fixed maturities
Assets:
Available-for-sale securities	30,109	25,387
Level 1 | Fixed maturities | Government and agencies
Assets:
Available-for-sale securities	30,109	25,387
Level 1 | Fixed maturities | Municipalities
Assets:
Available-for-sale securities	0	0
Level 1 | Fixed maturities | Mortgage- and asset-backed securities
Assets:
Available-for-sale securities	0	0
Level 1 | Fixed maturities | Public utilities
Assets:
Available-for-sale securities	0	0
Level 1 | Fixed maturities | Sovereign and supranational
Assets:
Available-for-sale securities	0	0
Level 1 | Fixed maturities | Banks/financial institutions
Assets:
Available-for-sale securities	0	0
Level 1 | Fixed maturities | Other corporate
Assets:
Available-for-sale securities	0	0
Level 1 | Perpetual securities
Assets:
Available-for-sale securities	0	0
Level 1 | Perpetual securities | Banks/financial institutions
Assets:
Available-for-sale securities	0	0
Level 1 | Perpetual securities | Other corporate
Assets:
Available-for-sale securities	0	0
Level 1 | Equity securities
Assets:
Available-for-sale securities	1,001	1,300
Level 2
Assets:
Available-for-sale securities	53,796	49,773
Asset derivatives	180	1,080
Other investments	0	0
Cash and cash equivalents	0	0
Total assets	53,976	50,853
Liabilities:
Total liabilities	346	1,852
Level 2 | Foreign currency swaps
Assets:
Asset derivatives	146	365
Liabilities:
Liability derivatives	69	84
Level 2 | Foreign currency forwards
Assets:
Asset derivatives	22	672
Liabilities:
Liability derivatives	274	1,717
Level 2 | Foreign currency options
Assets:
Asset derivatives	12	43
Liabilities:
Liability derivatives	3	51
Level 2 | Credit default swaps
Assets:
Asset derivatives	0	0
Level 2 | Fixed maturities
Assets:
Available-for-sale securities	52,001	48,134
Level 2 | Fixed maturities | Government and agencies
Assets:
Available-for-sale securities	1,121	827
Level 2 | Fixed maturities | Municipalities
Assets:
Available-for-sale securities	1,370	1,295
Level 2 | Fixed maturities | Mortgage- and asset-backed securities
Assets:
Available-for-sale securities	269	1,139
Level 2 | Fixed maturities | Public utilities
Assets:
Available-for-sale securities	7,886	7,667
Level 2 | Fixed maturities | Sovereign and supranational
Assets:
Available-for-sale securities	1,909	1,469
Level 2 | Fixed maturities | Banks/financial institutions
Assets:
Available-for-sale securities	7,352	6,038
Level 2 | Fixed maturities | Other corporate
Assets:
Available-for-sale securities	32,094	29,699
Level 2 | Perpetual securities
Assets:
Available-for-sale securities	1,789	1,633
Level 2 | Perpetual securities | Banks/financial institutions
Assets:
Available-for-sale securities	1,556	1,420
Level 2 | Perpetual securities | Other corporate
Assets:
Available-for-sale securities	233	213
Level 2 | Equity securities
Assets:
Available-for-sale securities	6	6
Level 3
Assets:
Available-for-sale securities	430	242
Asset derivatives	151	127
Other investments	0	0
Cash and cash equivalents	0	0
Total assets	581	369
Liabilities:
Total liabilities	128	146
Level 3 | Foreign currency swaps
Assets:
Asset derivatives	150	125
Liabilities:
Liability derivatives	128	146
Level 3 | Foreign currency forwards
Assets:
Asset derivatives	0	0
Liabilities:
Liability derivatives	0	0
Level 3 | Foreign currency options
Assets:
Asset derivatives	0	0
Liabilities:
Liability derivatives	0	0
Level 3 | Credit default swaps
Assets:
Asset derivatives	1	2
Level 3 | Fixed maturities
Assets:
Available-for-sale securities	414	239
Level 3 | Fixed maturities | Government and agencies
Assets:
Available-for-sale securities	0	0
Level 3 | Fixed maturities | Municipalities
Assets:
Available-for-sale securities	0	0
Level 3 | Fixed maturities | Mortgage- and asset-backed securities
Assets:
Available-for-sale securities	175	198
Level 3 | Fixed maturities | Public utilities
Assets:
Available-for-sale securities	68	16
Level 3 | Fixed maturities | Sovereign and supranational
Assets:
Available-for-sale securities	0	0
Level 3 | Fixed maturities | Banks/financial institutions
Assets:
Available-for-sale securities	25	25
Level 3 | Fixed maturities | Other corporate
Assets:
Available-for-sale securities	146	0
Level 3 | Perpetual securities
Assets:
Available-for-sale securities	0	0
Level 3 | Perpetual securities | Banks/financial institutions
Assets:
Available-for-sale securities	0	0
Level 3 | Perpetual securities | Other corporate
Assets:
Available-for-sale securities	0	0
Level 3 | Equity securities
Assets:
Available-for-sale securities	$ 16	$ 3

FAIR VALUE MEASUREMENTS - Fai77

FAIR VALUE MEASUREMENTS - Fair Value Hierarchy Levels of Assets and Liabilities Carried at Cost or Amortized Cost (Details) - USD ($) $ in Millions		Dec. 31, 2017		Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	[1]	$ 3,402		$ 1,450
Assets:
Securities held to maturity, fixed maturities, amortized cost		31,430		33,350
Securities held to maturity, fixed maturities, fair value		38,072		40,021
Other investments, carried at amortized cost		3,017	[2]	1,174
Other investments, carried at amortized cost, fair value		3,002	[2]	1,142
Total financial instruments, assets, not carried at fair value		34,447		34,524
Assets, fair value disclosure, financial instruments, carried at cost		41,074		41,163
Liabilities:
Other policyholders' funds		6,939		6,659
Other policyholders' funds fair value disclosure		6,841		6,540
Notes payable		5,267		5,339
Notes payable, fair value disclosure		5,553		5,530
Total financial instrument liabilities not carried at fair value		12,206		11,998
Liabilities fair value disclosure financial instruments carried at cost		12,394		12,070
Fixed maturities
Assets:
Securities held to maturity, fixed maturities, fair value		38,072		40,021
Government and agencies | Fixed maturities
Assets:
Securities held to maturity, fixed maturities, amortized cost		21,331		20,702
Securities held to maturity, fixed maturities, fair value		26,491		26,040
Municipalities | Fixed maturities
Assets:
Securities held to maturity, fixed maturities, amortized cost		357		350
Securities held to maturity, fixed maturities, fair value		462		457
Mortgage- and asset-backed securities | Fixed maturities
Assets:
Securities held to maturity, fixed maturities, amortized cost		26		30
Securities held to maturity, fixed maturities, fair value		27		32
Public utilities | Fixed maturities
Assets:
Securities held to maturity, fixed maturities, amortized cost		3,300		3,201
Securities held to maturity, fixed maturities, fair value		3,698		3,536
Sovereign and supranational | Fixed maturities
Assets:
Securities held to maturity, fixed maturities, amortized cost		1,523		2,602
Securities held to maturity, fixed maturities, fair value		1,835		2,877
Banks/financial institutions | Fixed maturities
Assets:
Securities held to maturity, fixed maturities, amortized cost		2,206		3,731
Securities held to maturity, fixed maturities, fair value		2,387		3,900
Other corporate | Fixed maturities
Assets:
Securities held to maturity, fixed maturities, amortized cost		2,687		2,734
Securities held to maturity, fixed maturities, fair value		3,172		3,179
Policy loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments		210		184
Equity method investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments		118
Level 1
Assets:
Other investments, carried at amortized cost, fair value		0	[2]	0
Assets, fair value disclosure, financial instruments, carried at cost		26,491		26,040
Liabilities:
Other policyholders' funds fair value disclosure		0		0
Notes payable, fair value disclosure		0		0
Liabilities fair value disclosure financial instruments carried at cost		0		0
Level 1 | Fixed maturities
Assets:
Securities held to maturity, fixed maturities, fair value		26,491		26,040
Level 1 | Government and agencies | Fixed maturities
Assets:
Securities held to maturity, fixed maturities, fair value		26,491		26,040
Level 1 | Municipalities | Fixed maturities
Assets:
Securities held to maturity, fixed maturities, fair value		0		0
Level 1 | Mortgage- and asset-backed securities | Fixed maturities
Assets:
Securities held to maturity, fixed maturities, fair value		0		0
Level 1 | Public utilities | Fixed maturities
Assets:
Securities held to maturity, fixed maturities, fair value		0		0
Level 1 | Sovereign and supranational | Fixed maturities
Assets:
Securities held to maturity, fixed maturities, fair value		0		0
Level 1 | Banks/financial institutions | Fixed maturities
Assets:
Securities held to maturity, fixed maturities, fair value		0		0
Level 1 | Other corporate | Fixed maturities
Assets:
Securities held to maturity, fixed maturities, fair value		0		0
Level 2
Assets:
Other investments, carried at amortized cost, fair value		15	[2]	0
Assets, fair value disclosure, financial instruments, carried at cost		11,577		13,959
Liabilities:
Other policyholders' funds fair value disclosure		0		0
Notes payable, fair value disclosure		5,288		0
Liabilities fair value disclosure financial instruments carried at cost		5,288		0
Level 2 | Fixed maturities
Assets:
Securities held to maturity, fixed maturities, fair value		11,562		13,959
Level 2 | Government and agencies | Fixed maturities
Assets:
Securities held to maturity, fixed maturities, fair value		0		0
Level 2 | Municipalities | Fixed maturities
Assets:
Securities held to maturity, fixed maturities, fair value		462		457
Level 2 | Mortgage- and asset-backed securities | Fixed maturities
Assets:
Securities held to maturity, fixed maturities, fair value		8		10
Level 2 | Public utilities | Fixed maturities
Assets:
Securities held to maturity, fixed maturities, fair value		3,698		3,536
Level 2 | Sovereign and supranational | Fixed maturities
Assets:
Securities held to maturity, fixed maturities, fair value		1,835		2,877
Level 2 | Banks/financial institutions | Fixed maturities
Assets:
Securities held to maturity, fixed maturities, fair value		2,387		3,900
Level 2 | Other corporate | Fixed maturities
Assets:
Securities held to maturity, fixed maturities, fair value		3,172		3,179
Level 3
Assets:
Other investments, carried at amortized cost, fair value		2,987	[2]	1,142
Assets, fair value disclosure, financial instruments, carried at cost		3,006		1,164
Liabilities:
Other policyholders' funds fair value disclosure		6,841		6,540
Notes payable, fair value disclosure		265		5,530
Liabilities fair value disclosure financial instruments carried at cost		7,106		12,070
Level 3 | Fixed maturities
Assets:
Securities held to maturity, fixed maturities, fair value		19		22
Level 3 | Government and agencies | Fixed maturities
Assets:
Securities held to maturity, fixed maturities, fair value		0		0
Level 3 | Municipalities | Fixed maturities
Assets:
Securities held to maturity, fixed maturities, fair value		0		0
Level 3 | Mortgage- and asset-backed securities | Fixed maturities
Assets:
Securities held to maturity, fixed maturities, fair value		19		22
Level 3 | Public utilities | Fixed maturities
Assets:
Securities held to maturity, fixed maturities, fair value		0		0
Level 3 | Sovereign and supranational | Fixed maturities
Assets:
Securities held to maturity, fixed maturities, fair value		0		0
Level 3 | Banks/financial institutions | Fixed maturities
Assets:
Securities held to maturity, fixed maturities, fair value		0		0
Level 3 | Other corporate | Fixed maturities
Assets:
Securities held to maturity, fixed maturities, fair value		$ 0		$ 0
[1]	Includes $2,341 in 2017 and $819 in 2016 of loan receivables and limited partnerships from consolidated variable interest entities
[2]	Excludes policy loans of $210 and equity method investments of $118, at carrying value

FAIR VALUE MEASUREMENTS - Fai78

FAIR VALUE MEASUREMENTS - Fair Value Hierarchy Levels of Assets by Pricing Source, Available-for-sale Securities (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	$ 85,336	$ 76,702
Level 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	31,110	26,687
Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	53,796	49,773
Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	430	242
Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	82,524	73,760
Fixed maturities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	30,109	25,387
Fixed maturities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	52,001	48,134
Fixed maturities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	414	239
Perpetual securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	1,789	1,633
Perpetual securities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	0	0
Perpetual securities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	1,789	1,633
Perpetual securities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	0	0
Equity securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	1,023	1,309
Equity securities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	1,001	1,300
Equity securities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	6	6
Equity securities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	16	3
Equity securities | Third party pricing vendor valuation technique
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	1,007	1,306
Equity securities | Third party pricing vendor valuation technique | Level 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	1,001	1,300
Equity securities | Third party pricing vendor valuation technique | Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	6	6
Equity securities | Third party pricing vendor valuation technique | Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	0	0
Equity securities | Net asset value valuation technique
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	16	3
Equity securities | Net asset value valuation technique | Level 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	0	0
Equity securities | Net asset value valuation technique | Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	0	0
Equity securities | Net asset value valuation technique | Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	16	3
Government and agencies | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	31,230	26,214
Government and agencies | Fixed maturities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	30,109	25,387
Government and agencies | Fixed maturities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	1,121	827
Government and agencies | Fixed maturities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	0	0
Government and agencies | Fixed maturities | Third party pricing vendor valuation technique
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	31,230	26,214
Government and agencies | Fixed maturities | Third party pricing vendor valuation technique | Level 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	30,109	25,387
Government and agencies | Fixed maturities | Third party pricing vendor valuation technique | Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	1,121	827
Government and agencies | Fixed maturities | Third party pricing vendor valuation technique | Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	0	0
Municipalities | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	1,370	1,295
Municipalities | Fixed maturities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	0	0
Municipalities | Fixed maturities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	1,370	1,295
Municipalities | Fixed maturities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	0	0
Municipalities | Fixed maturities | Third party pricing vendor valuation technique
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	1,370	1,295
Municipalities | Fixed maturities | Third party pricing vendor valuation technique | Level 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	0	0
Municipalities | Fixed maturities | Third party pricing vendor valuation technique | Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	1,370	1,295
Municipalities | Fixed maturities | Third party pricing vendor valuation technique | Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	0	0
Mortgage- and asset-backed securities | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	444	1,337
Mortgage- and asset-backed securities | Fixed maturities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	0	0
Mortgage- and asset-backed securities | Fixed maturities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	269	1,139
Mortgage- and asset-backed securities | Fixed maturities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	175	198
Mortgage- and asset-backed securities | Fixed maturities | Third party pricing vendor valuation technique
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	269	1,139
Mortgage- and asset-backed securities | Fixed maturities | Third party pricing vendor valuation technique | Level 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	0	0
Mortgage- and asset-backed securities | Fixed maturities | Third party pricing vendor valuation technique | Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	269	1,139
Mortgage- and asset-backed securities | Fixed maturities | Third party pricing vendor valuation technique | Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	0	0
Mortgage- and asset-backed securities | Fixed maturities | Consensus pricing valuation technique
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	175	198
Mortgage- and asset-backed securities | Fixed maturities | Consensus pricing valuation technique | Level 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	0	0
Mortgage- and asset-backed securities | Fixed maturities | Consensus pricing valuation technique | Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	0	0
Mortgage- and asset-backed securities | Fixed maturities | Consensus pricing valuation technique | Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	175	198
Public utilities | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	7,954	7,683
Public utilities | Fixed maturities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	0	0
Public utilities | Fixed maturities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	7,886	7,667
Public utilities | Fixed maturities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	68	16
Public utilities | Fixed maturities | Third party pricing vendor valuation technique
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	7,886	7,667
Public utilities | Fixed maturities | Third party pricing vendor valuation technique | Level 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	0	0
Public utilities | Fixed maturities | Third party pricing vendor valuation technique | Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	7,886	7,667
Public utilities | Fixed maturities | Third party pricing vendor valuation technique | Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	0	0
Public utilities | Fixed maturities | Discounted cash flow valuation technique
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	68	16
Public utilities | Fixed maturities | Discounted cash flow valuation technique | Level 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	0	0
Public utilities | Fixed maturities | Discounted cash flow valuation technique | Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	0	0
Public utilities | Fixed maturities | Discounted cash flow valuation technique | Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	68	16
Sovereign and supranational | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	1,909	1,469
Sovereign and supranational | Fixed maturities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	0	0
Sovereign and supranational | Fixed maturities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	1,909	1,469
Sovereign and supranational | Fixed maturities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	0	0
Sovereign and supranational | Fixed maturities | Third party pricing vendor valuation technique
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	1,807	1,469
Sovereign and supranational | Fixed maturities | Third party pricing vendor valuation technique | Level 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	0	0
Sovereign and supranational | Fixed maturities | Third party pricing vendor valuation technique | Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	1,807	1,469
Sovereign and supranational | Fixed maturities | Third party pricing vendor valuation technique | Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	0	0
Sovereign and supranational | Fixed maturities | Consensus pricing valuation technique
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	102
Sovereign and supranational | Fixed maturities | Consensus pricing valuation technique | Level 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	0
Sovereign and supranational | Fixed maturities | Consensus pricing valuation technique | Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	102
Sovereign and supranational | Fixed maturities | Consensus pricing valuation technique | Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	0
Banks/financial institutions | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	7,377	6,063
Banks/financial institutions | Fixed maturities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	0	0
Banks/financial institutions | Fixed maturities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	7,352	6,038
Banks/financial institutions | Fixed maturities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	25	25
Banks/financial institutions | Fixed maturities | Third party pricing vendor valuation technique
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	7,352	6,038
Banks/financial institutions | Fixed maturities | Third party pricing vendor valuation technique | Level 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	0	0
Banks/financial institutions | Fixed maturities | Third party pricing vendor valuation technique | Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	7,352	6,038
Banks/financial institutions | Fixed maturities | Third party pricing vendor valuation technique | Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	0	0
Banks/financial institutions | Fixed maturities | Consensus pricing valuation technique
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	25	25
Banks/financial institutions | Fixed maturities | Consensus pricing valuation technique | Level 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	0	0
Banks/financial institutions | Fixed maturities | Consensus pricing valuation technique | Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	0	0
Banks/financial institutions | Fixed maturities | Consensus pricing valuation technique | Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	25	25
Banks/financial institutions | Perpetual securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	1,556	1,420
Banks/financial institutions | Perpetual securities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	0	0
Banks/financial institutions | Perpetual securities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	1,556	1,420
Banks/financial institutions | Perpetual securities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	0	0
Banks/financial institutions | Perpetual securities | Third party pricing vendor valuation technique
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	1,556	1,420
Banks/financial institutions | Perpetual securities | Third party pricing vendor valuation technique | Level 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	0	0
Banks/financial institutions | Perpetual securities | Third party pricing vendor valuation technique | Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	1,556	1,420
Banks/financial institutions | Perpetual securities | Third party pricing vendor valuation technique | Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	0	0
Other corporate | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	32,240	29,699
Other corporate | Fixed maturities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	0	0
Other corporate | Fixed maturities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	32,094	29,699
Other corporate | Fixed maturities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	146	0
Other corporate | Fixed maturities | Third party pricing vendor valuation technique
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	32,094	29,699
Other corporate | Fixed maturities | Third party pricing vendor valuation technique | Level 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	0	0
Other corporate | Fixed maturities | Third party pricing vendor valuation technique | Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	32,094	29,699
Other corporate | Fixed maturities | Third party pricing vendor valuation technique | Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	0	0
Other corporate | Fixed maturities | Discounted cash flow valuation technique
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	146
Other corporate | Fixed maturities | Discounted cash flow valuation technique | Level 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	0
Other corporate | Fixed maturities | Discounted cash flow valuation technique | Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	0
Other corporate | Fixed maturities | Discounted cash flow valuation technique | Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	146
Other corporate | Perpetual securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	233	213
Other corporate | Perpetual securities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	0	0
Other corporate | Perpetual securities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	233	213
Other corporate | Perpetual securities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	0	0
Other corporate | Perpetual securities | Third party pricing vendor valuation technique
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	233	213
Other corporate | Perpetual securities | Third party pricing vendor valuation technique | Level 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	0	0
Other corporate | Perpetual securities | Third party pricing vendor valuation technique | Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	233	213
Other corporate | Perpetual securities | Third party pricing vendor valuation technique | Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale securities	$ 0	$ 0

FAIR VALUE MEASUREMENTS - Fai79

FAIR VALUE MEASUREMENTS - Fair Value Hierarchy Levels by Pricing Source, Held-to-Maturity Securities (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	$ 38,072	$ 40,021
Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	38,072	40,021
Fixed maturities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	26,491	26,040
Fixed maturities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	11,562	13,959
Fixed maturities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	19	22
Government and agencies | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	26,491	26,040
Government and agencies | Fixed maturities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	26,491	26,040
Government and agencies | Fixed maturities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	0	0
Government and agencies | Fixed maturities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	0	0
Government and agencies | Fixed maturities | Third party pricing vendor valuation technique
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	26,491	26,040
Government and agencies | Fixed maturities | Third party pricing vendor valuation technique | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	26,491	26,040
Government and agencies | Fixed maturities | Third party pricing vendor valuation technique | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	0	0
Government and agencies | Fixed maturities | Third party pricing vendor valuation technique | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	0	0
Municipalities | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	462	457
Municipalities | Fixed maturities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	0	0
Municipalities | Fixed maturities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	462	457
Municipalities | Fixed maturities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	0	0
Municipalities | Fixed maturities | Third party pricing vendor valuation technique
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	462	457
Municipalities | Fixed maturities | Third party pricing vendor valuation technique | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	0	0
Municipalities | Fixed maturities | Third party pricing vendor valuation technique | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	462	457
Municipalities | Fixed maturities | Third party pricing vendor valuation technique | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	0	0
Mortgage- and asset-backed securities | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	27	32
Mortgage- and asset-backed securities | Fixed maturities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	0	0
Mortgage- and asset-backed securities | Fixed maturities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	8	10
Mortgage- and asset-backed securities | Fixed maturities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	19	22
Mortgage- and asset-backed securities | Fixed maturities | Third party pricing vendor valuation technique
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	8	10
Mortgage- and asset-backed securities | Fixed maturities | Third party pricing vendor valuation technique | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	0	0
Mortgage- and asset-backed securities | Fixed maturities | Third party pricing vendor valuation technique | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	8	10
Mortgage- and asset-backed securities | Fixed maturities | Third party pricing vendor valuation technique | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	0	0
Mortgage- and asset-backed securities | Fixed maturities | Consensus pricing valuation technique
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	19	22
Mortgage- and asset-backed securities | Fixed maturities | Consensus pricing valuation technique | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	0	0
Mortgage- and asset-backed securities | Fixed maturities | Consensus pricing valuation technique | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	0	0
Mortgage- and asset-backed securities | Fixed maturities | Consensus pricing valuation technique | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	19	22
Public utilities | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	3,698	3,536
Public utilities | Fixed maturities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	0	0
Public utilities | Fixed maturities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	3,698	3,536
Public utilities | Fixed maturities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	0	0
Public utilities | Fixed maturities | Third party pricing vendor valuation technique
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	3,698	3,536
Public utilities | Fixed maturities | Third party pricing vendor valuation technique | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	0	0
Public utilities | Fixed maturities | Third party pricing vendor valuation technique | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	3,698	3,536
Public utilities | Fixed maturities | Third party pricing vendor valuation technique | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	0	0
Sovereign and supranational | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	1,835	2,877
Sovereign and supranational | Fixed maturities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	0	0
Sovereign and supranational | Fixed maturities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	1,835	2,877
Sovereign and supranational | Fixed maturities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	0	0
Sovereign and supranational | Fixed maturities | Third party pricing vendor valuation technique
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	1,835	2,877
Sovereign and supranational | Fixed maturities | Third party pricing vendor valuation technique | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	0	0
Sovereign and supranational | Fixed maturities | Third party pricing vendor valuation technique | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	1,835	2,877
Sovereign and supranational | Fixed maturities | Third party pricing vendor valuation technique | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	0	0
Banks/financial institutions | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	2,387	3,900
Banks/financial institutions | Fixed maturities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	0	0
Banks/financial institutions | Fixed maturities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	2,387	3,900
Banks/financial institutions | Fixed maturities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	0	0
Banks/financial institutions | Fixed maturities | Third party pricing vendor valuation technique
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	2,387	3,900
Banks/financial institutions | Fixed maturities | Third party pricing vendor valuation technique | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	0	0
Banks/financial institutions | Fixed maturities | Third party pricing vendor valuation technique | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	2,387	3,900
Banks/financial institutions | Fixed maturities | Third party pricing vendor valuation technique | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	0	0
Other corporate | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	3,172	3,179
Other corporate | Fixed maturities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	0	0
Other corporate | Fixed maturities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	3,172	3,179
Other corporate | Fixed maturities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	0	0
Other corporate | Fixed maturities | Third party pricing vendor valuation technique
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	3,172	3,179
Other corporate | Fixed maturities | Third party pricing vendor valuation technique | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	0	0
Other corporate | Fixed maturities | Third party pricing vendor valuation technique | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	3,172	3,179
Other corporate | Fixed maturities | Third party pricing vendor valuation technique | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, fixed maturities, fair value	$ 0	$ 0

FAIR VALUE MEASUREMENTS - Chang

FAIR VALUE MEASUREMENTS - Changes in Available-For-Sale Investments and Derivatives Classified as Level 3 (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017		Dec. 31, 2016
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period		$ 223		$ 58
Realized gains or losses included in earnings		42		195
Unrealized gains or losses included in other comprehensive income (loss)		5		15
Purchases		214		16
Issuances		0		0
Sales		(3)		0
Settlements		(26)		(61)
Transfers into Level 3		24		0
Transfers out of Level 3		(26)		0
Balance, end of period		453		223
Change in unrealized gain (losses) still held		42		195
Foreign currency swaps
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance, beginning of period	[1]	(21)		(192)
Realized gains or losses included in earnings	[1]	43		194
Unrealized gains or losses included in other comprehensive income (loss)	[1]	0		(22)
Purchases	[1]	0		0
Issuances	[1]	0		0
Sales	[1]	0		0
Settlements	[1]	0		(1)
Transfers into Level 3	[1]	0		0
Transfers out of Level 3	[1]	0		0
Balance, end of period	[1]	22		(21)
Change in unrealized gain (losses) still held	[1]	43		194
Credit default swaps
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance, beginning of period	[1]	2		1
Realized gains or losses included in earnings	[1]	(1)		1
Unrealized gains or losses included in other comprehensive income (loss)	[1]	0		0
Purchases	[1]	0		0
Issuances	[1]	0		0
Sales	[1]	0		0
Settlements	[1]	0		0
Transfers into Level 3	[1]	0		0
Transfers out of Level 3	[1]	0		0
Balance, end of period	[1]	1		2
Change in unrealized gain (losses) still held	[1]	(1)		1
Fixed maturities | Mortgage- and asset-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period		198		220
Realized gains or losses included in earnings		0		0
Unrealized gains or losses included in other comprehensive income (loss)		3		38
Purchases		0		0
Issuances		0		0
Sales		0		0
Settlements		(26)		(60)
Transfers into Level 3		0		0
Transfers out of Level 3		0		0
Balance, end of period		175		198
Change in unrealized gain (losses) still held		0		0
Fixed maturities | Public utilities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period		16		0
Realized gains or losses included in earnings		0		0
Unrealized gains or losses included in other comprehensive income (loss)		0		0
Purchases		76		16
Issuances		0		0
Sales		0		0
Settlements		0		0
Transfers into Level 3		0		0
Transfers out of Level 3		(24)	[2]	0
Balance, end of period		68		16
Change in unrealized gain (losses) still held		0		0
Fixed maturities | Banks/financial institutions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period		25		26
Realized gains or losses included in earnings		0		0
Unrealized gains or losses included in other comprehensive income (loss)		0		(1)
Purchases		0		0
Issuances		0		0
Sales		0		0
Settlements		0		0
Transfers into Level 3		0		0
Transfers out of Level 3		0		0
Balance, end of period		25		25
Change in unrealized gain (losses) still held		0		0
Fixed maturities | Other corporate
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period		0		0
Realized gains or losses included in earnings		0		0
Unrealized gains or losses included in other comprehensive income (loss)		2		0
Purchases		122		0
Issuances		0		0
Sales		(2)		0
Settlements		0		0
Transfers into Level 3		24	[2]	0
Transfers out of Level 3		0		0
Balance, end of period		146		0
Change in unrealized gain (losses) still held		0		0
Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period		3		3
Realized gains or losses included in earnings		0		0
Unrealized gains or losses included in other comprehensive income (loss)		0		0
Purchases		16		0
Issuances		0		0
Sales		(1)		0
Settlements		0		0
Transfers into Level 3		0		0
Transfers out of Level 3		(2)	[3]	0
Balance, end of period		16		3
Change in unrealized gain (losses) still held		$ 0		$ 0
[1]	Derivative assets and liabilities are presented net
[2]	Transfer due to sector classification change
[3]	Transfer due to change in accounting method

FAIR VALUE MEASUREMENTS - Addit

FAIR VALUE MEASUREMENTS - Additional Information (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Fair Value, Assets, Level 1 to Level 2 Transfers, Amount	$ 0	$ 0
Fair Value, Assets, Level 2 to Level 1 Transfers, Amount	$ 0	$ 0

FAIR VALUE MEASUREMENTS - Fai82

FAIR VALUE MEASUREMENTS - Fair Value Inputs Assets Quantitative Information (Details) - USD ($) $ / shares in Units, $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		$ 85,336	$ 76,702
Asset derivatives		331	1,207
Assets, fair value		89,215	$ 83,044
Length of Volatility of Japanese Yen to US Dollar Exchange Rate			10 years
Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		430	$ 242
Asset derivatives		151	127
Assets, fair value		581	369
Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		82,524	73,760
Fixed maturities | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		414	239
Equity securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		1,023	1,309
Equity securities | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		16	3
Equity securities | Net asset value valuation technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		16	3
Equity securities | Net asset value valuation technique | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		16	$ 3
Equity securities | Assets | Lower Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Offered Quotes			$ 1
Equity securities | Assets | Upper Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Offered Quotes			701
Equity securities | Assets | Weighted Average | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Offered Quotes			$ 8
Mortgage- and asset-backed securities | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		444	$ 1,337
Mortgage- and asset-backed securities | Fixed maturities | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		175	198
Mortgage- and asset-backed securities | Fixed maturities | Consensus pricing valuation technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		175	198
Mortgage- and asset-backed securities | Fixed maturities | Consensus pricing valuation technique | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		175	198
Public utilities | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		7,954	7,683
Public utilities | Fixed maturities | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		68	16
Public utilities | Fixed maturities | Discounted cash flow valuation technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		68	16
Public utilities | Fixed maturities | Discounted cash flow valuation technique | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		68	16
Banks/financial institutions | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		7,377	6,063
Banks/financial institutions | Fixed maturities | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		25	25
Banks/financial institutions | Fixed maturities | Consensus pricing valuation technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		25	25
Banks/financial institutions | Fixed maturities | Consensus pricing valuation technique | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		25	25
Other corporate | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		32,240	29,699
Other corporate | Fixed maturities | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		146	0
Other corporate | Fixed maturities | Discounted cash flow valuation technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		146
Other corporate | Fixed maturities | Discounted cash flow valuation technique | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		146
Foreign currency swaps
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Asset derivatives		296	490
Foreign currency swaps | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Asset derivatives		150	125
Credit default swaps
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Asset derivatives		1	2
Credit default swaps | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Asset derivatives		1	2
Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY), CDS Spreads and Foreign Exchange Rates | Foreign currency swaps | Discounted cash flow valuation technique | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Asset derivatives			$ 16
Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY), CDS Spreads and Foreign Exchange Rates | Foreign currency swaps | Assets | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Foreign Exchange Rates	[1]		21.47%
Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY), CDS Spreads and Foreign Exchange Rates | Foreign currency swaps | Assets | Lower Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Entity Credit Risk			0.17%
Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY), CDS Spreads and Foreign Exchange Rates | Foreign currency swaps | Assets | Upper Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Entity Credit Risk			1.72%
Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY), and CDS Spreads | Foreign currency swaps | Discounted cash flow valuation technique | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Asset derivatives		$ 80	$ 29
Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY), and CDS Spreads | Foreign currency swaps | Assets | Lower Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Entity Credit Risk		0.09%	0.16%
Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY), and CDS Spreads | Foreign currency swaps | Assets | Upper Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Entity Credit Risk		0.90%	0.88%
Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY) and Foreign Exchange Rates | Foreign currency swaps | Discounted cash flow valuation technique | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Asset derivatives			$ 80
Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY) and Foreign Exchange Rates | Foreign currency swaps | Assets | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Foreign Exchange Rates	[1]		21.47%
Fair Value, Unobservable Input, Interest Rates (USD) and Interest Rates (JPY) | Foreign currency swaps | Discounted cash flow valuation technique | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Asset derivatives		$ 70
Fair value, Unobservable Input, Base Correlation, CDS Spreads, Recovery Rate | Credit default swaps | Discounted cash flow valuation technique | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Asset derivatives		$ 1	$ 2
Fair value, Unobservable Input, Base Correlation, CDS Spreads, Recovery Rate | Credit default swaps | Assets | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Entity Credit Risk		0.25%	0.54%
Fair Value Inputs, Recovery Rate		37.24%	36.69%
Fair value, Unobservable Input, Base Correlation, CDS Spreads, Recovery Rate | Credit default swaps | Assets | Lower Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Base Correlation	[2]	46.33%	52.18%
Fair value, Unobservable Input, Base Correlation, CDS Spreads, Recovery Rate | Credit default swaps | Assets | Upper Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Base Correlation	[2]	49.65%	56.07%
Yen-denominated | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		$ 43,896	$ 37,149
Yen-denominated | Equity securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		695	705
Yen-denominated | Mortgage- and asset-backed securities | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		271	1,121
Yen-denominated | Public utilities | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		1,981	1,848
Yen-denominated | Banks/financial institutions | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		4,019	3,002
Yen-denominated | Other corporate | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		$ 4,654	$ 3,812
Yen-denominated | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY), CDS Spreads and Foreign Exchange Rates | Foreign currency swaps | Assets | Lower Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[3]		0.22%
Yen-denominated | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY), CDS Spreads and Foreign Exchange Rates | Foreign currency swaps | Assets | Upper Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[3]		0.80%
Yen-denominated | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY), and CDS Spreads | Foreign currency swaps | Assets | Lower Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[3]	0.26%	0.22%
Yen-denominated | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY), and CDS Spreads | Foreign currency swaps | Assets | Upper Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[3]	0.85%	0.80%
Yen-denominated | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY) and Foreign Exchange Rates | Foreign currency swaps | Assets | Lower Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[3]		0.22%
Yen-denominated | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY) and Foreign Exchange Rates | Foreign currency swaps | Assets | Upper Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[3]		0.80%
Yen-denominated | Fair Value, Unobservable Input, Interest Rates (USD) and Interest Rates (JPY) | Foreign currency swaps | Assets | Lower Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[3]	0.26%
Yen-denominated | Fair Value, Unobservable Input, Interest Rates (USD) and Interest Rates (JPY) | Foreign currency swaps | Assets | Upper Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[3]	0.85%
Dollar-denominated | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		$ 38,628	$ 36,611
Dollar-denominated | Equity securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		328	604
Dollar-denominated | Mortgage- and asset-backed securities | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		173	216
Dollar-denominated | Public utilities | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		5,973	5,835
Dollar-denominated | Banks/financial institutions | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		3,358	3,061
Dollar-denominated | Other corporate | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities		$ 27,586	$ 25,887
Dollar-denominated | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY), CDS Spreads and Foreign Exchange Rates | Foreign currency swaps | Assets | Lower Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[4]		2.34%
Dollar-denominated | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY), CDS Spreads and Foreign Exchange Rates | Foreign currency swaps | Assets | Upper Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[4]		2.59%
Dollar-denominated | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY), and CDS Spreads | Foreign currency swaps | Assets | Lower Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[4]	2.40%	2.34%
Dollar-denominated | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY), and CDS Spreads | Foreign currency swaps | Assets | Upper Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[4]	2.54%	2.59%
Dollar-denominated | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY) and Foreign Exchange Rates | Foreign currency swaps | Assets | Lower Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[4]		2.34%
Dollar-denominated | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY) and Foreign Exchange Rates | Foreign currency swaps | Assets | Upper Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[4]		2.59%
Dollar-denominated | Fair Value, Unobservable Input, Interest Rates (USD) and Interest Rates (JPY) | Foreign currency swaps | Assets | Lower Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[4]	2.40%
Dollar-denominated | Fair Value, Unobservable Input, Interest Rates (USD) and Interest Rates (JPY) | Foreign currency swaps | Assets | Upper Limit | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[4]	2.54%
[1]	Based on 10 year volatility of JPY/USD exchange rate
[2]	Range of base correlation for the Company's bespoke tranche for attachment and detachment points corresponding to market indices
[3]	Inputs derived from Japan long-term rates to accommodate long maturity nature of the Company's swaps
[4]	Inputs derived from U.S. long-term rates to accommodate long maturity nature of the Company's swaps

FAIR VALUE MEASUREMENTS - Fai83

FAIR VALUE MEASUREMENTS - Fair Value Inputs Liabilities Quantitative Information (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Liability derivatives		$ 474	$ 1,998
Liabilities, fair value disclosure		474	$ 1,998
Length of Volatility of Japanese Yen to US Dollar Exchange Rate			10 years
Level 3
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Liabilities, fair value disclosure		128	$ 146
Foreign currency swaps
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Liability derivatives		197	230
Foreign currency swaps | Level 3
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Liability derivatives		128	146
Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY), CDS Spreads and Foreign Exchange Rates | Foreign currency swaps | Discounted cash flow valuation technique | Level 3
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Liability derivatives			$ 113
Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY), CDS Spreads and Foreign Exchange Rates | Foreign currency swaps | Liability | Level 3
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Fair Value Inputs, Foreign Exchange Rates	[1]		21.47%
Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY), CDS Spreads and Foreign Exchange Rates | Foreign currency swaps | Liability | Lower Limit | Level 3
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Fair Value Inputs, Entity Credit Risk			0.17%
Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY), CDS Spreads and Foreign Exchange Rates | Foreign currency swaps | Liability | Upper Limit | Level 3
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Fair Value Inputs, Entity Credit Risk			1.72%
Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY), and CDS Spreads | Foreign currency swaps | Discounted cash flow valuation technique | Level 3
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Liability derivatives		$ 120	$ 23
Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY), and CDS Spreads | Foreign currency swaps | Liability | Lower Limit | Level 3
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Fair Value Inputs, Entity Credit Risk		0.13%	0.24%
Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY), and CDS Spreads | Foreign currency swaps | Liability | Upper Limit | Level 3
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Fair Value Inputs, Entity Credit Risk		1.57%	2.16%
Fair Value, Unobservable Input, Interest Rates (USD) and Interest Rates (JPY) | Foreign currency swaps | Discounted cash flow valuation technique | Level 3
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Liability derivatives		$ 8
Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY) and Foreign Exchange Rates | Foreign currency swaps | Discounted cash flow valuation technique | Level 3
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Liability derivatives			$ 10
Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY) and Foreign Exchange Rates | Foreign currency swaps | Liability | Level 3
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Fair Value Inputs, Foreign Exchange Rates	[1]		21.47%
Yen-denominated | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY), CDS Spreads and Foreign Exchange Rates | Foreign currency swaps | Liability | Lower Limit | Level 3
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[2]		0.22%
Yen-denominated | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY), CDS Spreads and Foreign Exchange Rates | Foreign currency swaps | Liability | Upper Limit | Level 3
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[2]		0.80%
Yen-denominated | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY), and CDS Spreads | Foreign currency swaps | Liability | Lower Limit | Level 3
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[2]	0.26%	0.22%
Yen-denominated | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY), and CDS Spreads | Foreign currency swaps | Liability | Upper Limit | Level 3
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[2]	0.85%	0.80%
Yen-denominated | Fair Value, Unobservable Input, Interest Rates (USD) and Interest Rates (JPY) | Foreign currency swaps | Liability | Lower Limit | Level 3
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[2]	0.26%
Yen-denominated | Fair Value, Unobservable Input, Interest Rates (USD) and Interest Rates (JPY) | Foreign currency swaps | Liability | Upper Limit | Level 3
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[2]	0.85%
Yen-denominated | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY) and Foreign Exchange Rates | Foreign currency swaps | Liability | Lower Limit | Level 3
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[2]		0.22%
Yen-denominated | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY) and Foreign Exchange Rates | Foreign currency swaps | Liability | Upper Limit | Level 3
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[2]		0.80%
Dollar-denominated | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY), CDS Spreads and Foreign Exchange Rates | Foreign currency swaps | Liability | Lower Limit | Level 3
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[3]		2.34%
Dollar-denominated | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY), CDS Spreads and Foreign Exchange Rates | Foreign currency swaps | Liability | Upper Limit | Level 3
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[3]		2.59%
Dollar-denominated | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY), and CDS Spreads | Foreign currency swaps | Liability | Lower Limit | Level 3
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[3]	2.40%	2.34%
Dollar-denominated | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY), and CDS Spreads | Foreign currency swaps | Liability | Upper Limit | Level 3
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[3]	2.54%	2.59%
Dollar-denominated | Fair Value, Unobservable Input, Interest Rates (USD) and Interest Rates (JPY) | Foreign currency swaps | Liability | Lower Limit | Level 3
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[3]	2.40%
Dollar-denominated | Fair Value, Unobservable Input, Interest Rates (USD) and Interest Rates (JPY) | Foreign currency swaps | Liability | Upper Limit | Level 3
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[3]	2.54%
Dollar-denominated | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY) and Foreign Exchange Rates | Foreign currency swaps | Liability | Lower Limit | Level 3
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[3]		2.34%
Dollar-denominated | Fair Value, Unobservable Input, Interest Rates (USD), Interest Rates (JPY) and Foreign Exchange Rates | Foreign currency swaps | Liability | Upper Limit | Level 3
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	[3]		2.59%
[1]	Based on 10 year volatility of JPY/USD exchange rate
[2]	Inputs derived from Japan long-term rates to accommodate long maturity nature of the Company's swaps
[3]	Inputs derived from U.S. long-term rates to accommodate long maturity nature of the Company's swaps

DEFERRED POLICY ACQUISITION C84

DEFERRED POLICY ACQUISITION COSTS AND INSURANCE EXPENSES - Additional Information (Detail) - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred Policy Acquisition Costs Disclosures [Abstract]
Capitalization of deferred policy acquisition costs	$ 1.5	$ 1.4	$ 1.3
Commissions deferred as a percentage of total acquisition costs	72.00%	74.00%	74.00%
Personnel, compensation and benefit expenses as a percentage of insurance expenses	56.00%	53.00%	52.00%

DEFERRED POLICY ACQUISITION C85

DEFERRED POLICY ACQUISITION COSTS AND INSURANCE EXPENSES - Rollforward of Deferred Policy Acquisition Costs by Segment (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred policy acquisition costs:
Balance, beginning of year	$ 8,993
Capitalization	1,500	$ 1,400	$ 1,300
Amortization	(1,132)	(1,141)	(1,066)
Balance, end of year	9,505	8,993
Aflac Japan
Deferred policy acquisition costs:
Balance, beginning of year	5,765	5,370
Capitalization	839	864
Amortization	(630)	(644)	(578)
Foreign currency translation and other	176	175
Balance, end of year	6,150	5,765	5,370
Aflac U.S.
Deferred policy acquisition costs:
Balance, beginning of year	3,228	3,141
Capitalization	629	583
Amortization	(502)	(497)	(488)
Foreign currency translation and other	0	1
Balance, end of year	$ 3,355	$ 3,228	$ 3,141

DEFERRED POLICY ACQUISITION C86

DEFERRED POLICY ACQUISITION COSTS AND INSURANCE EXPENSES - Advertising Expense (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Advertising Costs [Line Items]
Advertising expense	$ 210	$ 224	$ 211
Aflac Japan
Advertising Costs [Line Items]
Advertising expense	100	100	82
Aflac U.S.
Advertising Costs [Line Items]
Advertising expense	$ 110	$ 124	$ 129

DEFERRED POLICY ACQUISITION C87

DEFERRED POLICY ACQUISITION COSTS AND INSURANCE EXPENSES - Depreciation and Other Amortization Expense (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred Policy Acquisition Costs Disclosures [Abstract]
Depreciation expense	$ 50	$ 48	$ 44
Other amortization expense	3	6	6
Total depreciation and other amortization expense	$ 53	$ 54	$ 50

DEFERRED POLICY ACQUISITION C88

DEFERRED POLICY ACQUISITION COSTS AND INSURANCE EXPENSES - Lease and Rental Expense (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Lease and Rental Expense [Line Items]
Lease and rental expense	$ 75	$ 75	$ 65
Aflac Japan
Lease and Rental Expense [Line Items]
Lease and rental expense	52	53	46
Aflac U.S.
Lease and Rental Expense [Line Items]
Lease and rental expense	21	21	18
All other
Lease and Rental Expense [Line Items]
Lease and rental expense	$ 2	$ 1	$ 1

POLICY LIABILITIES - Additional

POLICY LIABILITIES - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Liability for Future Policy Benefit, by Product Segment [Line Items]
Percentage of future policy benefits out of policy liabilities	83.00%
Percentage of unpaid policy claims out of policy liabilities	4.00%
Percentage of unearned premiums out of policy liabilities	6.00%
Percentage of other poliyholders' funds out of policy liabilities	7.00%
Percentage of advanced premiums to unearned premiums	73.00%	76.00%
Percentage of annuities to other policyholders' fund	98.00%	98.00%
Aflac Japan
Liability for Future Policy Benefit, by Product Segment [Line Items]
Weighted-average interest rates reflected in the consolidated statements of earnings for future policy benefits	3.40%	3.50%	3.60%
Aflac U.S.
Liability for Future Policy Benefit, by Product Segment [Line Items]
Weighted-average interest rates reflected in the consolidated statements of earnings for future policy benefits	5.40%	5.50%	5.60%
Health insurance
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior year claims and claims adjustment expense	$ 518	$ 465	$ 353
Health insurance | Aflac Japan
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior year claims and claims adjustment expense	$ 383
Percentage of total prior year claims and claims adjustment expense	74.00%
Liability for unpaid claims and claims adjustment expense, foreign currency translation gain (loss)	$ 18
Prior year claims and claims adjustment expense excluding effect of foreign currency	$ 400
Percentage of total prior year claims and claims adjustment expense excluding effect of foreign currency	77.00%

POLICY LIABILITIES - Liability

POLICY LIABILITIES - Liability for Future Policy Benefits (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability amounts		$ 81,857	$ 76,106
Aflac Japan
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		3.40%	3.50%	3.60%
Aflac U.S.
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		5.40%	5.50%	5.60%
Intercompany eliminations | 2015
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		2.00%
Interest Rates In 20 Years		2.00%
Liability amounts	[1]	$ (609)	$ (630)
Health insurance | Aflac Japan | 1992 - 2017
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability amounts		$ 10,167	8,912
Health insurance | Aflac Japan | 1992 - 2017 | Lower Limit
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		1.00%
Interest Rates In 20 Years		1.00%
Health insurance | Aflac Japan | 1992 - 2017 | Upper Limit
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		2.50%
Interest Rates In 20 Years		2.50%
Health insurance | Aflac Japan | 1974 - 2013
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability amounts		$ 1,133	1,118
Health insurance | Aflac Japan | 1974 - 2013 | Lower Limit
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		2.70%
Interest Rates In 20 Years		2.25%
Health insurance | Aflac Japan | 1974 - 2013 | Upper Limit
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		2.75%
Interest Rates In 20 Years		2.75%
Health insurance | Aflac Japan | 1998 - 2017
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		3.00%
Interest Rates In 20 Years		3.00%
Liability amounts		$ 12,386	11,687
Health insurance | Aflac Japan | 1997 - 1999
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		3.50%
Interest Rates In 20 Years		3.50%
Liability amounts		$ 2,454	2,485
Health insurance | Aflac Japan | 1994 - 1996
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability amounts		$ 3,046	3,069
Health insurance | Aflac Japan | 1994 - 1996 | Lower Limit
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		4.00%
Interest Rates In 20 Years		4.00%
Health insurance | Aflac Japan | 1994 - 1996 | Upper Limit
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		4.50%
Interest Rates In 20 Years		4.50%
Health insurance | Aflac Japan | 1987 - 1994
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		5.50%
Interest Rates In 20 Years		5.50%
Liability amounts		$ 14,829	14,372
Health insurance | Aflac Japan | 1985 - 1991
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability amounts		$ 1,816	1,871
Health insurance | Aflac Japan | 1985 - 1991 | Lower Limit
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		5.25%
Interest Rates In 20 Years		5.25%
Health insurance | Aflac Japan | 1985 - 1991 | Upper Limit
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		6.75%
Interest Rates In 20 Years		5.50%
Health insurance | Aflac Japan | 1978 - 1984
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		6.50%
Interest Rates In 20 Years		5.50%
Liability amounts		$ 2,037	2,134
Health insurance | Aflac U.S. | 2013 - 2017
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability amounts		$ 82	75
Health insurance | Aflac U.S. | 2013 - 2017 | Lower Limit
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		3.00%
Interest Rates In 20 Years		3.00%
Health insurance | Aflac U.S. | 2012 - 2017
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		3.75%
Interest Rates In 20 Years		3.75%
Liability amounts		$ 1,366	1,062
Health insurance | Aflac U.S. | 2011
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		4.75%
Interest Rates In 20 Years		4.75%
Liability amounts		$ 343	319
Health insurance | Aflac U.S. | 2005 - 2010
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		5.50%
Interest Rates In 20 Years		5.50%
Liability amounts		$ 2,944	3,004
Health insurance | Aflac U.S. | 1988 - 2004
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		8.00%
Interest Rates In 20 Years		6.00%
Liability amounts		$ 656	669
Health insurance | Aflac U.S. | 1986 - 2004
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		6.00%
Interest Rates In 20 Years		6.00%
Liability amounts		$ 1,296	1,265
Health insurance | Aflac U.S. | 1981 - 1986
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability amounts		$ 159	166
Health insurance | Aflac U.S. | 1981 - 1986 | Lower Limit
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		6.50%
Interest Rates In 20 Years		5.50%
Health insurance | Aflac U.S. | 1981 - 1986 | Upper Limit
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		7.00%
Interest Rates In 20 Years		6.50%
Health insurance | Aflac U.S. | 1998 - 2004
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		7.00%
Interest Rates In 20 Years		7.00%
Liability amounts		$ 1,310	1,295
Health insurance | Aflac U.S. | Other years
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability amounts		18	19
Life insurance | Aflac Japan | 2001 - 2017
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability amounts		$ 8,850	7,255
Life insurance | Aflac Japan | 2001 - 2017 | Lower Limit
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		1.00%
Interest Rates In 20 Years		1.00%
Life insurance | Aflac Japan | 2001 - 2017 | Upper Limit
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		1.85%
Interest Rates In 20 Years		1.85%
Life insurance | Aflac Japan | 2011 - 2017
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		2.00%
Interest Rates In 20 Years		2.00%
Liability amounts		$ 4,763	4,151
Life insurance | Aflac Japan | 2009 - 2011
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		2.25%
Interest Rates In 20 Years		2.25%
Liability amounts		$ 3,393	2,861
Life insurance | Aflac Japan | 1992 - 2006
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		2.19%
Interest Rates In 20 Years		1.55%
Liability amounts		$ 5	5
Life insurance | Aflac Japan | 2005 - 2011
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		2.50%
Interest Rates In 20 Years		2.50%
Liability amounts		$ 1,642	1,488
Life insurance | Aflac Japan | 1985 - 2006
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		2.70%
Interest Rates In 20 Years		2.25%
Liability amounts		$ 2,048	2,007
Life insurance | Aflac Japan | 2007 - 2011
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		2.75%
Interest Rates In 20 Years		2.75%
Liability amounts		$ 1,319	1,220
Life insurance | Aflac Japan | 1999 - 2011
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		3.00%
Interest Rates In 20 Years		3.00%
Liability amounts		$ 2,189	2,102
Life insurance | Aflac Japan | 1996 - 2009
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		3.50%
Interest Rates In 20 Years		3.50%
Liability amounts		$ 675	657
Life insurance | Aflac Japan | 1994 - 1996
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability amounts		$ 908	897
Life insurance | Aflac Japan | 1994 - 1996 | Lower Limit
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		4.00%
Interest Rates In 20 Years		4.00%
Life insurance | Aflac Japan | 1994 - 1996 | Upper Limit
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		4.50%
Interest Rates In 20 Years		4.50%
Life insurance | Aflac U.S. | 1956 - 2017
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability amounts		$ 632	$ 571
Life insurance | Aflac U.S. | 1956 - 2017 | Lower Limit
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		3.50%
Interest Rates In 20 Years		3.50%
Life insurance | Aflac U.S. | 1956 - 2017 | Upper Limit
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest Rates Year of Issue		6.00%
Interest Rates In 20 Years		6.00%
[1]	Elimination entry necessary due to recapture of a portion of policy liabilities ceded externally, as a result of the reinsurance retrocession transaction as described in Note 8 of the Notes to the Consolidated Financial Statements

POLICY LIABILITIES - Changes in

POLICY LIABILITIES - Changes in Liability for Unpaid Policy Claims (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Liability for Unpaid Claims and Claims Expenses
Unpaid supplemental health claims, beginning of year	$ 4,045	$ 3,802
Net balance, beginning of year	4,045
Less claims paid during the year on claims incurred during:
Net balance, end of year	4,392	4,045
Total liability for unpaid policy claims	4,392	4,045	$ 3,802
Health insurance
Liability for Unpaid Claims and Claims Expenses
Unpaid supplemental health claims, beginning of year	3,707	3,548	3,412
Less reinsurance recoverables	27	26	7
Net balance, beginning of year	3,680	3,522	3,405
Add claims incurred during the year related to:
Current year	6,979	7,037	6,416
Prior years	(518)	(465)	(353)
Total incurred	6,461	6,572	6,063
Less claims paid during the year on claims incurred during:
Current year	4,530	4,613	4,227
Prior years	1,822	1,865	1,718
Total paid	6,352	6,478	5,945
Effect of foreign exchange rate changes on unpaid claims	65	64	(1)
Net balance, end of year	3,854	3,680	3,522
Add reinsurance recoverables	30	27	26
Total liability for unpaid policy claims	3,884	3,707	3,548
Life insurance
Liability for Unpaid Claims and Claims Expenses
Unpaid supplemental health claims, beginning of year	338	254
Less claims paid during the year on claims incurred during:
Total liability for unpaid policy claims	$ 508	$ 338	$ 254

REINSURANCE Additional Informat

REINSURANCE Additional Information (Detail) $ in Millions, ¥ in Billions	12 Months Ended
	Dec. 31, 2017USD ($)	Dec. 31, 2017JPY (¥)	Dec. 31, 2016USD ($)
Effects of Reinsurance [Line Items]
Percent change in spot yen/dollar exchange rate	3.00%
Percent change in ceded reserves	2.00%
Aflac Japan
Effects of Reinsurance [Line Items]
Committed reinsurance facility | ¥		¥ 110
Aflac Japan | Closed Block- Tranche Three
Effects of Reinsurance [Line Items]
Coinsurance reinsurance ceded percentage	30.00%
Reinsurance assumed percentage	27.00%
Aflac Japan | Closed Medical Block - Tranche Two
Effects of Reinsurance [Line Items]
Coinsurance reinsurance ceded percentage	16.70%
Aflac Japan | Closed Medical Block - Tranche One
Effects of Reinsurance [Line Items]
Coinsurance reinsurance ceded percentage	33.30%
Aflac Japan | Closed block
Effects of Reinsurance [Line Items]
Reinsurance assumed percentage	8.35%
Reinsurance deferred profit liability	$ 954
Reinsurance recoverable	908		$ 860
Letter of credit | Closed Block- Tranche Three
Effects of Reinsurance [Line Items]
Collateral posted for reinsurance	$ 90

REINSURANCE Effect of Reinsuran

REINSURANCE Effect of Reinsurance on Premiums and Benefits and Claims (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effects of Reinsurance [Line Items]
Direct premium income									$ 18,875	$ 19,592	$ 17,904
Ceded premiums									(566)	(608)	(520)
Assumed premiums earned									222	241	186
Net premium income	$ 4,580	$ 4,648	$ 4,665	$ 4,638	$ 4,778	$ 5,022	$ 4,823	$ 4,602	18,531	19,225	17,570
Direct benefits and claims									12,486	13,240
Benefits and claims, net									12,181	12,919	11,746
All other
Effects of Reinsurance [Line Items]
Ceded premiums									(51)	(48)
Assumed premiums earned									6	7
Ceded benefits and claims									(44)	(38)
Assumed benefits and claims from other companies									3	4
Aflac Japan
Effects of Reinsurance [Line Items]
Net premium income									12,752	13,537	12,046
Benefits and claims, net									9,087	9,828	$ 8,705
Aflac Japan | Closed block
Effects of Reinsurance [Line Items]
Ceded premiums									(515)	(560)
Assumed premiums earned									216	234
Ceded benefits and claims									(473)	(509)
Assumed benefits and claims from other companies									209	222
Intercompany eliminations
Effects of Reinsurance [Line Items]
Ceded benefits and claims									51	58
Assumed benefits and claims from other companies									$ (51)	$ (58)

NOTES PAYABLE - Additional Info

NOTES PAYABLE - Additional Information (Detail) ¥ in Billions	1 Months Ended															12 Months Ended
	Nov. 30, 2017USD ($)	Oct. 31, 2017JPY (¥)	Feb. 28, 2017USD ($)	Jan. 31, 2017JPY (¥)	Dec. 31, 2016USD ($)	Sep. 30, 2016USD ($)series	Mar. 31, 2015USD ($)series	Nov. 30, 2014USD ($)	Jun. 30, 2013USD ($)	Oct. 31, 2012USD ($)	Sep. 30, 2012USD ($)	Jul. 31, 2012USD ($)	Feb. 29, 2012USD ($)series	Aug. 31, 2010USD ($)	Dec. 31, 2009USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2017JPY (¥)	Dec. 31, 2016JPY (¥)	Sep. 30, 2016JPY (¥)series	Mar. 31, 2015JPY (¥)series	Nov. 30, 2014JPY (¥)	Jun. 30, 2013JPY (¥)	Oct. 31, 2012JPY (¥)	Sep. 30, 2012JPY (¥)	Feb. 29, 2012JPY (¥)series
Debt Instrument [Line Items]
Number of series of senior unsecured term loan facilities | series						2														2
Number of series of senior notes issued through a U.S. public debt offering (in series) | series						2	2						2							2	2					2
2.108% subordinated notes due October 2047
Debt Instrument [Line Items]
Debt instrument, interest rate		2.108%														2.108%		2.108%
Debt instrument, term		30 years
Debt Instrument, Redemption, Description		The debentures are redeemable (i) at any time, in whole but not in part, upon the occurrence of certain tax events or certain rating agency events, as specified in the indenture governing the terms of the debentures or (ii) on or after October 23, 2027, in whole or in part, at a redemption price equal to their principal amount plus accrued and unpaid interest to, but excluding, the date of redemption.
Debt Instrument, Call Date, Earliest		Oct. 23, 2027
Debt Instrument, Interest Rate Terms		The debentures bear interest at an initial rate of 2.108% per annum through October 22, 2027, or earlier redemption. Thereafter, the rate of the interest of the debentures will be reset every five years at a rate of interest equal to the then-current JPY 5-year Swap Offered Rate plus 205 basis points.
Debt instrument, principal amount | ¥		¥ 60																¥ 60
.932% senior notes due January 2027
Debt Instrument [Line Items]
Debt instrument, interest rate				0.932%												0.932%		0.932%
Debt instrument, term				10 years
Debt instrument, principal amount | ¥				¥ 60														¥ 60
2.875% senior notes due October 2026
Debt Instrument [Line Items]
Debt instrument, interest rate					2.875%	2.875%										2.875%	2.875%	2.875%	2.875%	2.875%
Debt instrument, term						10 years
Debt instrument, principal amount						$ 300,000,000
4.00% senior notes due October 2046
Debt Instrument [Line Items]
Debt instrument, interest rate					4.00%	4.00%										4.00%	4.00%	4.00%	4.00%	4.00%
Debt instrument, term						30 years
Debt instrument, principal amount						$ 400,000,000
Yen-denominated loans
Debt Instrument [Line Items]
Debt instrument, principal amount | ¥																				¥ 30
Yen-denominated loan variable interest rate due September 2021
Debt Instrument [Line Items]
Debt instrument, interest rate					0.31%											0.32%	0.31%	0.32%	0.31%
Debt Instrument, Description of Variable Rate Basis						Tokyo interbank market rate (TIBOR), or alternate TIBOR, if applicable, plus the applicable TIBOR margin
Debt instrument, term						5 years
Debt Instrument, Interest Rate Terms						bears an interest rate per annum equal to the Tokyo interbank market rate (TIBOR), or alternate TIBOR, if applicable, plus the applicable TIBOR margin and has a five-year maturity. The applicable margin ranges between .20% and .60%, depending on the Parent Company's debt ratings as of the date of determination.
Debt instrument, principal amount | ¥																		¥ 5	¥ 5	5
Yen-denominated loan variable interest rate due September 2023
Debt Instrument [Line Items]
Debt instrument, interest rate					0.46%											0.47%	0.46%	0.47%	0.46%
Debt Instrument, Description of Variable Rate Basis						TIBOR, or alternate TIBOR, if applicable, plus the applicable TIBOR margin
Debt instrument, term						7 years
Debt Instrument, Interest Rate Terms						bears an interest rate per annum equal to TIBOR, or alternate TIBOR, if applicable, plus the applicable TIBOR margin and has a seven-year maturity. The applicable margin ranges between .35% and .75%, depending on the Parent Company's debt ratings as of the date of determination.
Debt instrument, principal amount | ¥																		¥ 25	¥ 25	¥ 25
2.40% senior notes due March 2020
Debt Instrument [Line Items]
Debt instrument, interest rate					2.40%		2.40%									2.40%	2.40%	2.40%	2.40%		2.40%
Debt instrument, term							5 years
Debt instrument effective principal amount after cross currency swap | ¥																					¥ 67
Debt instrument, principal amount							$ 550,000,000									$ 550,000,000
Debt instrument, effective interest rate							0.24%														0.24%
3.25% senior notes due March 2025
Debt Instrument [Line Items]
Debt instrument, interest rate					3.25%		3.25%									3.25%	3.25%	3.25%	3.25%		3.25%
Debt instrument, term							10 years
Debt instrument effective principal amount after cross currency swap | ¥																					¥ 55
Debt instrument, principal amount							$ 450,000,000									$ 450,000,000
Debt instrument, effective interest rate							0.82%														0.82%
3.625% senior notes due November 2024
Debt Instrument [Line Items]
Debt instrument, interest rate					3.625%			3.625%								3.625%	3.625%	3.625%	3.625%			3.625%
Debt instrument, term								10 years
Debt Instrument, Redemption, Description								These notes are redeemable at the Parent Company's option in whole at any time or in part from time to time at a redemption price equal to the greater of: (i) the aggregate principal amount of the notes to be redeemed or (ii) the amount equal to the sum of the present values of the remaining scheduled payments for principal of and interest on the notes to be redeemed, not including any portion of the payments of interest accrued as of such redemption date, discounted to such redemption date on a semiannual basis at the treasury rate plus 20 basis points, plus in each case, accrued and unpaid interest on the principal amount of the notes to be redeemed to, but excluding, such redemption date.
Debt instrument effective principal amount after cross currency swap | ¥																						¥ 85.3
Debt instrument, principal amount								$ 750,000,000								$ 750,000,000
Debt instrument, effective interest rate								1.00%														1.00%
3.625% senior notes due June 2023
Debt Instrument [Line Items]
Debt instrument, interest rate					3.625%				3.625%							3.625%	3.625%	3.625%	3.625%				3.625%
Debt instrument, term									10 years
Debt Instrument, Redemption, Description									These notes are redeemable at the Parent Company's option in whole at any time or in part from time to time at a redemption price equal to the greater of: (i) the aggregate principal amount of the notes to be redeemed or (ii) the amount equal to the sum of the present values of the remaining scheduled payments for principal of and interest on the notes to be redeemed, not including any portion of the payments of interest accrued as of such redemption date, discounted to such redemption date on a semiannual basis at the treasury rate plus 20 basis points, plus in each case, accrued and unpaid interest on the principal amount of the notes to be redeemed to, but excluding, such redemption date.
Debt instrument effective principal amount after cross currency swap | ¥																							¥ 69.8
Debt instrument, principal amount									$ 700,000,000							$ 700,000,000
Debt instrument, effective interest rate									1.50%														1.50%
5.50% subordinated notes due September 2052
Debt Instrument [Line Items]
Repayments of debt	$ 500,000,000
Debt instrument, interest rate	5.50%				5.50%					5.50%	5.50%						5.50%		5.50%					5.50%	5.50%
Debt instrument, term											40 years
Debt instrument effective principal amount after cross currency swap | ¥																								¥ 3.9	¥ 35.3
Debt instrument, principal amount										$ 50,000,000	$ 450,000,000
Debt instrument, effective interest rate										4.42%	4.41%													4.42%	4.41%
Derivative, term of contract										5 years	5 years
Expense on extinguishment of debt	$ 13,000,000															$ 13,000,000
2.65% senior notes paid February 2017
Debt Instrument [Line Items]
Repayments of debt			$ 650,000,000
Debt instrument, interest rate			2.65%		2.65%							2.65%	2.65%				2.65%		2.65%							2.65%
Debt instrument, term												5 years	5 years
Debt instrument effective principal amount after cross currency swap | ¥																										¥ 30.9
Debt instrument, principal amount												$ 250,000,000	$ 400,000,000
Debt instrument, effective interest rate													1.22%													1.22%
4.00% senior notes due February 2022
Debt Instrument [Line Items]
Debt instrument, interest rate					4.00%								4.00%			4.00%	4.00%	4.00%	4.00%							4.00%
Debt instrument, term													10 years
Debt instrument effective principal amount after cross currency swap | ¥																										¥ 27
Debt instrument, principal amount													$ 350,000,000			$ 350,000,000
Debt instrument, effective interest rate													2.07%													2.07%
6.90% senior notes due December 2039
Debt Instrument [Line Items]
Repayments of debt					$ 176,000,000
Debt instrument, interest rate					6.90%											6.90%	6.90%	6.90%	6.90%
Debt instrument, term															30 years
Debt instrument, principal amount															$ 400,000,000
6.45% senior notes due August 2040
Debt Instrument [Line Items]
Repayments of debt					$ 193,000,000
Debt instrument, interest rate					6.45%											6.45%	6.45%	6.45%	6.45%
Debt instrument, term														30 years
Debt instrument, principal amount														$ 450,000,000
Senior Notes due 2039 and 2040
Debt Instrument [Line Items]
Expense on extinguishment of debt																	$ 137,000,000
Senior Notes
Debt Instrument [Line Items]
Debt instrument, principal amount						$ 700,000,000	$ 1,000,000,000						$ 750,000,000
Notes Payable
Debt Instrument [Line Items]
Debt instrument, debt default, amount					$ 0												0
Lower Limit | Yen-denominated loan variable interest rate due September 2021
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate						0.20%
Lower Limit | Yen-denominated loan variable interest rate due September 2023
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate						0.35%
Upper Limit | Yen-denominated loan variable interest rate due September 2021
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate						0.60%
Upper Limit | Yen-denominated loan variable interest rate due September 2023
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate						0.75%
Line of Credit
Debt Instrument [Line Items]
Debt instrument, debt default, amount					$ 0											$ 0	$ 0

NOTES PAYABLE - Summary of Note

NOTES PAYABLE - Summary of Notes Payable (Detail) $ in Millions, ¥ in Billions	Dec. 31, 2017USD ($)		Dec. 31, 2017JPY (¥)	Nov. 30, 2017	Oct. 31, 2017JPY (¥)	Feb. 28, 2017	Jan. 31, 2017JPY (¥)	Dec. 31, 2016USD ($)	Dec. 31, 2016JPY (¥)	Sep. 30, 2016USD ($)	Sep. 30, 2016JPY (¥)	Mar. 31, 2015USD ($)	Nov. 30, 2014USD ($)	Jun. 30, 2013USD ($)	Oct. 31, 2012USD ($)	Sep. 30, 2012USD ($)	Jul. 31, 2012USD ($)	Feb. 29, 2012USD ($)	Aug. 31, 2010USD ($)	Dec. 31, 2009USD ($)
Debt Instrument [Line Items]
Notes payable	$ 5,289							$ 5,360
2.65% senior notes paid February 2017
Debt Instrument [Line Items]
Notes payable	0							$ 649
Debt instrument, principal amount																	$ 250	$ 400
Debt instrument, interest rate						2.65%		2.65%	2.65%								2.65%	2.65%
2.40% senior notes due March 2020
Debt Instrument [Line Items]
Notes payable	548							$ 547
Debt instrument, principal amount	$ 550											$ 550
Debt instrument, interest rate	2.40%		2.40%					2.40%	2.40%			2.40%
4.00% senior notes due February 2022
Debt Instrument [Line Items]
Notes payable	$ 348							$ 348
Debt instrument, principal amount	$ 350																	$ 350
Debt instrument, interest rate	4.00%		4.00%					4.00%	4.00%									4.00%
3.625% senior notes due June 2023
Debt Instrument [Line Items]
Notes payable	$ 697							$ 696
Debt instrument, principal amount	$ 700													$ 700
Debt instrument, interest rate	3.625%		3.625%					3.625%	3.625%					3.625%
3.625% senior notes due November 2024
Debt Instrument [Line Items]
Notes payable	$ 745							$ 745
Debt instrument, principal amount	$ 750												$ 750
Debt instrument, interest rate	3.625%		3.625%					3.625%	3.625%				3.625%
3.25% senior notes due March 2025
Debt Instrument [Line Items]
Notes payable	$ 446							$ 445
Debt instrument, principal amount	$ 450											$ 450
Debt instrument, interest rate	3.25%		3.25%					3.25%	3.25%			3.25%
2.875% senior notes due October 2026
Debt Instrument [Line Items]
Notes payable	$ 297							$ 298
Debt instrument, principal amount										$ 300
Debt instrument, interest rate	2.875%		2.875%					2.875%	2.875%	2.875%	2.875%
6.90% senior notes due December 2039
Debt Instrument [Line Items]
Notes payable	$ 220							$ 220
Debt instrument, principal amount																				$ 400
Debt instrument, interest rate	6.90%		6.90%					6.90%	6.90%
6.45% senior notes due August 2040
Debt Instrument [Line Items]
Notes payable	$ 254							$ 254
Debt instrument, principal amount																			$ 450
Debt instrument, interest rate	6.45%		6.45%					6.45%	6.45%
4.00% senior notes due October 2046
Debt Instrument [Line Items]
Notes payable	$ 394							$ 394
Debt instrument, principal amount										$ 400
Debt instrument, interest rate	4.00%		4.00%					4.00%	4.00%	4.00%	4.00%
5.50% subordinated notes due September 2052
Debt Instrument [Line Items]
Notes payable	$ 0	[1]						$ 486
Debt instrument, principal amount															$ 50	$ 450
Debt instrument, interest rate				5.50%				5.50%	5.50%						5.50%	5.50%
.932% senior notes due January 2027
Debt Instrument [Line Items]
Notes payable	$ 528							$ 0
Debt instrument, principal amount | ¥			¥ 60				¥ 60
Debt instrument, interest rate	0.932%		0.932%				0.932%
2.108% subordinated notes due October 2047
Debt Instrument [Line Items]
Notes payable	$ 526							0
Debt instrument, principal amount | ¥			¥ 60		¥ 60
Debt instrument, interest rate	2.108%		2.108%		2.108%
Yen-denominated loan variable interest rate due September 2021
Debt Instrument [Line Items]
Notes payable	$ 44							$ 43
Debt instrument, principal amount | ¥			¥ 5						¥ 5		¥ 5
Debt instrument, interest rate	0.32%		0.32%					0.31%	0.31%
Yen-denominated loan variable interest rate due September 2023
Debt Instrument [Line Items]
Notes payable	$ 220							$ 214
Debt instrument, principal amount | ¥			¥ 25						¥ 25		¥ 25
Debt instrument, interest rate	0.47%		0.47%					0.46%	0.46%
Capitalized lease obligations
Debt Instrument [Line Items]
Notes payable	$ 22							$ 21
[1]	Redeemed in November 2017

NOTES PAYABLE - Aggregate Contr

NOTES PAYABLE - Aggregate Contractual Maturities of Notes Payable (Detail) $ in Millions	Dec. 31, 2017USD ($)
Debt Instrument [Line Items]
2,018	$ 8
2,019	7
2,020	553
2,021	46
2,022	351
Thereafter	4,365
Total	5,330
Long-term debt
Debt Instrument [Line Items]
2,018	0
2,019	0
2,020	550
2,021	44
2,022	350
Thereafter	4,364
Total	5,308
Capitalized lease obligations
Debt Instrument [Line Items]
2,018	8
2,019	7
2,020	3
2,021	2
2,022	1
Thereafter	1
Total	$ 22

NOTES PAYABLE - Summary of No97

NOTES PAYABLE - Summary of Notes Payable (Parenthetical) (Detail) $ in Millions, ¥ in Billions

1 Months Ended

Oct. 31, 2017JPY (¥)

Jan. 31, 2017JPY (¥)

Sep. 30, 2016USD ($)

Mar. 31, 2015USD ($)

Nov. 30, 2014USD ($)

Jun. 30, 2013USD ($)

Sep. 30, 2012USD ($)

Jul. 31, 2012USD ($)

Feb. 29, 2012USD ($)

Aug. 31, 2010USD ($)

Dec. 31, 2009USD ($)

Dec. 31, 2017USD ($)

Dec. 31, 2017JPY (¥)

Nov. 30, 2017

Feb. 28, 2017

Dec. 31, 2016JPY (¥)

Sep. 30, 2016JPY (¥)

Oct. 31, 2012USD ($)

2.65% senior notes paid February 2017

Debt Instrument [Line Items]

Debt instrument, interest rate

2.65%

2.65%

2.65%

2.65%

Debt instrument, principal amount

$ 250

$ 400

Debt instrument, term

5 years

5 years

2.40% senior notes due March 2020

Debt Instrument [Line Items]

Debt instrument, interest rate

2.40%

2.40%

2.40%

2.40%

Debt instrument, principal amount

$ 550

$ 550

Debt instrument, term

5 years

4.00% senior notes due February 2022

Debt Instrument [Line Items]

Debt instrument, interest rate

4.00%

4.00%

4.00%

4.00%

Debt instrument, principal amount

$ 350

$ 350

Debt instrument, term

10 years

3.625% senior notes due June 2023

Debt Instrument [Line Items]

Debt instrument, interest rate

3.625%

3.625%

3.625%

3.625%

Debt instrument, principal amount

$ 700

$ 700

Debt instrument, term

10 years

3.625% senior notes due November 2024

Debt Instrument [Line Items]

Debt instrument, interest rate

3.625%

3.625%

3.625%

3.625%

Debt instrument, principal amount

$ 750

$ 750

Debt instrument, term

10 years

3.25% senior notes due March 2025

Debt Instrument [Line Items]

Debt instrument, interest rate

3.25%

3.25%

3.25%

3.25%

Debt instrument, principal amount

$ 450

$ 450

Debt instrument, term

10 years

2.875% senior notes due October 2026

Debt Instrument [Line Items]

Debt instrument, interest rate

2.875%

2.875%

2.875%

2.875%

2.875%

Debt instrument, principal amount

$ 300

Debt instrument, term

10 years

6.90% senior notes due December 2039

Debt Instrument [Line Items]

Debt instrument, interest rate

6.90%

6.90%

6.90%

Debt instrument, principal amount

$ 400

Debt instrument, term

30 years

6.45% senior notes due August 2040

Debt Instrument [Line Items]

Debt instrument, interest rate

6.45%

6.45%

6.45%

Debt instrument, principal amount

$ 450

Debt instrument, term

30 years

4.00% senior notes due October 2046

Debt Instrument [Line Items]

Debt instrument, interest rate

4.00%

4.00%

4.00%

4.00%

4.00%

Debt instrument, principal amount

$ 400

Debt instrument, term

30 years

5.50% subordinated notes due September 2052

Debt Instrument [Line Items]

Debt instrument, interest rate

5.50%

5.50%

5.50%

5.50%

Debt instrument, principal amount

$ 450

$ 50

Debt instrument, term

40 years

.932% senior notes due January 2027

Debt Instrument [Line Items]

Debt instrument, interest rate

0.932%

0.932%

0.932%

Debt instrument, principal amount | ¥

¥ 60

¥ 60

Debt instrument, term

10 years

2.108% subordinated notes due October 2047

Debt Instrument [Line Items]

Debt Instrument, Interest Rate Terms

The debentures bear interest at an initial rate of 2.108% per annum through October 22, 2027, or earlier redemption. Thereafter, the rate of the interest of the debentures will be reset every five years at a rate of interest equal to the then-current JPY 5-year Swap Offered Rate plus 205 basis points.

Debt instrument, interest rate

2.108%

2.108%

2.108%

Debt instrument, principal amount | ¥

¥ 60

¥ 60

Debt instrument, term

30 years

Yen-denominated loan variable interest rate due September 2021

Debt Instrument [Line Items]

Debt Instrument, Interest Rate Terms

bears an interest rate per annum equal to the Tokyo interbank market rate (TIBOR), or alternate TIBOR, if applicable, plus the applicable TIBOR margin and has a five-year maturity. The applicable margin ranges between .20% and .60%, depending on the Parent Company's debt ratings as of the date of determination.

Debt Instrument, Description of Variable Rate Basis

Tokyo interbank market rate (TIBOR), or alternate TIBOR, if applicable, plus the applicable TIBOR margin

Debt instrument, interest rate

0.32%

0.32%

0.31%

Debt instrument, principal amount | ¥

¥ 5

¥ 5

¥ 5

Debt instrument, term

5 years

Yen-denominated loan variable interest rate due September 2023

Debt Instrument [Line Items]

Debt Instrument, Interest Rate Terms

bears an interest rate per annum equal to TIBOR, or alternate TIBOR, if applicable, plus the applicable TIBOR margin and has a seven-year maturity. The applicable margin ranges between .35% and .75%, depending on the Parent Company's debt ratings as of the date of determination.

Debt Instrument, Description of Variable Rate Basis

TIBOR, or alternate TIBOR, if applicable, plus the applicable TIBOR margin

Debt instrument, interest rate

0.47%

0.47%

0.46%

Debt instrument, principal amount | ¥

¥ 25

¥ 25

¥ 25

Debt instrument, term

7 years

Upper Limit | Yen-denominated loan variable interest rate due September 2021

Debt Instrument [Line Items]

Debt Instrument, Basis Spread on Variable Rate

0.60%

Upper Limit | Yen-denominated loan variable interest rate due September 2023

Debt Instrument [Line Items]

Debt Instrument, Basis Spread on Variable Rate

0.75%

Lower Limit | Yen-denominated loan variable interest rate due September 2021

Debt Instrument [Line Items]

Debt Instrument, Basis Spread on Variable Rate

0.20%

Lower Limit | Yen-denominated loan variable interest rate due September 2023

Debt Instrument [Line Items]

Debt Instrument, Basis Spread on Variable Rate

0.35%

NOTES PAYABLE - Summary of Line

NOTES PAYABLE - Summary of Lines of Credit (Detail) - 12 months ended Dec. 31, 2017 ¥ in Millions, $ in Millions	USD ($)	JPY (¥)
$100 million line of credit
Line of Credit Facility [Line Items]
Line of credit facility, interest rate description	The rate quoted by the bank and agreed upon at the time of borrowing
Line of credit facility term	364 days
Line of credit facility, maximum borrowing capacity | $	$ 100
Line of credit facility, amount outstanding | $	$ 0
100.0 billion yen line of credit
Line of Credit Facility [Line Items]
Line of credit facility, interest rate description	A rate per annum equal to (a) Tokyo interbank market rate (TIBOR) plus, the alternative applicable TIBOR margin during the availability period from the closing date to the commitment termination date or (b) the TIBOR rate offered by the agent to major banks in yen for the applicable period plus, the applicable alternative TIBOR margin during the term out period
Line of credit facility term	3 years
Line of credit facility, maximum borrowing capacity | ¥		¥ 100,000
Line of credit facility, amount outstanding | ¥		0
55.0 billion yen line of credit
Line of Credit Facility [Line Items]
Line of credit facility, interest rate description	A rate per annum equal to, at the Company's option, either, (a) London Interbank Offered Rate (LIBOR) adjusted for certain costs or (b) a base rate determined by reference to the highest of (1) the federal funds rate plus 1/2 of 1%, (2) the rate of interest for such day announced by Mizuho Bank, Ltd. as its prime rate, or (3) the eurocurrency rate for an interest period of one month plus 1.00%, in each case plus an applicable margin
Line of credit facility term	5 years
Line of credit facility, maximum borrowing capacity | ¥		55,000
Line of credit facility, amount outstanding | ¥		0
$50 million line of credit
Line of Credit Facility [Line Items]
Line of credit facility, interest rate description	A rate per annum equal to, at the Parent Company's option, either (a) a eurocurrency rate determined by reference to the agent's LIBOR for the interest period relevant to such borrowing or (b) the base rate determined by reference to the greater of (i) the prime rate as determined by the agent, and (ii) the sum of 0.50% and the federal funds rate for such day
Line of credit facility, maximum borrowing capacity | $	$ 50
Line of credit facility, amount outstanding | $	$ 0
$250 million line of credit
Line of Credit Facility [Line Items]
Line of credit facility, interest rate description	USD three-month LIBOR plus 75 basis points per annum
Line of credit facility term	364 days
Line of credit facility, maximum borrowing capacity | $	$ 250
Line of credit facility, amount outstanding | $	$ 65
Debt instrument, term	3 months
37.5 billion yen line of credit
Line of Credit Facility [Line Items]
Line of credit facility, interest rate description	Three-month TIBOR plus 80 basis points per annum
Line of credit facility term	364 days
Line of credit facility, maximum borrowing capacity | ¥		37,500
Line of credit facility, amount outstanding | ¥		¥ 0
Debt instrument, term	3 months
Lower Limit | 100.0 billion yen line of credit
Line of Credit Facility [Line Items]
Line of credit facility, commitment fee percentage	0.30%
Lower Limit | 55.0 billion yen line of credit
Line of Credit Facility [Line Items]
Line of credit facility, commitment fee percentage	0.085%
Upper Limit | $100 million line of credit
Line of Credit Facility [Line Items]
Debt instrument, term	3 months
Upper Limit | 100.0 billion yen line of credit
Line of Credit Facility [Line Items]
Line of credit facility, commitment fee percentage	0.50%
Upper Limit | 55.0 billion yen line of credit
Line of Credit Facility [Line Items]
Line of credit facility, commitment fee percentage	0.225%
Upper Limit | $50 million line of credit
Line of Credit Facility [Line Items]
Debt instrument, term	3 months

INCOME TAXES - Additional Infor

INCOME TAXES - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended	3 Months Ended	12 Months Ended
	Jan. 31, 2018	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 22, 2017
Income Taxes [Line Items]
Japan Tax Rate		28.20%	28.20%	28.80%	30.80%
U.S. federal statutory corporate income tax rate			35.00%	35.00%	35.00%
Deferred Tax Assets, Gross		$ 5,916	$ 5,916	$ 5,498
Deferred Tax Liabilities, Gross		9,828	9,828	10,554
Deferred Tax Liabilities, Net		4,569	4,569	5,056
Income Tax Expense, Gross, Continuing Operations, Adjustment of Deferred Tax Assets		1,000
Income Tax Benefit, Gross, Continuing Operations, Adjustment of Deferred Tax Liabilities		2,900
Income Tax Expense (Benefit), Continuing Operations, Adjustment of Deferred Tax (Asset) Liability		1,900
Deferred Tax Assets, Valuation Allowance		(657)	(657)	0
Unrecognized tax benefit, deductibility highly certain, timing uncertain		13	$ 13	293
Non-life operating loss carryforwards, limitations			only 35% of non-life operating losses can be offset against life insurance taxable income each year
Unrecognized tax benefits, permanent uncertainties		1	$ 1
Unrecognized tax benefits, interest and penalties expense			1	13	$ 11
Unrecognized tax benefits, accrued interest and penalties		2	2	$ 26
Capital loss carryforwards		$ 0	$ 0
Aflac Japan
Income Taxes [Line Items]
Deferred Tax Liabilities, Net						$ 4,500
Pre Tax Reform
Income Taxes [Line Items]
Deferred Tax Assets, Gross						6,200
Deferred Tax Liabilities, Gross						12,700
Deferred Tax Liabilities, Net						$ 6,500
Subsequent Event
Income Taxes [Line Items]
U.S. federal statutory corporate income tax rate	21.00%

INCOME TAXES - Components of In

INCOME TAXES - Components of Income Tax Expense (Benefit) Applicable to Pretax Earnings (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of Provision of Income Taxes [Line Items]
Current									$ 631	$ 884	$ 1,288
Deferred									(1,217)	524	41
Total income tax expense	$ (1,585)	$ 359	$ 332	$ 306	$ 402	$ 334	$ 286	$ 386	(586)	1,408	1,329
Aflac U.S.
Reconciliation of Provision of Income Taxes [Line Items]
Current									(91)	234	225
Deferred									(1,193)	388	(1)
Total income tax expense									(1,284)	622	224
Aflac Japan
Reconciliation of Provision of Income Taxes [Line Items]
Current									722	650	1,063
Deferred									(24)	136	42
Total income tax expense									$ 698	$ 786	$ 1,105

INCOME TAXES - Principal Reason

INCOME TAXES - Principal Reasons for Differences and Related Tax Effects where Income Tax Expense Varies from Amount Computed by Applying Expected United States Tax Rate of Thirty Five Percent to Pretax Earnings (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Income taxes based on U.S. statutory rates									$ 1,406	$ 1,424	$ 1,352
Write-down of U.S. deferred tax liabilities for tax reform change									(1,933)	0	0
Utilization of foreign tax credit									(27)	(30)	(27)
Nondeductible expenses									10	8	3
Other, net									(42)	6	1
Total income tax expense	$ (1,585)	$ 359	$ 332	$ 306	$ 402	$ 334	$ 286	$ 386	$ (586)	$ 1,408	$ 1,329

INCOME TAXES - Total Income Tax

INCOME TAXES - Total Income Tax Expense (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Statements of earnings	$ (1,585)	$ 359	$ 332	$ 306	$ 402	$ 334	$ 286	$ 386	$ (586)	$ 1,408	$ 1,329
Other comprehensive income (loss):
Unrealized foreign currency translation gains (losses) during period									52	70	16
Unrealized gains (losses) on investment securities:
Unrealized holding gains (losses) on investment securities during period									575	962	(931)
Reclassification adjustment for realized (gains) losses on investment securities included in net earnings									1	18	21
Unrealized gains (losses) on derivatives during period									0	1	0
Pension liability adjustment during period									3	(16)	(7)
Total income tax expense (benefit) related to items of other comprehensive income (loss)									631	1,035	(901)
Additional paid-in capital (exercise of stock options)									0	(10)	4
Total income taxes									$ 45	$ 2,433	$ 432

INCOME TAXES - Income Tax Effec

INCOME TAXES - Income Tax Effects of Temporary Differences that Gave Rise to Deferred Income Tax Assets and Liabilities (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Deferred income tax liabilities:
Deferred policy acquisition costs	$ 3,285	$ 4,065
Unrealized gains and other basis differences on investment securities	2,882	3,056
Premiums receivable	104	130
Policy benefit reserves	3,557	3,303
Total deferred income tax liabilities	9,828	10,554
Deferred income tax assets:
Unfunded retirement benefits	8	13
Other accrued expenses	141	39
Policy and contract claims	870	792
Foreign currency loss on Japan branch	67	185
Deferred compensation	155	243
Capital loss carryforwards	0	3
Depreciation	114	88
Anticipatory foreign tax credit	4,504	4,028
Other	57	107
Total deferred income tax assets before valuation allowance	5,916	5,498
Valuation allowance	(657)	0
Total deferred income tax assets after valuation allowance	5,259	5,498
Net deferred income tax liability	4,569	5,056
Current income tax liability	176	331
Total income tax liability	$ 4,745	$ 5,387

INCOME TAXES - Reconciliation o

INCOME TAXES - Reconciliation of Beginning and Ending Amount of Unrecognized Tax Benefits (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance, beginning of year	$ 294	$ 264
Additions for tax positions of prior years	0	33
Reductions for tax positions of prior years	(280)	(3)
Balance, end of year	$ 14	$ 294

SHAREHOLDERS' EQUITY - Addition

SHAREHOLDERS' EQUITY - Additional Information (Detail) shares in Millions	12 Months Ended
	Dec. 31, 2017Voteshares	Dec. 31, 2016shares	Dec. 31, 2015shares	Aug. 31, 2017shares
Stockholders Equity Note [Line Items]
Common stock, voting rights	are generally entitled to one vote per share until they have been held by the same beneficial owner for a continuous period of 48 months, at which time they become entitled to 10 votes per share.
Remaining common stock available for purchase under share repurchase authorizations	49
Common stock votes per share | Vote	1
Share Repurchase Program
Stockholders Equity Note [Line Items]
Stock Acquired In Open Market, Shares	17.8	21.6	21.2
Share Repurchase Authorization 2017
Stockholders Equity Note [Line Items]
Stock Repurchase Program, Number of Shares Authorized to be Repurchased				40
Share Held For Continuous Forty Eight Month Period
Stockholders Equity Note [Line Items]
Voting rights, votes per share | Vote	10

SHAREHOLDERS' EQUITY - Reconcil

SHAREHOLDERS' EQUITY - Reconciliation of Number of Shares of Common Stock (Detail) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Common Stock Issued [Roll Forward]
Balance, beginning of period	671,249	669,723	668,132
Exercise of stock options and issuance of restricted shares	1,632	1,526	1,591
Balance, end of period	672,881	671,249	669,723
Treasury Stock [Roll Forward]
Balance, beginning of period	265,439	245,343	225,687
Exercise of stock options	(2,883)	(2,061)	(2,013)
Balance, end of period	282,426	265,439	245,343
Shares outstanding, end of period	390,455	405,810	424,380
Treasury Stock
Treasury Stock [Roll Forward]
Stock Acquired In Open Market, Shares	17,755	21,618	21,179
Other purchases	509	330	247
Shares issued to AFL Stock Plan	(891)	(1,064)	(1,209)
Exercise of stock options	(367)	(683)	(465)
Other dispositions	(19)	(105)	(96)

SHAREHOLDERS' EQUITY - Anti-Dil

SHAREHOLDERS' EQUITY - Anti-Dilutive Share-Based Awards Excluded from Calculation of Diluted Earnings Per Share (Detail) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stockholders' Equity Note [Abstract]
Anti-dilutive share-based awards	255	911	1,862

SHAREHOLDERS' EQUITY - Weighted

SHAREHOLDERS' EQUITY - Weighted-Average Shares Used in Calculating Earnings Per Share (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stockholders' Equity Note [Abstract]
Weighted-average outstanding shares used for calculating basic EPS	396,021	411,471	430,654
Dilutive effect of share-based awards	2,909	2,450	2,518
Weighted-average outstanding shares used for calculating diluted EPS	398,930	413,921	433,172

SHAREHOLDERS' EQUITY - Changes

SHAREHOLDERS' EQUITY - Changes in Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income [Roll Forward]
Balance, beginning of period	[1]	$ 2,630	$ 625	$ 1,979
Other comprehensive income loss before reclassifications net of tax	[1]	1,386	2,037	(1,314)
Amounts reclassified from accumulated other comprehensive income net of tax	[1]	12	(32)	(40)
Other comprehensive income (loss), net of income taxes	[1]	1,398	2,005	(1,354)
Balance, end of period	[1]	4,028	2,630	625
Unrealized foreign currency translation gains (losses)
Accumulated Other Comprehensive Income [Roll Forward]
Balance, beginning of period	[1]	(1,983)	(2,196)	(2,541)
Other comprehensive income loss before reclassifications net of tax	[1]	233	213	345
Amounts reclassified from accumulated other comprehensive income net of tax	[1]	0	0	0
Other comprehensive income (loss), net of income taxes	[1]	233	213	345
Balance, end of period	[1]	(1,750)	(1,983)	(2,196)
Unrealized gains (losses) on investment securities
Accumulated Other Comprehensive Income [Roll Forward]
Balance, beginning of period	[1]	4,805	2,986	4,672
Other comprehensive income loss before reclassifications net of tax	[1]	1,158	1,854	(1,646)
Amounts reclassified from accumulated other comprehensive income net of tax	[1]	1	(35)	(40)
Other comprehensive income (loss), net of income taxes	[1]	1,159	1,819	(1,686)
Balance, end of period	[1]	5,964	4,805	2,986
Unrealized Gains (Losses) on Derivatives
Accumulated Other Comprehensive Income [Roll Forward]
Balance, beginning of period	[1]	(24)	(26)	(26)
Other comprehensive income loss before reclassifications net of tax	[1]	1	2	0
Amounts reclassified from accumulated other comprehensive income net of tax	[1]	0	0	0
Other comprehensive income (loss), net of income taxes	[1]	1	2	0
Balance, end of period	[1]	(23)	(24)	(26)
Pension liability adjustment
Accumulated Other Comprehensive Income [Roll Forward]
Balance, beginning of period	[1]	(168)	(139)	(126)
Other comprehensive income loss before reclassifications net of tax	[1]	(6)	(32)	(13)
Amounts reclassified from accumulated other comprehensive income net of tax	[1]	11	3	0
Other comprehensive income (loss), net of income taxes	[1]	5	(29)	(13)
Balance, end of period	[1]	$ (163)	$ (168)	$ (139)
[1]	All amounts in the table above are net of tax.

SHAREHOLDERS' EQUITY - Reclassi

SHAREHOLDERS' EQUITY - Reclassifications Out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Sales and redemptions										$ 28	$ 141	$ 302
Other-than-temporary impairment losses realized										(37)	(85)	(154)
Total before tax		$ 999	$ 1,075	$ 1,045	$ 898	$ 1,153	$ 963	$ 834	$ 1,117	4,018	4,067	3,862
Income Tax (Expense) Benefit		$ 1,585	$ (359)	$ (332)	$ (306)	$ (402)	$ (334)	$ (286)	$ (386)	586	(1,408)	(1,329)
Net of tax										$ 4,604	$ 2,659	$ 2,533
The expected U.S. tax rate										35.00%	35.00%	35.00%
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net of tax										$ (12)	$ 32	$ 40
Reclassification out of Accumulated Other Comprehensive Income | Unrealized gains (losses) on investment securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Sales and redemptions										27	136	214
Other-than-temporary impairment losses realized										(29)	(83)	(153)
Total before tax										(2)	53	61
Income Tax (Expense) Benefit	[1]									1	(18)	(21)
Net of tax										(1)	35	40
Reclassification out of Accumulated Other Comprehensive Income | Pension liability adjustment
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Acquisition and operating expense, actuarial gains (losses)	[2]									(17)	(15)	(17)
Acquisition and operating expenses, prior service (cost) credit	[2]									0	11	17
Income Tax (Expense) Benefit	[1]									6	1	0
Net of tax										$ (11)	$ (3)	$ 0
[1]	Based on 35% tax rate
[2]	These accumulated other comprehensive income components are included in the computation of net periodic pension cost (see Note 14 for additional details).

SHARE-BASED COMPENSATION - Addi

SHARE-BASED COMPENSATION - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	1 Months Ended	12 Months Ended
	Feb. 28, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation arrangement by share based payment award, options, grants in period, weighted average grant date fair value		$ 15.28	$ 12.70	$ 9.46
Closing common stock price		$ 87.78
Aggregate intrinsic value of stock options outstanding		$ 116
Options Outstanding - Weighted-Average Remaining Term (Yrs)		5 years 4 months 24 days
In-the-money stock options exercisable		2,000
Aggregate intrinsic value of stock options exercisable		$ 78
Weighted-average remaining term of stock options exercisable (in years)		3 years 7 months 6 days
Long-Term Incentive Plan Member
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, maximum number of shares issuable		37,500
Share-based compensation arrangement by share-based payment award, maximum number of shares issuable other than options and stock appreciation		19,000
Shares available for future grants under the long-term incentive plan		20,600
Long-term incentive plan awards, term (in years)		10 years
Long-term incentive plan, vesting period		3 years
Restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock awards, grants in period		559	878	638
Total compensation cost not yet recognized, restricted stock awards		$ 32
Share-based compensation arrangement by share-based payment award, equity instruments other than options, nonvested, number of shares		1,817	1,868	1,815	1,880
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition		1 year
Performance Based Vesting Condition Member | Restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Long-term incentive plan, vesting period	3 years
Restricted stock awards, grants in period	253
Percentage of Target Award Opportunities Minimum		0.00%
Percentage of Target Award Opportunities Maximum		200.00%
Total compensation cost not yet recognized, restricted stock awards		$ 12
Share-based compensation arrangement by share-based payment award, equity instruments other than options, nonvested, number of shares		377

SHARE-BASED COMPENSATION - Expe

SHARE-BASED COMPENSATION - Expense Recognized in Connection with Share-Based Awards (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Earnings before income taxes	$ 999	$ 1,075	$ 1,045	$ 898	$ 1,153	$ 963	$ 834	$ 1,117	$ 4,018	$ 4,067	$ 3,862
Net earnings									$ 4,604	$ 2,659	$ 2,533
Net earnings per share:
Basic (in dollars per share)	$ 6.59	$ 1.81	$ 1.80	$ 1.48	$ 1.85	$ 1.54	$ 1.33	$ 1.75	$ 11.63	$ 6.46	$ 5.88
Diluted (in dollars per share)	$ 6.54	$ 1.80	$ 1.79	$ 1.47	$ 1.84	$ 1.53	$ 1.32	$ 1.74	$ 11.54	$ 6.42	$ 5.85
Share Based Compensation Expense
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Earnings from continuing operations									$ 51	$ 68	$ 39
Earnings before income taxes									51	68	39
Net earnings									$ 35	$ 46	$ 27
Net earnings per share:
Basic (in dollars per share)									$ 0.09	$ 0.11	$ 0.06
Diluted (in dollars per share)									$ 0.09	$ 0.11	$ 0.06

SHARE-BASED COMPENSATION - Assu

SHARE-BASED COMPENSATION - Assumptions Used in Valuing Options Granted (Detail) - Employee stock option	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Line Items]
Expected term (years)	5 years 10 months 24 days	6 years 4 months 24 days	6 years 3 months 18 days
Expected volatility	26.00%	27.00%	20.00%
Annual forfeiture rate	3.40%	3.20%	2.80%
Risk-free interest rate	2.50%	2.20%	2.00%
Dividend yield	2.50%	2.90%	2.70%

SHARE-BASED COMPENSATION - Stoc

SHARE-BASED COMPENSATION - Stock Option Activity (Detail) - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stock Option Shares
Beginning Balance	6,340	7,918	9,307
Granted	313	664	855
Canceled	(118)	(181)	(231)
Exercised	(2,883)	(2,061)	(2,013)
Ending Balance	3,652	6,340	7,918
Weighted-Average Exercise Price Per Share
Beginning Balance	$ 52.56	$ 50.94	$ 48.84
Granted	71.60	61.39	61.47
Canceled	49.90	55.63	55.70
Exercised	60.22	48.91	45.15
Ending Balance	$ 56.05	$ 52.56	$ 50.94

SHARE-BASED COMPENSATION - Shar

SHARE-BASED COMPENSATION - Shares Exercisable (Detail) - shares shares in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Shares exercisable, end of year	2,104	4,493	6,085

SHARE-BASED COMPENSATION - S116

SHARE-BASED COMPENSATION - Stock Options Outstanding and Exercisable (Detail) - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices Per Share - Lower Range	$ 22.13
Range of Exercise Prices Per Share - Upper Range	$ 87.71
Options Outstanding - Stock Option Shares	3,652	6,340	7,918	9,307
Options Outstanding - Weighted-Average Remaining Term (Yrs)	5 years 4 months 24 days
Options Outstanding - Weighted-Average Exercise Price Per Share	$ 56.05	$ 52.56	$ 50.94	$ 48.84
Options Exercisable - Stock Option Shares	2,104	4,493	6,085
Options Exercisable - Weighted-Average Exercise Price Per Share	$ 50.67
$22.13 - $48.56
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices Per Share - Lower Range	22.13
Range of Exercise Prices Per Share - Upper Range	$ 48.56
Options Outstanding - Stock Option Shares	823
Options Outstanding - Weighted-Average Remaining Term (Yrs)	2 years 6 months
Options Outstanding - Weighted-Average Exercise Price Per Share	$ 38.56
Options Exercisable - Stock Option Shares	823
Options Exercisable - Weighted-Average Exercise Price Per Share	$ 38.56
$49.50 - $57.93
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices Per Share - Lower Range	49.50
Range of Exercise Prices Per Share - Upper Range	$ 57.93
Options Outstanding - Stock Option Shares	1,034
Options Outstanding - Weighted-Average Remaining Term (Yrs)	5 years 6 months
Options Outstanding - Weighted-Average Exercise Price Per Share	$ 55.64
Options Exercisable - Stock Option Shares	608
Options Exercisable - Weighted-Average Exercise Price Per Share	$ 54.04
$58.08 - $61.81
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices Per Share - Lower Range	58.08
Range of Exercise Prices Per Share - Upper Range	$ 61.81
Options Outstanding - Stock Option Shares	748
Options Outstanding - Weighted-Average Remaining Term (Yrs)	5 years 6 months
Options Outstanding - Weighted-Average Exercise Price Per Share	$ 61.29
Options Exercisable - Stock Option Shares	234
Options Exercisable - Weighted-Average Exercise Price Per Share	$ 61.22
$61.95 - $71.04
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices Per Share - Lower Range	61.95
Range of Exercise Prices Per Share - Upper Range	$ 71.04
Options Outstanding - Stock Option Shares	944
Options Outstanding - Weighted-Average Remaining Term (Yrs)	7 years 4 months 24 days
Options Outstanding - Weighted-Average Exercise Price Per Share	$ 65.69
Options Exercisable - Stock Option Shares	439
Options Exercisable - Weighted-Average Exercise Price Per Share	$ 63.06
$71.84 - $87.71
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices Per Share - Lower Range	71.84
Range of Exercise Prices Per Share - Upper Range	$ 87.71
Options Outstanding - Stock Option Shares	103
Options Outstanding - Weighted-Average Remaining Term (Yrs)	9 years
Options Outstanding - Weighted-Average Exercise Price Per Share	$ 73.53
Options Exercisable - Stock Option Shares	0
Options Exercisable - Weighted-Average Exercise Price Per Share	$ 0

SHARE-BASED COMPENSATION - Key

SHARE-BASED COMPENSATION - Key Assumptions Used to Value PBRS (Details) - Performance Based Vesting Condition Member - Restricted stock	12 Months Ended
	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility (based on Aflac Inc. and peer group historical daily stock price)	16.59%
Expected life from grant date (years)	2 years 10 months 24 days
Risk-free interest rate (based on U.S. Treasury yields at the date of grant)	1.56%

SHARE-BASED COMPENSATION - Summ

SHARE-BASED COMPENSATION - Summary of Stock Option Activity (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Total intrinsic value of options exercised	$ 87	$ 41	$ 36
Cash received from options exercised	58	68	68
Tax benefit realized as a result of options exercised and restricted stock releases	$ 74	$ 45	$ 25

SHARE-BASED COMPENSATION - Rest

SHARE-BASED COMPENSATION - Restricted Stock Activity (Detail) - Restricted stock - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Shares
Beginning balance	1,868	1,815	1,880
Granted	559	878	638
Canceled	(101)	(76)	(145)
Vested	(509)	(749)	(558)
Ending Balance	1,817	1,868	1,815
Weighted-Average Grant-Date Fair Value Per Share
Beginning balance	$ 61.76	$ 58.42	$ 54.33
Granted	72.95	61.68	61.51
Canceled	64.45	60.65	57.52
Vested	62.17	53.68	48.41
Ending Balance	$ 64.80	$ 61.76	$ 58.42

STATUTORY ACCOUNTING AND DIV120

STATUTORY ACCOUNTING AND DIVIDEND RESTRICTIONS - Additional Information (Detail) $ in Millions, ¥ in Billions	12 Months Ended
	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2017JPY (¥)
Statutory Accounting Practices [Line Items]
Statutory accounting practices, statutory capital and surplus required	$ 1,400
Net Derivatives Notional Amount	25,751	$ 43,927
Aflac
Statutory Accounting Practices [Line Items]
Net Income, Nebraska state basis	2,600	2,800	$ 2,300
Capital and surplus, statutory accounting practices of the state or country basis	11,001	11,221
Amount available for dividend distribution without prior approval from regulatory agency	2,600
Dividends declared	2,600
Aflac Japan
Statutory Accounting Practices [Line Items]
Capital and surplus, statutory accounting practices of the state or country basis	6,700	$ 5,600
Twenty Seventeen profit repatriation
Statutory Accounting Practices [Line Items]
Intercompany transfer profit repatriation, reduction in amount received	$ 1
Foreign currency forwards and options | Twenty Seventeen profit repatriation
Statutory Accounting Practices [Line Items]
Net Derivatives Notional Amount | ¥				¥ 90.9
Foreign currency forwards and options | Future profit repatriation
Statutory Accounting Practices [Line Items]
Net Derivatives Notional Amount | ¥				¥ 49.5

STATUTORY ACCOUNTING AND DIV121

STATUTORY ACCOUNTING AND DIVIDEND RESTRICTIONS - Reconciliation of Capital and Surplus Between Sap and Practices Permitted by the State of Nebraska (Detail) - Aflac - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Statutory Accounting Practices [Line Items]
Capital and surplus, Nebraska state basis	$ 11,001	$ 11,221
Capital and surplus, NAIC basis	10,140	10,417
Lease Deposits
Statutory Accounting Practices [Line Items]
State permitted practice amount	(43)	(40)
Reinsurance
Statutory Accounting Practices [Line Items]
State permitted practice amount	$ (818)	$ (764)

STATUTORY ACCOUNTING AND DIV122

STATUTORY ACCOUNTING AND DIVIDEND RESTRICTIONS - Profits Repatriated by Aflac Japan to Aflac U.S. (Detail) $ in Millions, ¥ in Billions	12 Months Ended
	Dec. 31, 2017USD ($)	Dec. 31, 2017JPY (¥)	Dec. 31, 2016USD ($)	Dec. 31, 2016JPY (¥)	Dec. 31, 2015USD ($)	Dec. 31, 2015JPY (¥)
Insurance [Abstract]
Profit repatriation	$ 1,150	¥ 129.3	$ 1,286	¥ 138.5	$ 2,139	¥ 259

BENEFIT PLANS - Additional Info

BENEFIT PLANS - Additional Information (Detail) - USD ($) shares in Millions	1 Months Ended	12 Months Ended
	Jan. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2013
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amount of years left to meet rule of 80 for active employees to be eligible for postretirement medical benefits					5 years
Amount of years left to meet 15 year service requirement for active employees age 55 or older to be eligible for postretirement medical benefits					5 years
Net periodic (benefit) cost, excluding service cost		$ 35,000,000	$ 17,000,000	$ (5,000,000)
Transition obligation		$ 0
Percentage of matching contributions by the Company to employee's contributions to 401(k) plan		50.00%	50.00%	50.00%
Non-Elective Defined Contribution Percentage of Employee Compensation		2.00%
Matching 401(k) plan contributions included in acquisition and operating expenses		$ 15,000,000	$ 11,000,000	$ 9,000,000
Shares of employer-issued common stock held for plan participants by plan trustee (in millions)		1
Subsequent Event
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Percentage of matching contributions by the Company to employee's contributions to 401(k) plan	100.00%
Defined Contribution Plan, Special Contribution, Per Employee	$ 500
Lower Limit
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Health care plan, retirement age and years of service combined years for eligibility					80 years
Health care plan, retirement age for eligibility, (in years)					55 years
Health care plan, number of years of service for eligibility					15 years
Upper Limit
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Percentage of matching contributions by the Company to employee's contributions to 401(k) plan		6.00%	6.00%	6.00%
Upper Limit | Subsequent Event
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Percentage of matching contributions by the Company to employee's contributions to 401(k) plan	4.00%
Other Postretirement Benefit Plans, Defined Benefit
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, future amortization of actuarial losses		$ 1,000,000
Associate Stock Bonus Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Deferred policy acquisition costs, amount attributable to stock bonus plan		$ 31,000,000	$ 31,000,000	$ 34,000,000
Japan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
AA corporate bonds average duration		20 years
Japan | Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, future amortization of actuarial losses		$ 1,000,000
Defined benefit plan, expected contributions to the plan in the following year		$ 34,000,000
U.S.
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
AA corporate bonds average duration		17 years
U.S. | Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, future amortization of actuarial losses		$ 16,000,000
Defined benefit plan, expected contributions to the plan in the following year		$ 10,000,000

BENEFIT PLANS - Reconciliation

BENEFIT PLANS - Reconciliation of Funded Status of Basic Employee Defined-Benefit Pension Plans (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Postretirement Benefit Plans, Defined Benefit
Projected benefit obligation:
Benefit obligation, beginning of year		$ 37	$ 40
Service cost		0	1	$ 1
Interest cost		1	2	2
Actuarial (gain) loss		0	(4)
Benefits and expenses paid		(2)	(2)
Effect of foreign exchange rate changes		0	0
Benefit obligation, end of year		36	37	40
Plan assets:
Fair value of plan assets, beginning of year		0	0
Actual return on plan assets		0	0
Employer contributions		2	2
Benefits and expenses paid		(2)	(2)
Effect of foreign exchange rate changes		0	0
Fair value of plan assets, end of year		0	0	0
Funded status of the plans	[1]	(36)	(37)
Amounts recognized in accumulated other comprehensive income:
Net actuarial (gain) loss		6	7
Prior service (credit) cost		0	0
Total included in accumulated other comprehensive income		6	7
Japan | Pension Plan
Projected benefit obligation:
Benefit obligation, beginning of year		329	276
Service cost		20	16	15
Interest cost		6	9	1
Actuarial (gain) loss		(10)	29
Benefits and expenses paid		(14)	(8)
Effect of foreign exchange rate changes		10	7
Benefit obligation, end of year		341	329	276
Plan assets:
Fair value of plan assets, beginning of year		229	198
Actual return on plan assets		16	9
Employer contributions		32	25
Benefits and expenses paid		(14)	(8)
Effect of foreign exchange rate changes		7	5
Fair value of plan assets, end of year		270	229	198
Funded status of the plans	[1]	(71)	(100)
Amounts recognized in accumulated other comprehensive income:
Net actuarial (gain) loss		44	67
Prior service (credit) cost		(2)	(2)
Total included in accumulated other comprehensive income		42	65
Accumulated benefit obligation		307	288
U.S. | Pension Plan
Projected benefit obligation:
Benefit obligation, beginning of year		798	735
Service cost		24	23	23
Interest cost		40	29	18
Actuarial (gain) loss		65	29
Benefits and expenses paid		(19)	(18)
Effect of foreign exchange rate changes		0	0
Benefit obligation, end of year		908	798	735
Plan assets:
Fair value of plan assets, beginning of year		359	336
Actual return on plan assets		61	24
Employer contributions		47	17
Benefits and expenses paid		(19)	(18)
Effect of foreign exchange rate changes		0	0
Fair value of plan assets, end of year		448	359	$ 336
Funded status of the plans	[1]	(460)	(439)
Amounts recognized in accumulated other comprehensive income:
Net actuarial (gain) loss		203	189
Prior service (credit) cost		(4)	(4)
Total included in accumulated other comprehensive income		199	185
Accumulated benefit obligation		$ 756	$ 670
[1]	Recognized in other liabilities in the consolidated balance sheets

BENEFIT PLANS - Weighted-Averag

BENEFIT PLANS - Weighted-Average Actuarial Assumptions (Detail)		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Postretirement Benefit Plans, Defined Benefit
Weighted-average actuarial assumptions:
Discount rate - net periodic benefit cost		4.25%	4.50%	4.50%
Discount rate - benefit obligations		3.75%	4.25%	4.50%
Health care cost trend rates	[1]	5.40%	5.20%	5.30%
Defined benefit plan, ultimate health care cost trend rate		4.50%	4.50%	4.50%
Defined benefit plan number of years that rate reaches ultimate trend rate		77 years	74 years	78 years
Japan | Pension Plan
Weighted-average actuarial assumptions:
Discount rate - net periodic benefit cost		1.25%	1.75%	1.75%
Discount rate - benefit obligations		1.25%	1.25%	1.75%
Expected long-term return on plan assets		2.00%	2.00%	2.00%
U.S. | Pension Plan
Weighted-average actuarial assumptions:
Discount rate - net periodic benefit cost		4.25%	4.50%	4.50%
Discount rate - benefit obligations		3.75%	4.25%	4.50%
Expected long-term return on plan assets		6.75%	7.00%	7.25%
Rate of compensation increase		4.00%	4.00%	4.00%
[1]	For the years 2017, 2016 and 2015, the health care cost trend rates are expected to trend down to 4.5% in 77 years, 4.5% in 74 years, and 4.5% in 78 years, respectively.

BENEFIT PLANS - One-Percentage

BENEFIT PLANS - One-Percentage Point Increase and Decrease in Assumed Health Care Cost Trend Rates (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract]
Increase in total service and interest costs	$ 0
Increase in postretirement benefit obligation	2
Decrease in total service and interest costs	0
Decrease in postretirement benefit obligation	$ 2

BENEFIT PLANS - Net Periodic (B

BENEFIT PLANS - Net Periodic (Benefit) Cost Included in Acquisition and Operating Expenses (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Postretirement Benefit Plans, Defined Benefit
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 0	$ 1	$ 1
Interest cost	1	2	2
Expected return on plan assets	0	0	0
Amortization of net actuarial loss	1	1	2
Amortization of prior service cost (credit)	0	(11)	(17)
Net periodic (benefit) cost	2	(7)	(12)
Japan | Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	20	16	15
Interest cost	6	9	1
Expected return on plan assets	(5)	(4)	(4)
Amortization of net actuarial loss	2	1	1
Amortization of prior service cost (credit)	0	0	0
Net periodic (benefit) cost	23	22	13
U.S. | Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	24	23	23
Interest cost	40	29	18
Expected return on plan assets	(24)	(23)	(22)
Amortization of net actuarial loss	14	13	14
Amortization of prior service cost (credit)	0	0	0
Net periodic (benefit) cost	$ 54	$ 42	$ 33

BENEFIT PLANS - Summary of Amou

BENEFIT PLANS - Summary of Amounts Recognized in Other Comprehensive Loss (Income) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Postretirement Benefit Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss (gain)	$ 0	$ (4)	$ (5)
Amortization of net actuarial loss	(1)	(1)	(2)
Amortization of prior service cost	0	11	17
Total	(1)	6	10
Japan | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss (gain)	(21)	26	3
Amortization of net actuarial loss	(2)	(1)	(1)
Amortization of prior service cost	0	0	0
Total	(23)	25	2
U.S. | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss (gain)	28	27	22
Amortization of net actuarial loss	(14)	(13)	(14)
Amortization of prior service cost	0	0	0
Total	$ 14	$ 14	$ 8

BENEFIT PLANS - Expected Benefi

BENEFIT PLANS - Expected Benefit Payments (Detail) $ in Millions	Dec. 31, 2017USD ($)
Other Postretirement Benefit Plans, Defined Benefit
Schedule of Postemployment Expected Future Benefit Payments [Line Items]
2,018	$ 2
2,019	3
2,020	3
2,021	3
2,022	3
2023-2027	17
Japan | Pension Plan
Schedule of Postemployment Expected Future Benefit Payments [Line Items]
2,018	10
2,019	11
2,020	12
2,021	12
2,022	18
2023-2027	82
U.S. | Pension Plan
Schedule of Postemployment Expected Future Benefit Payments [Line Items]
2,018	23
2,019	24
2,020	25
2,021	26
2,022	35
2023-2027	$ 184

BENEFIT PLANS - Asset Allocatio

BENEFIT PLANS - Asset Allocation Targets (Detail) - Pension Plan	Dec. 31, 2017
Japan
Defined Benefit Plan Disclosure [Line Items]
Asset allocation targets	100.00%
U.S.
Defined Benefit Plan Disclosure [Line Items]
Asset allocation targets	100.00%
Domestic equity securities | Japan
Defined Benefit Plan Disclosure [Line Items]
Asset allocation targets	11.00%
Domestic equity securities | U.S.
Defined Benefit Plan Disclosure [Line Items]
Asset allocation targets	40.00%
International equity securities | Japan
Defined Benefit Plan Disclosure [Line Items]
Asset allocation targets	15.00%
International equity securities | U.S.
Defined Benefit Plan Disclosure [Line Items]
Asset allocation targets	20.00%
Fixed income bond funds | Japan
Defined Benefit Plan Disclosure [Line Items]
Asset allocation targets	59.00%
Fixed income bond funds | U.S.
Defined Benefit Plan Disclosure [Line Items]
Asset allocation targets	40.00%
Other Investments | Japan
Defined Benefit Plan Disclosure [Line Items]
Asset allocation targets	15.00%
Other Investments | U.S.
Defined Benefit Plan Disclosure [Line Items]
Asset allocation targets	0.00%

BENEFIT PLANS - Fair Value Hier

BENEFIT PLANS - Fair Value Hierarchy Levels of Funded Pension Plans' Assets (Detail) - Pension Plan - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Japan
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	$ 270	$ 229	$ 198
U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	448	359	$ 336
U.S. | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	448	359
Japanese equity securities | Japan | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	37	28
International equity securities | Japan | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	50	40
Japanese bonds | Japan | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	91	79
International bonds | Japan | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	62	55
Insurance contracts | Japan | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	30	27
Cash and cash equivalents | Japan | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Cash and cash equivalents | U.S. | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	1	1
U.S. large cap equity securities | U.S. | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	124	104
U.S. mid cap equity securities | U.S. | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	22	19
Real estate equity funds | U.S. | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	13	10
International equity fund | U.S. | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	108	85
Fixed income bond funds | U.S. | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	175	136
Aflac Incorporated common stock | U.S. | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	$ 5	$ 4

COMMITMENTS AND CONTINGENT L132

COMMITMENTS AND CONTINGENT LIABILITIES - Additional Information (Detail) $ in Millions, ¥ in Billions	3 Months Ended	12 Months Ended
	Mar. 31, 2017USD ($)	Dec. 31, 2017USD ($)agreements	Dec. 31, 2017JPY (¥)agreements
Commitments and Contingencies Disclosure [Line Items]
Number of operating service agreements, technology and consulting | agreements		2	2
Number of operating service agreements, management consulting and technology | agreements		1	1
Number of operating service agreements, information technology and data services | agreements		2	2
Operating Leases, lease terms		expire in various years through 2028	expire in various years through 2028
Loss contingency accrual, insurance-related assessment, discount rate	4.25%
Loss contingency, discounted amount of insurance-related assessment liability	$ 62
Loss contingency, undiscounted amount of insurance-related assessment liability	94
Loss contingency, insurance related assessment, discounted amount of premium tax offset	48
Loss contingency, insurance-related assessment, undiscounted amount of premium tax offset	$ 74
Loss contingency, discounted amount of insurance-related assessment liability, realization period for associated asset offsets (in years)	5
Loss contingency, loss in period	$ 14
Mainframe and server computer operations and support
Commitments and Contingencies Disclosure [Line Items]
Outsourcing agreements, remaining term		3 years	3 years
Outsourcing agreements, aggregate remaining cost		$ 243	¥ 27.5
Technology and consulting company application maintenance and development services
Commitments and Contingencies Disclosure [Line Items]
Outsourcing agreements, remaining term		4 years	4 years
Outsourcing agreements, aggregate remaining cost		$ 80	¥ 9
Management consulting and technology services company application maintenance and development services
Commitments and Contingencies Disclosure [Line Items]
Outsourcing agreements, remaining term		4 years	4 years
Outsourcing agreements, aggregate remaining cost		$ 124	¥ 14
Information technology and data services company application maintenance and development services first agreement
Commitments and Contingencies Disclosure [Line Items]
Outsourcing agreements, remaining term		2 years	2 years
Outsourcing agreements, aggregate remaining cost		$ 26	¥ 3
Information technology and data services company application maintenance and development services second agreement
Commitments and Contingencies Disclosure [Line Items]
Outsourcing agreements, remaining term		5 years	5 years
Outsourcing agreements, aggregate remaining cost		$ 65	¥ 7.4

COMMITMENTS AND CONTINGENT L133

COMMITMENTS AND CONTINGENT LIABILITIES - Future Minimum Lease Payments due under Non-Cancelable Operating Leases (Detail) $ in Millions	Dec. 31, 2017USD ($)
Commitments and Contingencies Disclosure [Abstract]
2,018	$ 61
2,019	33
2,020	24
2,021	21
2,022	16
Thereafter	30
Total future minimum lease payments	$ 185

Unaudited Consolidated Quart134

Unaudited Consolidated Quarterly Financial Data (Detail) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Income Statements, [Line Items]
Net premium income	$ 4,580,000,000	$ 4,648,000,000	$ 4,665,000,000	$ 4,638,000,000	$ 4,778,000,000	$ 5,022,000,000	$ 4,823,000,000	$ 4,602,000,000	$ 18,531,000,000	$ 19,225,000,000	$ 17,570,000,000
Net investment income	812,000,000	811,000,000	802,000,000	794,000,000	813,000,000	842,000,000	822,000,000	801,000,000	3,220,000,000	3,278,000,000	3,135,000,000
Realized investment gains (losses)	15,000,000	30,000,000	(56,000,000)	(140,000,000)	344,000,000	(164,000,000)	(223,000,000)	30,000,000
Other income (loss)	17,000,000	17,000,000	17,000,000	17,000,000	20,000,000	16,000,000	15,000,000	18,000,000	67,000,000	70,000,000	61,000,000
Total revenues	5,424,000,000	5,506,000,000	5,428,000,000	5,309,000,000	5,955,000,000	5,716,000,000	5,437,000,000	5,451,000,000	21,667,000,000	22,559,000,000	20,872,000,000
Total benefits and expenses	4,425,000,000	4,431,000,000	4,383,000,000	4,411,000,000	4,802,000,000	4,753,000,000	4,603,000,000	4,334,000,000	17,649,000,000	18,492,000,000	17,010,000,000
Earnings before income taxes	999,000,000	1,075,000,000	1,045,000,000	898,000,000	1,153,000,000	963,000,000	834,000,000	1,117,000,000	4,018,000,000	4,067,000,000	3,862,000,000
Total income tax expense	(1,585,000,000)	359,000,000	332,000,000	306,000,000	402,000,000	334,000,000	286,000,000	386,000,000	$ (586,000,000)	$ 1,408,000,000	$ 1,329,000,000
Net earnings	$ 2,584,000,000	$ 716,000,000	$ 713,000,000	$ 592,000,000	$ 751,000,000	$ 629,000,000	$ 548,000,000	$ 731,000,000
Net earnings per basic share	$ 6.59	$ 1.81	$ 1.80	$ 1.48	$ 1.85	$ 1.54	$ 1.33	$ 1.75	$ 11.63	$ 6.46	$ 5.88
Net earnings per diluted share	$ 6.54	$ 1.80	$ 1.79	$ 1.47	$ 1.84	$ 1.53	$ 1.32	$ 1.74	$ 11.54	$ 6.42	$ 5.85
Parent Company
Condensed Income Statements, [Line Items]
Net investment income									$ 30,000,000	$ 18,000,000	$ 22,000,000
Total revenues									331,000,000	213,000,000	321,000,000
Earnings before income taxes									(46,000,000)	(277,000,000)	(231,000,000)
Total income tax expense									$ (23,000,000)	$ (102,000,000)	$ (80,000,000)

SUBSEQUENT EVENTS - Additional

SUBSEQUENT EVENTS - Additional Information (Detail) shares in Thousands	Feb. 13, 2018	Mar. 16, 2018shares	Dec. 31, 2017shares	Dec. 31, 2016shares	Dec. 31, 2015shares
Subsequent Event [Line Items]
Common Stock, Shares, Outstanding			390,455	405,810	424,380
Subsequent Event
Subsequent Event [Line Items]
Two-for-one Stock Split, Conversion Ratio	2
Common Stock as a Percentage of Two-for-one Stock Split Dividend	100.00%
Two-for-one Stock Split, Common Stock, Shares, Outstanding		781,000

SUBSEQUENT EVENTS - Pro Forma E

SUBSEQUENT EVENTS - Pro Forma Earnings Per Share (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Subsequent Events [Abstract]
Two-for-one Stock Split, Diluted Earnings Per Share Pro Forma	$ 5.77	$ 3.21	$ 2.93

Schedule II - Aflac Incorporate

Schedule II - Aflac Incorporated (Parent Only) - Condensed Statement of Earnings (Detail) - USD ($)		1 Months Ended	3 Months Ended								12 Months Ended
		Nov. 30, 2017	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Income Statements, [Line Items]
Net investment income			$ 812,000,000	$ 811,000,000	$ 802,000,000	$ 794,000,000	$ 813,000,000	$ 842,000,000	$ 822,000,000	$ 801,000,000	$ 3,220,000,000	$ 3,278,000,000	$ 3,135,000,000
Realized investment gains (losses)											(151,000,000)	(14,000,000)	106,000,000
Other income (loss)			17,000,000	17,000,000	17,000,000	17,000,000	20,000,000	16,000,000	15,000,000	18,000,000	67,000,000	70,000,000	61,000,000
Total revenues			5,424,000,000	5,506,000,000	5,428,000,000	5,309,000,000	5,955,000,000	5,716,000,000	5,437,000,000	5,451,000,000	21,667,000,000	22,559,000,000	20,872,000,000
Interest expense											240,000,000	268,000,000	289,000,000
Earnings before income taxes			999,000,000	1,075,000,000	1,045,000,000	898,000,000	1,153,000,000	963,000,000	834,000,000	1,117,000,000	4,018,000,000	4,067,000,000	3,862,000,000
Current tax expense (benefit)											631,000,000	884,000,000	1,288,000,000
Deferred tax expense (benefit)											(1,217,000,000)	524,000,000	41,000,000
Total income tax expense			$ (1,585,000,000)	$ 359,000,000	$ 332,000,000	$ 306,000,000	$ 402,000,000	$ 334,000,000	$ 286,000,000	$ 386,000,000	(586,000,000)	1,408,000,000	1,329,000,000
Net earnings											4,604,000,000	2,659,000,000	2,533,000,000
Parent Company
Condensed Income Statements, [Line Items]
Management and service fees from subsidiaries	[1]										297,000,000	265,000,000	260,000,000
Net investment income											30,000,000	18,000,000	22,000,000
Interest from subsidiaries	[1]										5,000,000	5,000,000	6,000,000
Realized investment gains (losses)											67,000,000	84,000,000	86,000,000
Change in fair value on the cross-currency interest rate swaps											(68,000,000)	(159,000,000)	(53,000,000)
Total revenues											331,000,000	213,000,000	321,000,000
Interest expense											197,000,000	213,000,000	231,000,000
Other operating expenses	[2]										180,000,000	277,000,000	321,000,000
Total operating expenses											377,000,000	490,000,000	552,000,000
Earnings before income taxes											(46,000,000)	(277,000,000)	(231,000,000)
Total income tax expense											(23,000,000)	(102,000,000)	(80,000,000)
Earnings before equity in earnings of subsidiaries											(23,000,000)	(175,000,000)	(151,000,000)
Equity in earnings of subsidiaries	[1],[3]										4,627,000,000	2,834,000,000	2,684,000,000
Net earnings											4,604,000,000	2,659,000,000	2,533,000,000
5.50% subordinated notes due September 2052
Condensed Income Statements, [Line Items]
Expense on extinguishment of debt		$ 13,000,000									$ 13,000,000
Senior Notes due 2039 and 2040
Condensed Income Statements, [Line Items]
Expense on extinguishment of debt												$ 137,000,000
8.50% senior notes due May 2019
Condensed Income Statements, [Line Items]
Expense on extinguishment of debt													$ 230,000,000
[1]	Eliminated in consolidation
[2]	Includes expense of $13 in 2017, $137 in 2016 and $230 in 2015 for the early extinguishment of debt
[3]	Eliminated in consolidation

Schedule II - Aflac Incorpor138

Schedule II - Aflac Incorporated (Parent Only) - Condensed Statements of Comprehensive Income (Loss) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Financial Statements, Captions [Line Items]
Net earnings		$ 4,604	$ 2,659	$ 2,533
Other comprehensive income (loss) before income taxes:
Unrealized foreign currency translation gains (losses) during period		286	283	360
Unrealized gains (losses) on investment securities during period		1,731	2,852	(2,534)
Pension liability adjustment during period		9	(45)	(20)
Total other comprehensive income (loss) before income taxes		2,029	3,040	(2,255)
Income tax expense (benefit) related to items of other comprehensive income (loss)		631	1,035	(901)
Other comprehensive income (loss), net of income taxes	[1]	1,398	2,005	(1,354)
Total comprehensive income (loss)		6,002	4,664	1,179
Parent Company
Condensed Financial Statements, Captions [Line Items]
Net earnings		4,604	2,659	2,533
Other comprehensive income (loss) before income taxes:
Unrealized foreign currency translation gains (losses) during period		286	283	360
Unrealized gains (losses) on investment securities during period		1,733	2,799	(2,595)
Unrealized gains (losses) on derivatives during period		1	3	0
Pension liability adjustment during period		9	(45)	(20)
Total other comprehensive income (loss) before income taxes		2,029	3,040	(2,255)
Income tax expense (benefit) related to items of other comprehensive income (loss)		631	1,035	(901)
Other comprehensive income (loss), net of income taxes		1,398	2,005	(1,354)
Total comprehensive income (loss)		$ 6,002	$ 4,664	$ 1,179
[1]	All amounts in the table above are net of tax.

Schedule II - Aflac Incorpor139

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

Schedule II - Aflac Incorpor140

Schedule II - Aflac Incorporated (Parent Only) - Condensed Balance Sheet (Detail 2) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Financial Statements, Captions [Line Items]
Common stock, par value (in dollars per share)	$ 0.10	$ 0.10
Common stock, shares authorized (in shares)	1,900,000	1,900,000
Common stock, shares issued (in shares)	672,881	671,249	669,723	668,132
Parent Company
Condensed Financial Statements, Captions [Line Items]
Securities available for sale, fixed maturities, amortized cost	$ 1,163	$ 483
Common stock, par value (in dollars per share)	$ 0.10	$ 0.10
Common stock, shares authorized (in shares)	1,900,000	1,900,000
Common stock, shares issued (in shares)	672,881	671,249

Schedule II - Aflac Incorpor141

Schedule II - Aflac Incorporated (Parent Only) - Condensed Statements of Cash Flows (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016		Dec. 31, 2015
Cash flows from operating activities:
Net earnings		$ 4,604	$ 2,659		$ 2,533
Adjustments to reconcile net earnings to net cash provided from operating activities:
Other, net		150	340	[1]	955	[1]
Net cash provided (used) by operating activities		6,128	5,987		6,776
Cash flows from investing activities:
Fixed maturity securities sold		3,819	5,157		3,224
Fixed maturity securities purchased		(9,867)	(10,890)		(6,507)
Other investments sold (purchased)		(2,018)	(1,118)		(70)
Settlement of derivatives		(621)	1,252		(2,119)
Payments for (Proceeds from) Other Investing Activities		(68)	(76)		(86)
Net cash provided (used) by investing activities		(5,431)	(3,855)		(4,897)
Cash flows from financing activities:
Purchases of treasury stock		(1,351)	(1,422)		(1,315)
Proceeds from borrowings		1,040	986		998
Principal payments under debt obligations		(1,161)	(610)		(1,272)
Dividends paid to shareholders		(661)	(658)		(656)
Treasury stock reissued		33	46		36
Proceeds from exercise of stock options		58	68		68
Other, net		0	(120)	[1]	(234)	[1]
Net cash provided (used) by financing activities		(2,065)	(1,619)		(2,187)
Net change in cash and cash equivalents		(1,368)	509		(308)
Cash and cash equivalents, beginning of period		4,859	4,350		4,658
Cash and cash equivalents, end of period		3,491	4,859		4,350
Parent Company
Cash flows from operating activities:
Net earnings		4,604	2,659		2,533
Adjustments to reconcile net earnings to net cash provided from operating activities:
Equity in earnings of subsidiaries	[2],[3]	(4,627)	(2,834)		(2,684)
Cash dividends received from subsidiaries		2,001	2,020		2,393
Other, net		(46)	294	[4]	155	[4]
Net cash provided (used) by operating activities		1,932	2,139		2,397
Cash flows from investing activities:
Fixed maturity securities sold		263	225		121
Fixed maturity securities purchased		(329)	(229)		(202)
Other investments sold (purchased)		(47)	6		14
Settlement of derivatives		223	0		147
Additional capitalization of subsidiaries	[3]	(69)	(36)		(43)
Payments for (Proceeds from) Other Investing Activities		(218)	(25)		0
Net cash provided (used) by investing activities		(177)	(59)		37
Cash flows from financing activities:
Purchases of treasury stock		(1,351)	(1,422)		(1,315)
Proceeds from borrowings		1,040	986		998
Principal payments under debt obligations		(1,161)	(621)		(1,272)
Dividends paid to shareholders		(661)	(658)		(656)
Treasury stock reissued		33	46		36
Proceeds from exercise of stock options		38	36		47
Net change in amount due to/from subsidiary	[3]	(5)	(6)		43
Other, net		0	(125)	[4]	(232)	[4]
Net cash provided (used) by financing activities		(2,067)	(1,764)		(2,351)
Net change in cash and cash equivalents		(312)	316		83
Cash and cash equivalents, beginning of period		2,037	1,721		1,638
Cash and cash equivalents, end of period		$ 1,725	2,037		1,721
Senior Notes due 2039 and 2040
Condensed Cash Flow Statements, Captions [Line Items]
Expense on extinguishment of debt			$ 137
8.50% senior notes due May 2019
Condensed Cash Flow Statements, Captions [Line Items]
Expense on extinguishment of debt					$ 230
[1]	Operating activities excludes and financing activities includes a cash outflow of $137 in 2016 and $230 in 2015 for the payments associated with the early extinguishment of debt
[2]	Eliminated in consolidation
[3]	Eliminated in consolidation
[4]	Operating activities excludes and financing activities includes a cash outflow of $137 in 2016 and $230 in 2015 for the payments associated with the early extinguishment of debt

Schedule II - Aflac Incorpor142

Schedule II - Aflac Incorporated (Parent Only) - Summary of Notes Payable (Detail 1) - USD ($) $ in Millions	Dec. 31, 2017		Dec. 31, 2016
Condensed Financial Statements, Captions [Line Items]
Notes payable	$ 5,267		$ 5,339
Parent Company
Condensed Financial Statements, Captions [Line Items]
Notes payable	5,267		5,339
Parent Company | 2.65% senior notes paid February 2017
Condensed Financial Statements, Captions [Line Items]
Notes payable	0		649
Parent Company | 2.40% senior notes due March 2020
Condensed Financial Statements, Captions [Line Items]
Notes payable	548		547
Parent Company | 4.00% senior notes due February 2022
Condensed Financial Statements, Captions [Line Items]
Notes payable	348		348
Parent Company | 3.625% senior notes due June 2023
Condensed Financial Statements, Captions [Line Items]
Notes payable	697		696
Parent Company | 3.625% senior notes due November 2024
Condensed Financial Statements, Captions [Line Items]
Notes payable	745		745
Parent Company | 3.25% senior notes due March 2025
Condensed Financial Statements, Captions [Line Items]
Notes payable	446		445
Parent Company | 2.875% senior notes due October 2026
Condensed Financial Statements, Captions [Line Items]
Notes payable	297		298
Parent Company | 6.90% senior notes due December 2039
Condensed Financial Statements, Captions [Line Items]
Notes payable	220		220
Parent Company | 6.45% senior notes due August 2040
Condensed Financial Statements, Captions [Line Items]
Notes payable	254		254
Parent Company | 4.00% senior notes due October 2046
Condensed Financial Statements, Captions [Line Items]
Notes payable	394		394
Parent Company | 5.50% subordinated notes due September 2052
Condensed Financial Statements, Captions [Line Items]
Notes payable	0	[1]	486
Parent Company | .932% senior notes due January 2027
Condensed Financial Statements, Captions [Line Items]
Notes payable	528		0
Parent Company | 2.108% subordinated notes due October 2047
Condensed Financial Statements, Captions [Line Items]
Notes payable	526		0
Parent Company | Yen-denominated loan variable interest rate due September 2021
Condensed Financial Statements, Captions [Line Items]
Notes payable	44		43
Parent Company | Yen-denominated loan variable interest rate due September 2023
Condensed Financial Statements, Captions [Line Items]
Notes payable	$ 220		$ 214
[1]	Redeemed in November 2017

Schedule II - Aflac Incorpor143

Schedule II - Aflac Incorporated (Parent Only) - Summary of Notes Payable (Detail 2) $ in Millions, ¥ in Billions	Dec. 31, 2017USD ($)		Dec. 31, 2017JPY (¥)	Nov. 30, 2017	Oct. 31, 2017JPY (¥)	Feb. 28, 2017	Jan. 31, 2017JPY (¥)	Dec. 31, 2016USD ($)	Dec. 31, 2016JPY (¥)	Sep. 30, 2016USD ($)	Sep. 30, 2016JPY (¥)	Mar. 31, 2015USD ($)	Nov. 30, 2014USD ($)	Jun. 30, 2013USD ($)	Oct. 31, 2012USD ($)	Sep. 30, 2012USD ($)	Jul. 31, 2012USD ($)	Feb. 29, 2012USD ($)	Aug. 31, 2010USD ($)	Dec. 31, 2009USD ($)
Condensed Financial Statements, Captions [Line Items]
Notes payable	$ 5,267							$ 5,339
2.65% senior notes paid February 2017
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate						2.65%		2.65%	2.65%								2.65%	2.65%
Debt instrument, principal amount																	$ 250	$ 400
2.40% senior notes due March 2020
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	2.40%		2.40%					2.40%	2.40%			2.40%
Debt instrument, principal amount	$ 550											$ 550
4.00% senior notes due February 2022
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	4.00%		4.00%					4.00%	4.00%									4.00%
Debt instrument, principal amount	$ 350																	$ 350
3.625% senior notes due June 2023
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	3.625%		3.625%					3.625%	3.625%					3.625%
Debt instrument, principal amount	$ 700													$ 700
3.625% senior notes due November 2024
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	3.625%		3.625%					3.625%	3.625%				3.625%
Debt instrument, principal amount	$ 750												$ 750
3.25% senior notes due March 2025
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	3.25%		3.25%					3.25%	3.25%			3.25%
Debt instrument, principal amount	$ 450											$ 450
2.875% senior notes due October 2026
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	2.875%		2.875%					2.875%	2.875%	2.875%	2.875%
Debt instrument, principal amount										$ 300
6.90% senior notes due December 2039
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	6.90%		6.90%					6.90%	6.90%
Debt instrument, principal amount																				$ 400
6.45% senior notes due August 2040
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	6.45%		6.45%					6.45%	6.45%
Debt instrument, principal amount																			$ 450
4.00% senior notes due October 2046
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	4.00%		4.00%					4.00%	4.00%	4.00%	4.00%
Debt instrument, principal amount										$ 400
5.50% subordinated notes due September 2052
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate				5.50%				5.50%	5.50%						5.50%	5.50%
Debt instrument, principal amount															$ 50	$ 450
.932% senior notes due January 2027
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	0.932%		0.932%				0.932%
Debt instrument, principal amount | ¥			¥ 60				¥ 60
2.108% subordinated notes due October 2047
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	2.108%		2.108%		2.108%
Debt instrument, principal amount | ¥			¥ 60		¥ 60
Yen-denominated loan variable interest rate due September 2021
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	0.32%		0.32%					0.31%	0.31%
Debt instrument, principal amount | ¥			¥ 5						¥ 5		¥ 5
Yen-denominated loan variable interest rate due September 2023
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	0.47%		0.47%					0.46%	0.46%
Debt instrument, principal amount | ¥			¥ 25						¥ 25		¥ 25
Parent Company
Condensed Financial Statements, Captions [Line Items]
Notes payable	$ 5,267							$ 5,339
Parent Company | 2.65% senior notes paid February 2017
Condensed Financial Statements, Captions [Line Items]
Notes payable	0							$ 649
Debt instrument, interest rate						2.65%		2.65%	2.65%
Parent Company | 2.40% senior notes due March 2020
Condensed Financial Statements, Captions [Line Items]
Notes payable	$ 548							$ 547
Debt instrument, interest rate	2.40%		2.40%					2.40%	2.40%
Parent Company | 4.00% senior notes due February 2022
Condensed Financial Statements, Captions [Line Items]
Notes payable	$ 348							$ 348
Debt instrument, interest rate	4.00%		4.00%					4.00%	4.00%
Parent Company | 3.625% senior notes due June 2023
Condensed Financial Statements, Captions [Line Items]
Notes payable	$ 697							$ 696
Debt instrument, interest rate	3.625%		3.625%					3.625%	3.625%
Parent Company | 3.625% senior notes due November 2024
Condensed Financial Statements, Captions [Line Items]
Notes payable	$ 745							$ 745
Debt instrument, interest rate	3.625%		3.625%					3.625%	3.625%
Parent Company | 3.25% senior notes due March 2025
Condensed Financial Statements, Captions [Line Items]
Notes payable	$ 446							$ 445
Debt instrument, interest rate	3.25%		3.25%					3.25%	3.25%
Parent Company | 2.875% senior notes due October 2026
Condensed Financial Statements, Captions [Line Items]
Notes payable	$ 297							$ 298
Debt instrument, interest rate	2.875%		2.875%					2.875%	2.875%
Parent Company | 6.90% senior notes due December 2039
Condensed Financial Statements, Captions [Line Items]
Notes payable	$ 220							$ 220
Debt instrument, interest rate	6.90%		6.90%					6.90%	6.90%
Parent Company | 6.45% senior notes due August 2040
Condensed Financial Statements, Captions [Line Items]
Notes payable	$ 254							$ 254
Debt instrument, interest rate	6.45%		6.45%					6.45%	6.45%
Parent Company | 4.00% senior notes due October 2046
Condensed Financial Statements, Captions [Line Items]
Notes payable	$ 394							$ 394
Debt instrument, interest rate	4.00%		4.00%					4.00%	4.00%
Parent Company | 5.50% subordinated notes due September 2052
Condensed Financial Statements, Captions [Line Items]
Notes payable	$ 0	[1]						$ 486
Debt instrument, interest rate				5.50%				5.50%	5.50%
Parent Company | .932% senior notes due January 2027
Condensed Financial Statements, Captions [Line Items]
Notes payable	$ 528							$ 0
Debt instrument, interest rate	0.932%		0.932%				0.932%
Debt instrument, principal amount | ¥			¥ 60				¥ 60
Parent Company | 2.108% subordinated notes due October 2047
Condensed Financial Statements, Captions [Line Items]
Notes payable	$ 526							0
Debt instrument, interest rate	2.108%		2.108%		2.108%
Debt instrument, principal amount | ¥			¥ 60		¥ 60
Parent Company | Yen-denominated loan variable interest rate due September 2021
Condensed Financial Statements, Captions [Line Items]
Notes payable	$ 44							$ 43
Debt instrument, interest rate	0.32%		0.32%					0.31%	0.31%
Debt instrument, principal amount | ¥			¥ 5						¥ 5
Parent Company | Yen-denominated loan variable interest rate due September 2023
Condensed Financial Statements, Captions [Line Items]
Notes payable	$ 220							$ 214
Debt instrument, interest rate	0.47%		0.47%					0.46%	0.46%
Debt instrument, principal amount | ¥			¥ 25						¥ 25
[1]	Redeemed in November 2017

Schedule II - Aflac Incorpor144

Schedule II - Aflac Incorporated (Parent Only) - Additional Information (Detail) $ in Millions, ¥ in Billions	1 Months Ended
	Nov. 30, 2017USD ($)	Oct. 31, 2017JPY (¥)	Feb. 28, 2017USD ($)	Jan. 31, 2017JPY (¥)	Sep. 30, 2012USD ($)	Jul. 31, 2012USD ($)	Feb. 29, 2012USD ($)	Dec. 31, 2017JPY (¥)	Dec. 31, 2016	Oct. 31, 2012USD ($)
2.108% subordinated notes due October 2047
Condensed Financial Statements, Captions [Line Items]
Debt Instrument, Face Amount | ¥		¥ 60						¥ 60
Debt Instrument, Interest Rate, Stated Percentage		2.108%						2.108%
Debt instrument, term		30 years
Debt Instrument, Redemption, Description		The debentures are redeemable (i) at any time, in whole but not in part, upon the occurrence of certain tax events or certain rating agency events, as specified in the indenture governing the terms of the debentures or (ii) on or after October 23, 2027, in whole or in part, at a redemption price equal to their principal amount plus accrued and unpaid interest to, but excluding, the date of redemption.
Debt Instrument, Call Date, Earliest		Oct. 23, 2027
Debt Instrument, Interest Rate Terms		The debentures bear interest at an initial rate of 2.108% per annum through October 22, 2027, or earlier redemption. Thereafter, the rate of the interest of the debentures will be reset every five years at a rate of interest equal to the then-current JPY 5-year Swap Offered Rate plus 205 basis points.
.932% senior notes due January 2027
Condensed Financial Statements, Captions [Line Items]
Debt Instrument, Face Amount | ¥				¥ 60				¥ 60
Debt Instrument, Interest Rate, Stated Percentage				0.932%				0.932%
Debt instrument, term				10 years
2.65% senior notes paid February 2017
Condensed Financial Statements, Captions [Line Items]
Debt Instrument, Face Amount						$ 250	$ 400
Debt Instrument, Interest Rate, Stated Percentage			2.65%			2.65%	2.65%		2.65%
Debt instrument, term						5 years	5 years
Repayments of debt			$ 650
5.50% subordinated notes due September 2052
Condensed Financial Statements, Captions [Line Items]
Debt Instrument, Face Amount					$ 450					$ 50
Debt Instrument, Interest Rate, Stated Percentage	5.50%				5.50%				5.50%	5.50%
Debt instrument, term					40 years
Repayments of debt	$ 500
Parent Company | 2.108% subordinated notes due October 2047
Condensed Financial Statements, Captions [Line Items]
Debt Instrument, Face Amount | ¥		¥ 60						¥ 60
Debt Instrument, Interest Rate, Stated Percentage		2.108%						2.108%
Debt instrument, term		30 years
Debt Instrument, Redemption, Description		The debentures are redeemable (i) at any time, in whole but not in part, upon the occurrence of certain tax events or certain rating agency events, as specified in the indenture governing the terms of the debentures or (ii) on or after October 23, 2027, in whole or in part, at a redemption price equal to their principal amount plus accrued and unpaid interest to, but excluding, the date of redemption.
Debt Instrument, Call Date, Earliest		Oct. 23, 2027
Debt Instrument, Interest Rate Terms		The debentures bear interest at an initial rate of 2.108% per annum through October 22, 2027, or earlier redemption. Thereafter, the rate of the interest of the debentures will be reset every five years at a rate of interest equal to the then-current JPY 5-year Swap Offered Rate plus 205 basis points.
Parent Company | .932% senior notes due January 2027
Condensed Financial Statements, Captions [Line Items]
Debt Instrument, Face Amount | ¥				¥ 60				¥ 60
Debt Instrument, Interest Rate, Stated Percentage				0.932%				0.932%
Debt instrument, term				10 years
Parent Company | 2.65% senior notes paid February 2017
Condensed Financial Statements, Captions [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			2.65%						2.65%
Repayments of debt			$ 650
Parent Company | 5.50% subordinated notes due September 2052
Condensed Financial Statements, Captions [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.50%								5.50%
Repayments of debt	$ 500

Schedule II - Aflac Incorpor145

Schedule II - Aflac Incorporated - Aggregate Contractual Maturities of Notes Payable (Detail) $ in Millions	Dec. 31, 2017USD ($)
Condensed Financial Statements, Captions [Line Items]
2,018	$ 8
2,019	7
2,020	553
2,021	46
2,022	351
Thereafter	4,365
Total	5,330
Parent Company
Condensed Financial Statements, Captions [Line Items]
2,018	0
2,019	0
2,020	550
2,021	44
2,022	350
Thereafter	4,364
Total	$ 5,308

Schedule II - Aflac Incorpor146

Schedule II - Aflac Incorporated (Parent Only) - Supplemental Disclosure of Cash Flow Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Cash Flow Statements, Captions [Line Items]
Interest paid	$ 196	$ 211	$ 236
Shareholder dividend reinvestment
Condensed Cash Flow Statements, Captions [Line Items]
Treasury stock issued for shareholder dividend reinvestment	29	27	26
Parent Company
Condensed Cash Flow Statements, Captions [Line Items]
Interest paid	195	209	235
Parent Company | Shareholder dividend reinvestment
Condensed Cash Flow Statements, Captions [Line Items]
Treasury stock issued for shareholder dividend reinvestment	$ 29	$ 26	$ 26

SCHEDULE III SUPPLEMENTARY I147

SCHEDULE III SUPPLEMENTARY INSURANCE INFORMATION - (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplementary Insurance Information, by Segment [Line Items]
Deferred policy acquisition costs	$ 9,505				$ 8,993				$ 9,505	$ 8,993
Future policy benefits & unpaid policy claims	86,249				80,151				86,249	80,151
Unearned premiums	5,959				6,916				5,959	6,916
Other policyholders' funds	6,939				6,659				6,939	6,659
Premiums Earned, Net	4,580	$ 4,648	$ 4,665	$ 4,638	4,778	$ 5,022	$ 4,823	$ 4,602	18,531	19,225	$ 17,570
Net investment income	812	$ 811	$ 802	$ 794	813	$ 842	$ 822	$ 801	3,220	3,278	3,135
Benefits and claims, net									12,181	12,919	11,746
Amortization of deferred policy acquisition costs									1,132	1,141	1,066
Other operating expenses									4,336	4,432	4,198
Premiums written									17,657	18,214	17,083
Aflac Japan
Supplementary Insurance Information, by Segment [Line Items]
Deferred policy acquisition costs	6,150				5,765				6,150	5,765	5,370
Future policy benefits & unpaid policy claims	76,353				70,684				76,353	70,684
Unearned premiums	5,840				6,798				5,840	6,798
Other policyholders' funds	6,939				6,659				6,939	6,659
Premiums Earned, Net									12,752	13,537	12,046
Net investment income									2,463	2,554	2,436
Benefits and claims, net									9,087	9,828	8,705
Amortization of deferred policy acquisition costs									630	644	578
Other operating expenses									2,257	2,326	2,055
Premiums written									12,092	12,762	11,740
Aflac U.S.
Supplementary Insurance Information, by Segment [Line Items]
Deferred policy acquisition costs	3,355				3,228				3,355	3,228	3,141
Future policy benefits & unpaid policy claims	10,506				10,094				10,506	10,094
Unearned premiums	119				118				119	118
Other policyholders' funds	0				0				0	0
Premiums Earned, Net									5,563	5,454	5,347
Net investment income									721	703	678
Benefits and claims, net									2,885	2,869	2,873
Amortization of deferred policy acquisition costs									502	497	488
Other operating expenses									1,658	1,593	1,570
Premiums written									5,565	5,452	5,343
All other
Supplementary Insurance Information, by Segment [Line Items]
Deferred policy acquisition costs	0				0				0	0
Future policy benefits & unpaid policy claims	138				91				138	91
Unearned premiums	0				0				0	0
Other policyholders' funds	0				0				0	0
Premiums Earned, Net									216	234	177
Net investment income									36	21	21
Benefits and claims, net									209	222	168
Amortization of deferred policy acquisition costs									0	0	0
Other operating expenses									421	513	573
Premiums written									0	0	$ 0
Intercompany eliminations
Supplementary Insurance Information, by Segment [Line Items]
Deferred policy acquisition costs	0				0				0	0
Future policy benefits & unpaid policy claims	(748)				(718)				(748)	(718)
Unearned premiums	0				0				0	0
Other policyholders' funds	$ 0				$ 0				$ 0	$ 0

SCHEDULE IV REINSURANCE Schedul

SCHEDULE IV REINSURANCE Schedule IV - Reinsurance (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Gross Amount, Life Insurance in Force	$ 152,502				$ 151,093				$ 152,502	$ 151,093	$ 146,610
Ceded to Other Companies, Life Insurance in Force	4,121				3,741				4,121	3,741	3,547
Assumed from Other Companies, Life Insurance in Force	0				0				0	0	0
Net Amount, Life Insurance in Force	$ 148,381				$ 147,352				$ 148,381	$ 147,352	$ 143,063
Percentage of Amount Assumed to Net, Life Insurance in Force	0.00%				0.00%				0.00%	0.00%	0.00%
Gross amount									$ 18,875	$ 19,592	$ 17,904
Ceded to Other Companies									566	608	520
Assumed from Other companies									222	241	186
Net Amount	$ 4,580	$ 4,648	$ 4,665	$ 4,638	$ 4,778	$ 5,022	$ 4,823	$ 4,602	$ 18,531	$ 19,225	$ 17,570
Percentage of Amount Assumed to Net									1.00%	1.00%	1.00%
Health insurance
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Gross amount									$ 14,829	$ 14,839	$ 13,604
Ceded to Other Companies									554	595	509
Assumed from Other companies									222	241	186
Net Amount									$ 14,497	$ 14,485	$ 13,281
Percentage of Amount Assumed to Net									1.00%	1.00%	1.00%
Life insurance
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Gross amount									$ 4,046	$ 4,753	$ 4,300
Ceded to Other Companies									12	13	11
Assumed from Other companies									0	0	0
Net Amount									$ 4,034	$ 4,740	$ 4,289
Percentage of Amount Assumed to Net									0.00%	0.00%	0.00%