Segments (Goodwill Rollforward) (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2015 USD ($)
Goodwill [Line Items]
Balance at beginning of year	$ 905,636
Acquisition of ProAg	47,145
Other, principally foreign exchange	(651)
Balance at June 30, 2015	952,130
North America Property & Casualty [Member]
Goodwill [Line Items]
Balance at beginning of year	552,006
Acquisition of ProAg	47,145
Other, principally foreign exchange	99
Balance at June 30, 2015	599,250
Accident & Health [Member]
Goodwill [Line Items]
Balance at beginning of year	144,113
Acquisition of ProAg	0
Other, principally foreign exchange	0
Balance at June 30, 2015	144,113
International [Member]
Goodwill [Line Items]
Balance at beginning of year	209,517
Acquisition of ProAg	0
Other, principally foreign exchange	(750)
Balance at June 30, 2015	$ 208,767