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INVESTMENTS - Economic Maturities of Investments in Perpetual Securities (Detail) $ in Millions | Sep. 30, 2017 USD ($)
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Aflac Japan |
Investments Classified by Economic Maturity Date [Line Items] |
Due in one year or less | $ 84
Due after one year through five years | 194
Due after 10 years | 1,232
Total perpetual securities available for sale, amortized cost | 1,510
Due in one year or less | 85
Due after one year through five years | 236
Due after 10 years | 1,482
Total perpetual securities available for sale, fair value | 1,803
Aflac U.S. |
Investments Classified by Economic Maturity Date [Line Items] |
Due in one year or less | 0
Due after one year through five years | 0
Due after 10 years | 39
Total perpetual securities available for sale, amortized cost | 39
Due in one year or less | 0
Due after one year through five years | 0
Due after 10 years | 60
Total perpetual securities available for sale, fair value | $ 60

X
- Definition This item represents perpetual securities, at cost, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments, as defined), and fair value hedge accounting adjustments, if any, which are expected to mature after one year and through five years from the balance sheet date and which are categorized neither as held-to-maturity nor trading securities. + References No definition available. + Details
Name: | afl_AvailableForSaleSecuritiesPerpetualSecuritiesEconomicMaturitiesAfterOneThroughFiveYearsAmortizedCost
Namespace Prefix: | afl_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the fair value of perpetual securities which are expected to mature after one year and through five years from the balance sheet date and which are categorized neither as held-to-maturity nor trading securities. + References No definition available. + Details
Name: | afl_AvailableForSaleSecuritiesPerpetualSecuritiesEconomicMaturitiesAfterOneThroughFiveYearsFairValue
Namespace Prefix: | afl_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents perpetual securities, at cost, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments, as defined), and fair value hedge accounting adjustments, if any, which are expected to mature after ten years from the balance sheet date and which are categorized neither as held-to-maturity nor trading securities. + References No definition available. + Details
Name: | afl_AvailableForSaleSecuritiesPerpetualSecuritiesEconomicMaturitiesAfterTenYearsAmortizedCost
Namespace Prefix: | afl_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Available for sale Securities, Perpetual Securities, Economic Maturities, after Ten Years, Fair Value + References No definition available. + Details
Name: | afl_AvailableForSaleSecuritiesPerpetualSecuritiesEconomicMaturitiesAfterTenYearsFairValue
Namespace Prefix: | afl_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the total of all perpetual securities grouped by economic maturity dates, at cost, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments, as defined), and fair value hedge accounting adjustments, if any, which are categorized neither as held-to-maturity nor trading securities. + References No definition available. + Details
Name: | afl_AvailableForSaleSecuritiesPerpetualSecuritiesEconomicMaturitiesAmortizedCost
Namespace Prefix: | afl_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the total of all perpetual securities grouped by economic maturity dates, at fair value, which are categorized neither as held-to-maturity nor trading securities. + References No definition available. + Details
Name: | afl_AvailableForSaleSecuritiesPerpetualSecuritiesEconomicMaturitiesFairValue
Namespace Prefix: | afl_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents perpetual securities, at cost, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments, as defined), and fair value hedge accounting adjustments, if any, which are expected to mature within one year of the balance sheet date and which are categorized neither as held-to-maturity nor trading securities. + References No definition available. + Details
Name: | afl_AvailableForSaleSecuritiesPerpetualSecuritiesEconomicMaturitiesWithinOneYearAmortizedCost
Namespace Prefix: | afl_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the fair value of perpetual securities which are expected to mature within one year of the balance sheet date and which are categorized neither as held-to-maturity nor trading securities. + References No definition available. + Details
Name: | afl_AvailableForSaleSecuritiesPerpetualSecuritiesEconomicMaturitiesWithinOneYearFairValue
Namespace Prefix: | afl_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Investments Classified by Economic Maturity Date [Line Items] + References No definition available. + Details
Name: | afl_InvestmentsClassifiedByEconomicMaturityDateLineItems
Namespace Prefix: | afl_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=afl_AflacJapanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=afl_AflacUsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |