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Reinsurance - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Reinsurance Disclosures [Abstract]
Liability for unpaid claims and claims adjustment expense amount ceded	$ 125.5	$ (85.8)

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- Definition

Liability For Unpaid Claims And Claims Adjustment Expense Amount Disposed of or Ceded

+ References

No definition available.

+ Details

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

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- References

No definition available.

+ Details

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