Equity Method Investment, Aggregate Cost [Roll Forward]

No definition available.

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Namespace Prefix:	ahl_
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- Definition

This element represents the aggregate cost of investments accounted for under the equity method of accounting.

+ 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 210.5-02.12)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

This item represents the amount of unrealized intercompany profits and losses on transactions between the Entity and unconsolidated subsidiaries (including certain corporate joint ventures, and noncontrolled corporations), accounted for under the equity method of accounting, which have not been eliminated in preparing the Entity's financial statements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section S99
-Paragraph 4
-Subparagraph (SX 210.3A-04)
-URI http://asc.fasb.org/extlink&oid=27015204&loc=d3e355119-122828

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 35
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=99375318&loc=d3e32367-111569

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

+ Details

Name:	us-gaap_GoodwillAcquiredDuringPeriod
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The net cash outflow or inflow associated with the acquisition or sale of a business segment during the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3213-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3179-108585

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The cash inflow associated with the sale of equity method investments, which are investments in joint ventures and entities in which the entity has an equity ownership interest normally of 20 to 50 percent and exercises significant influence.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3179-108585

+ Details

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

- Details

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Investments - Other Investments (Details) - USD ($) $ in Millions		1 Months Ended	12 Months Ended
	Jul. 26, 2016	Jan. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Equity Method Investment, Aggregate Cost [Roll Forward]
Opening undistributed value of investment, beginning balance			$ 12.1	$ 8.9
Investment in the period			64.9	3.3
Goodwill			(1.8)
Proceeds from sale of equity method investments			(9.3)	0.0	$ 0.0
Unrealized gain/(loss) for the period			0.5	(0.1)
Closing value of investment, ending balance			66.4	12.1	8.9
MVI
Equity Method Investment, Aggregate Cost [Roll Forward]
Opening undistributed value of investment, beginning balance			0.5	0.8
Investment in the period		$ 0.8	0.1	0.0
Goodwill			0.0
Proceeds from sale of equity method investments			0.0
Unrealized gain/(loss) for the period			(0.1)	(0.3)
Closing value of investment, ending balance			0.5	0.5	0.8
Chaspark
Equity Method Investment, Aggregate Cost [Roll Forward]
Opening undistributed value of investment, beginning balance			8.4	8.1
Investment in the period			0.0	0.0
Goodwill			0.0
Proceeds from sale of equity method investments			(9.3)
Unrealized gain/(loss) for the period			0.9	0.3
Closing value of investment, ending balance			0.0	8.4	8.1
Bene
Equity Method Investment, Aggregate Cost [Roll Forward]
Opening undistributed value of investment, beginning balance			3.2	0.0
Investment in the period	$ 3.3		0.0	3.3
Goodwill			0.0
Proceeds from sale of equity method investments			0.0
Unrealized gain/(loss) for the period			(0.3)	(0.1)
Closing value of investment, ending balance			2.9	3.2	0.0
Digital Re
Equity Method Investment, Aggregate Cost [Roll Forward]
Opening undistributed value of investment, beginning balance			0.0	0.0
Investment in the period			2.3	0.0
Goodwill			(1.8)
Proceeds from sale of equity method investments			0.0
Unrealized gain/(loss) for the period			0.0	0.0
Closing value of investment, ending balance			0.5	0.0	0.0
Crop Re
Equity Method Investment, Aggregate Cost [Roll Forward]
Opening undistributed value of investment, beginning balance			0.0	0.0
Investment in the period			62.5	0.0
Goodwill			0.0
Proceeds from sale of equity method investments			0.0
Unrealized gain/(loss) for the period			0.0	0.0
Closing value of investment, ending balance			$ 62.5	$ 0.0	$ 0.0