XML 79 R63.htm IDEA: XBRL DOCUMENT v3.21.1

Investments - Cost, Gross Unrealized Gains and Losses, and Estimated Fair Value of Available for Sale Investments in Fixed Income Maturities and Short-Term Investments (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Schedule of Trading Securities and Other Trading Items [Line Items]
Short term investment, available for sale(amortized cost - $117.6 and $117.66)	$ 4,348.1	$ 4,958.2
Gross unrealized gains	222.4	116.8
Gross unrealized losses	(0.8)	(3.8)
Allowance for credit loss	(0.2)
Total, Available for sale investments in fixed income maturities, Cost or Amortized Cost	4,126.7	4,845.2
Total short-term investments — Available for sale
Schedule of Trading Securities and Other Trading Items [Line Items]
Short term investment, available for sale(amortized cost - $117.6 and $117.66)	87.8	117.6
Gross unrealized gains	0.0	0.0
Gross unrealized losses	(0.2)	0.0
Allowance for credit loss	0.0
Total, Available for sale investments in fixed income maturities, Cost or Amortized Cost	88.0	117.6
Total fixed income securities — Available for sale
Schedule of Trading Securities and Other Trading Items [Line Items]
Short term investment, available for sale(amortized cost - $117.6 and $117.66)	4,435.9	5,075.8
Gross unrealized gains	222.4	116.8
Gross unrealized losses	(1.0)	(3.8)
Allowance for credit loss	(0.2)
Total, Available for sale investments in fixed income maturities, Cost or Amortized Cost	4,214.7	4,962.8
U.S. government
Schedule of Trading Securities and Other Trading Items [Line Items]
Short term investment, available for sale(amortized cost - $117.6 and $117.66)	1,101.2	1,413.1
Gross unrealized gains	60.5	31.3
Gross unrealized losses	(0.6)	(1.4)
Allowance for credit loss	0.0
Total, Available for sale investments in fixed income maturities, Cost or Amortized Cost	1,041.3	1,383.2
U.S. agency
Schedule of Trading Securities and Other Trading Items [Line Items]
Short term investment, available for sale(amortized cost - $117.6 and $117.66)	34.3	39.6
Gross unrealized gains	1.5	0.9
Gross unrealized losses	0.0	0.0
Allowance for credit loss	0.0
Total, Available for sale investments in fixed income maturities, Cost or Amortized Cost	32.8	38.7
Municipal
Schedule of Trading Securities and Other Trading Items [Line Items]
Short term investment, available for sale(amortized cost - $117.6 and $117.66)	67.1	50.7
Gross unrealized gains	5.5	2.9
Gross unrealized losses	0.0	0.0
Allowance for credit loss	0.0
Total, Available for sale investments in fixed income maturities, Cost or Amortized Cost	61.6	47.8
Corporate
Schedule of Trading Securities and Other Trading Items [Line Items]
Short term investment, available for sale(amortized cost - $117.6 and $117.66)	1,826.2	1,959.8
Gross unrealized gains	112.0	54.8
Gross unrealized losses	(0.1)	(0.6)
Allowance for credit loss	(0.2)
Total, Available for sale investments in fixed income maturities, Cost or Amortized Cost	1,714.5	1,905.6
Non-U.S. government-backed corporate
Schedule of Trading Securities and Other Trading Items [Line Items]
Short term investment, available for sale(amortized cost - $117.6 and $117.66)	63.4	86.5
Gross unrealized gains	0.7	0.5
Gross unrealized losses	0.0	(0.1)
Allowance for credit loss	0.0
Total, Available for sale investments in fixed income maturities, Cost or Amortized Cost	62.7	86.1
Non-U.S government
Schedule of Trading Securities and Other Trading Items [Line Items]
Short term investment, available for sale(amortized cost - $117.6 and $117.66)	273.1	328.8
Gross unrealized gains	4.3	4.5
Gross unrealized losses	0.0	(0.4)
Allowance for credit loss	0.0
Total, Available for sale investments in fixed income maturities, Cost or Amortized Cost	268.8	324.7
Asset-backed
Schedule of Trading Securities and Other Trading Items [Line Items]
Short term investment, available for sale(amortized cost - $117.6 and $117.66)	2.3	0.2
Gross unrealized gains	0.0	0.0
Gross unrealized losses	0.0	0.0
Allowance for credit loss	0.0
Total, Available for sale investments in fixed income maturities, Cost or Amortized Cost	2.3	0.2
Non-agency commercial mortgage-backed securities
Schedule of Trading Securities and Other Trading Items [Line Items]
Short term investment, available for sale(amortized cost - $117.6 and $117.66)	7.4	6.5
Gross unrealized gains	0.7	0.0
Gross unrealized losses	0.0	(0.2)
Allowance for credit loss	0.0
Total, Available for sale investments in fixed income maturities, Cost or Amortized Cost	6.7	6.7
Agency mortgage-backed
Schedule of Trading Securities and Other Trading Items [Line Items]
Short term investment, available for sale(amortized cost - $117.6 and $117.66)	973.1	1,073.0
Gross unrealized gains	37.2	21.9
Gross unrealized losses	(0.1)	(1.1)
Allowance for credit loss	0.0
Total, Available for sale investments in fixed income maturities, Cost or Amortized Cost	$ 936.0	$ 1,052.2

X

- Definition

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563

+ Details

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

X

- Definition

Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563

+ Details

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

X

- Definition

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=118942338&loc=SL82898722-210454

+ Details

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

X

- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=118942338&loc=SL82898722-210454

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118954083&loc=d3e26610-111562

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563

+ Details

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

X

- Definition

Amount of allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 50
-Paragraph 9
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118955579&loc=SL82922900-210455

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 50
-Paragraph 9
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=118955579&loc=SL82922900-210455

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aaa)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=118942338&loc=SL82898722-210454

+ Details

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

X

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

X

- Details

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

X

- Details

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

X

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_USTreasurySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_MunicipalBondsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_ForeignCorporateDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_ForeignGovernmentDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_AssetBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_FinancialInstrumentAxis=ahl_NonagencycommercialmortgagebackedsecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_MortgageBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: