Non-controlling Interests (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Noncontrolling Interest [Line Items]
Total non-controlling interests	$ (102.7)	$ (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	$ 14.7	$ 14.4
NSM Holding Co LLC
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	3.40%	3.60%
Total non-controlling interests	$ 16.7	$ 14.9
Other NSM
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	13.40%	13.40%
Total non-controlling interests	$ (0.1)	$ (0.1)
Kudu Investment Management, LLC
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	0.80%	0.90%
Total non-controlling interests	$ 2.4	$ 2.2
Other Operations
Noncontrolling Interest [Line Items]
Total non-controlling interests	$ (1.8)	$ (1.5)
Build America Mutual
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	100.00%	100.00%
Total non-controlling interests	$ (134.6)	$ (146.7)