Debt default minimum.

No definition available.

Name:	ahl_DebtDefaultMinimum
Namespace Prefix:	ahl_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Line of credit facility Increasable capacity.

+ References

No definition available.

+ Details

Name:	ahl_LineOfCreditFacilityIncreasableCapacity
Namespace Prefix:	ahl_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Line of credit facility increase additional borrowing capacity.

+ References

No definition available.

+ Details

Name:	ahl_LineOfCreditFacilityIncreaseAdditionalBorrowingCapacity
Namespace Prefix:	ahl_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Line of credit facility tangible net worth cash proceeds from the issuance of capital stock restriction.

+ References

No definition available.

+ Details

Name:	ahl_LineOfCreditFacilityTangibleNetWorthCashProceedsFromIssuanceOfCapitalStockRestriction
Namespace Prefix:	ahl_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Line of credit facility tangible net worth net income restriction.

+ References

No definition available.

+ Details

Name:	ahl_LineOfCreditFacilityTangibleNetWorthNetIncomeRestriction
Namespace Prefix:	ahl_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Line of credit facility tangible net worth restrictions minimum.

+ References

No definition available.

+ Details

Name:	ahl_LineOfCreditFacilityTangibleNetWorthRestrictionsMinimum
Namespace Prefix:	ahl_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Payment for Extinguishment of Debt

+ References

No definition available.

+ Details

Name:	ahl_PaymentforExtinguishmentofDebt
Namespace Prefix:	ahl_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Percentage of consolidated leverage ratio permitted.

+ References

No definition available.

+ Details

Name:	ahl_PercentageOfConsolidatedLeverageRatioPermitted
Namespace Prefix:	ahl_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

+ Details

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910

+ Details

Name:	us-gaap_LineOfCredit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The effective interest rate during the reporting period.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityInterestRateDuringPeriod
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_LineOfCreditFacilityLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of the required periodic payment applied to interest.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityPeriodicPaymentInterest
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The fair value of notes issued in noncash investing and financing activities.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 4
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-Topic 230
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4304-108586

+ Details

Name:	us-gaap_NotesIssued1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The cash inflow from a borrowing with the highest claim on the assets of the entity in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle, if longer).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3255-108585

+ Details

Name:	us-gaap_ProceedsFromIssuanceOfSeniorLongTermDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_CreditFacilityAxis=ahl_CitibankEuropeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LineOfCreditFacilityAxis=ahl_CitibankEuropeplcMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_LetterOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LineOfCreditFacilityAxis=us-gaap_SeniorNotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LineOfCreditFacilityAxis=ahl_Silverton2015Member
Namespace Prefix:
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Balance Type:
Period Type:

- Details

Name:	us-gaap_LineOfCreditFacilityAxis=ahl_Silverton2015ThirdpartyFundedMember
Namespace Prefix:
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Balance Type:
Period Type:

- Details

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- Details

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Credit Facility and Long-Term Debt - Additional Information (Details) - USD ($)				3 Months Ended			12 Months Ended
	Mar. 27, 2017	Nov. 13, 2013	Dec. 15, 2010	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2014	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jun. 30, 2016
Line of Credit Facility [Line Items]
Revolving credit facility, credit agreement maximum limit	$ 200,000,000
Line of credit facility Increasable capacity	$ 100,000,000
Line of credit facility borrowings outstanding							$ 0
Minimum consolidated tangible net worth under credit facility							$ 2,323,100,000.0
Percentage of consolidated net income							25.00%
Percentage of aggregate net cash proceeds from the issuance of capital stock							25.00%
Percentage of consolidated leverage ratio permitted							35.00%
Payment for extinguishment of debt							$ 5,500,000	$ 8,600,000	$ 0
Citibank Europe
Line of Credit Facility [Line Items]
Outstanding collateralized letters of credit facility							$ 444,200,000	444,200,000
London Interbank Offered Rate (LIBOR)
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate During Period							1.00%
Citibank Europe plc \| Letters of credit / guarantees
Line of Credit Facility [Line Items]
Revolving credit facility, credit agreement maximum limit										$ 500,000,000.0
Senior Notes
Line of Credit Facility [Line Items]
Debt stated interest rate		4.65%	6.00%
Net proceeds from senior notes		$ 299,700,000	$ 247,500,000
Loans issued		$ 300,000,000.0	$ 250,000,000.0
Amount of indebtedness subject to default in payment							$ 50,000,000.0
Annual interest payable							$ 14,000,000
Silverton 2015
Line of Credit Facility [Line Items]
Loan notes issued by third parties						$ 85,000,000
Silverton 2015, Third-party Funded
Line of Credit Facility [Line Items]
Loan notes issued by third parties						$ 70,000,000
Silverton 2016
Line of Credit Facility [Line Items]
Loan notes issued by third parties					$ 125,000,000
Silverton 2017
Line of Credit Facility [Line Items]
Loan notes issued by third parties				$ 130,000,000
Silverton 2017, Third-party Funded
Line of Credit Facility [Line Items]
Loan notes issued by third parties								$ 105,000,000
Silverton 2016, Third-party Funded
Line of Credit Facility [Line Items]
Loan notes issued by third parties					$ 100,000,000