Non-controlling Interests (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Noncontrolling Interest [Line Items]
Total non-controlling interests	$ (98.5)	$ (116.8)
Total Non-Controlling Excluding Reciprocals
Noncontrolling Interest [Line Items]
Total non-controlling interests	$ 31.9	$ 29.9
HG Global
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	3.10%	3.10%
Total non-controlling interests	$ 14.1	$ 14.4
Specialty Insurance Distribution (NSM)
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	3.40%	3.60%
Total non-controlling interests	$ 16.9	$ 14.9
Kudu
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	0.80%	0.90%
Total non-controlling interests	$ 2.2	$ 2.2
Other
Noncontrolling Interest [Line Items]
Total non-controlling interests	$ (1.3)	$ (1.6)
Build America Mutual
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	100.00%	100.00%
Total non-controlling interests	$ (130.4)	$ (146.7)