Line of credit facility Increasable capacity.

No definition available.

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

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

Restricted assets.

+ References

No definition available.

+ Details

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

- Definition

Carrying amount of cash and investment securities on deposit with state regulatory authorities in connection with capital requirements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 320
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=75027294&loc=d3e22002-158495

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

Name:	us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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://www.xbrl.org/2003/role/presentationRef
-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

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-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=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-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

+ Details

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

- 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 minimum net capital required to be maintained to engage in securities transactions.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Rule 15c3-1
-Number 240
-Section 15c3-1

+ Details

Name:	us-gaap_MinimumNetCapitalRequired1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

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

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_RealEstateFundsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Commitments and Contingent Liabilities - Narrative (Details) £ in Millions			3 Months Ended
	Mar. 27, 2017 USD ($)	Jun. 30, 2016	Mar. 31, 2018 USD ($)	Mar. 31, 2018 GBP (£)	Dec. 31, 2017 USD ($)	Dec. 31, 2017 GBP (£)	Mar. 31, 2017 USD ($)
Line of Credit Facility [Line Items]
Restricted assets			$ 4,574,900,000		$ 4,638,800,000
Assets held by insurance regulators			452,800,000		458,700,000
Minimum capital required \| £				£ 0.4		£ 0.4
Maximum borrowing capacity	$ 200,000,000
Line Of Credit Facility Increasable Capacity	$ 100,000,000
Long-term Line of Credit			0
Line Of Credit Facility Tangible Net Worth Restrictions Minimum			$ 2,323,100,000
Line Of Credit Facility Tangible Net Worth Net Income Restriction			25.00%
Line Of Credit Facility Tangible Net Worth Cash Proceeds From Issuance Of Capital Stock Restriction			25.00%
Percentage Of Consolidated Leverage Ratio Permitted			35.00%
Letter of Credit
Line of Credit Facility [Line Items]
Restricted assets			$ 792,700,000		658,500,000
Citi Europe \| Letter of Credit
Line of Credit Facility [Line Items]
Maximum borrowing capacity							$ 550,000,000
Outstanding letters of credit			444,200,000		449,400,000
LIBOR \| Citi Europe \| Letter of Credit
Line of Credit Facility [Line Items]
Variable rate basis spread		1.00%
Real estate funds
Line of Credit Facility [Line Items]
Restricted assets			$ 100,000,000		$ 100,000,000