Acquisitions and Divestitures - Additional Information (Details) - Allied World $ in Millions	12 Months Ended
Dec. 31, 2017 USD ($)
Disclosure of detailed information about business combination [line items]
Contributed revenue from acquiree	$ 1,050.5
Net loss from acquiree	555.4
Pro forma revenue	17,514.6
Pro forma net earnings	$ 1,766.4

Profit (Loss) Of Acquirees As If Combination Occurred At Beginning Of Period

No definition available.

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- Definition

Revenue Of Acquirees As If Combination Occurred At Beginning Of Period

+ References

No definition available.

+ Details

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- Definition

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

+ References

No definition available.

+ Details

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- Definition

The profit (loss) of the combined entity as though the acquisition date for all business combinations that occurred during the year had been as of the beginning of the annual reporting period. [Refer: Business combinations [member]; Profit (loss)]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 3
-IssueDate 2018-01-01
-Paragraph B64
-Subparagraph q
-Clause ii
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=3&date=2018-03-01&anchor=para_B64_q_ii&doctype=Appendix&seq=2
-URIDate 2018-03-16

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- Definition

The revenue of the combined entity as though the acquisition date for all business combinations that occurred during the year had been as of the beginning of the annual reporting period. [Refer: Business combinations [member]; Revenue]

+ References

+ Details

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