Non-controlling Interests (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Noncontrolling Interest [Line Items]
Total non-controlling interests	$ (143.7)	$ (124.9)
Total Non-Controlling Excluding Reciprocals
Noncontrolling Interest [Line Items]
Total non-controlling interests	$ 30.1	$ 45.7
HG Global
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	3.10%	3.10%
Total non-controlling interests	$ 14.8	$ 14.5
NSM Holding Co LLC
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	4.70%	4.50%
Total non-controlling interests	$ 14.2	$ 13.6
Other NSM
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	13.40%	13.40%
Total non-controlling interests	$ 0.2	$ 0.3
MediaAlpha
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	0.00%	39.00%
Total non-controlling interests	$ 0.0	$ 16.2
Other Operations
Noncontrolling Interest [Line Items]
Total non-controlling interests	$ 0.9	$ 1.1
Build America Mutual
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	100.00%	100.00%
Total non-controlling interests	$ (173.8)	$ (170.6)