Segments (Goodwill Rollforward) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Dec. 31, 2014
Goodwill [Line Items]
Balance at beginning of year	$ 905,636us-gaap_Goodwill
Acquisition of ProAg	45,000us-gaap_GoodwillAcquiredDuringPeriod
Other, principally foreign exchange	(1,285)
Balance at March 31, 2015	949,351us-gaap_Goodwill
North America Property & Casualty [Member]
Goodwill [Line Items]
Balance at beginning of year	552,006
Acquisition of ProAg	45,000
Other, principally foreign exchange	100
Balance at March 31, 2015	597,106
Accident & Health [Member]
Goodwill [Line Items]
Balance at beginning of year		144,113
Balance at March 31, 2015	144,113	144,113
International [Member]
Goodwill [Line Items]
Balance at beginning of year	209,517
Other, principally foreign exchange	(1,385)
Balance at March 31, 2015	$ 208,132

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 20

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 20

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266

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Amount of increase (decrease) from adjustments after acquisition date under purchase accounting of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ 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 (g)

-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 10

-Section 25

-Paragraph 16

-URI http://asc.fasb.org/extlink&oid=34752592&loc=d3e961-128460

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