Goodwill and Other Intangible Assets - Schedule of Goodwill and Other Intangible Assets Rollforward (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2018
Goodwill [Line Items]
Goodwill, acquisition date fair value	$ 518.2		$ 518.2		$ 402.3
Goodwill, Impairment Loss					7.6
Goodwill	518.2		518.2		394.7
Other intangible assets, acquisition date fair value	806.0		806.0		694.4
Other intangible assets, accumulated amortization	39.9		39.9		29.3
Impairment of Intangible Assets, Finite-lived					(10.4)
Goodwill and intangible assets, net carrying value	759.9		759.9		654.7
Payments to Acquire Intangible Assets		$ 82.5		$ 82.5
NSM Holding Co LLC
Goodwill [Line Items]
Goodwill, acquisition date fair value	504.9		504.9		381.6
Goodwill	504.9		504.9		381.6
Other intangible assets, acquisition date fair value	268.6		268.6		271.7
Other intangible assets, accumulated amortization	38.7		38.7		27.9
Impairment of Intangible Assets, Finite-lived					(2.4)
Other intangible assets, net carrying value	223.7		223.7		241.4
Amortization of Intangible Assets	(6.3)	(4.1)	(11.1)	(9.1)
Kudu investments
Goodwill [Line Items]
Goodwill, acquisition date fair value	7.6		7.6		7.6
Goodwill	7.6		7.6		7.6
Amortization of Intangible Assets	(0.1)	0.0	(0.2)	0.0
Other
Goodwill [Line Items]
Goodwill, acquisition date fair value	5.7		5.7		13.1
Goodwill, Impairment Loss					7.6
Goodwill	5.7		5.7		5.5
Other intangible assets, acquisition date fair value	17.0		17.0		18.2
Other intangible assets, accumulated amortization	0.8		0.8		1.2
Impairment of Intangible Assets, Finite-lived					(0.4)
Other intangible assets, net carrying value	16.2		16.2		16.6
Customer relationships | NSM Holding Co LLC
Goodwill [Line Items]
Other intangible assets, acquisition date fair value	120.1		120.1		121.7
Other intangible assets, accumulated amortization	26.9		26.9		19.8
Impairment of Intangible Assets, Finite-lived					(1.4)
Other intangible assets, net carrying value	89.7		$ 89.7		100.5
Acquired finite-lived intangible assets, weighted average useful life			9 years
Customer relationships | Other
Goodwill [Line Items]
Other intangible assets, acquisition date fair value	7.2		$ 7.2		7.2
Other intangible assets, accumulated amortization	0.6		0.6		0.4
Impairment of Intangible Assets, Finite-lived					0.0
Other intangible assets, net carrying value	6.6		$ 6.6		6.8
Acquired finite-lived intangible assets, weighted average useful life			11 years
Trade names | NSM Holding Co LLC
Goodwill [Line Items]
Other intangible assets, acquisition date fair value	61.2		$ 61.2		61.9
Other intangible assets, accumulated amortization	6.6		6.6		5.3
Impairment of Intangible Assets, Finite-lived					(0.4)
Other intangible assets, net carrying value	53.6		$ 53.6		56.2
Acquired finite-lived intangible assets, weighted average useful life			19 years
Trade names | Kudu investments
Goodwill [Line Items]
Other intangible assets, acquisition date fair value	2.2		$ 2.2		2.2
Other intangible assets, accumulated amortization	0.4		0.4		0.2
Impairment of Intangible Assets, Finite-lived					0.0
Other intangible assets, net carrying value	1.8		$ 1.8		2.0
Acquired finite-lived intangible assets, weighted average useful life			7 years
Trade names | Other
Goodwill [Line Items]
Other intangible assets, acquisition date fair value	1.0		$ 1.0		1.7
Other intangible assets, accumulated amortization	0.1		0.1		0.5
Impairment of Intangible Assets, Finite-lived					(0.2)
Other intangible assets, net carrying value	0.9		$ 0.9		1.0
Acquired finite-lived intangible assets, weighted average useful life			10 years
Information technology | NSM Holding Co LLC
Goodwill [Line Items]
Other intangible assets, acquisition date fair value	3.1		$ 3.1		3.9
Other intangible assets, accumulated amortization	1.4		1.4		1.4
Impairment of Intangible Assets, Finite-lived					(0.6)
Other intangible assets, net carrying value	0.0		0.0		1.9
Information technology | Other
Goodwill [Line Items]
Other intangible assets, acquisition date fair value	0.0		0.0		0.5
Other intangible assets, accumulated amortization	0.0		0.0		0.3
Impairment of Intangible Assets, Finite-lived					(0.2)
Other intangible assets, net carrying value	0.0		$ 0.0		0.0
Acquired finite-lived intangible assets, weighted average useful life			5 years
Other | NSM Holding Co LLC
Goodwill [Line Items]
Other intangible assets, acquisition date fair value	1.7		$ 1.7		1.7
Other intangible assets, accumulated amortization	1.0		1.0		0.7
Impairment of Intangible Assets, Finite-lived					0.0
Other intangible assets, net carrying value	0.7		$ 0.7		1.0
Acquired finite-lived intangible assets, weighted average useful life			3 years
Other | Other
Goodwill [Line Items]
Other intangible assets, acquisition date fair value	0.2		$ 0.2		0.2
Other intangible assets, accumulated amortization	0.1		0.1		0.0
Impairment of Intangible Assets, Finite-lived					0.0
Other intangible assets, net carrying value	0.1		$ 0.1		0.2
Acquired finite-lived intangible assets, weighted average useful life			5 years
Renewal Rights
Goodwill [Line Items]
Acquisitions of businesses			$ 0.0
Payments to Acquire Intangible Assets		82.5		82.5
Renewal Rights | NSM Holding Co LLC
Goodwill [Line Items]
Other intangible assets, acquisition date fair value	82.5		82.5		82.5
Other intangible assets, accumulated amortization	2.8		2.8		0.7
Impairment of Intangible Assets, Finite-lived					0.0
Other intangible assets, net carrying value	79.7		$ 79.7		81.8
Acquired finite-lived intangible assets, weighted average useful life			12 years
Other Intangible Assets
Goodwill [Line Items]
Foreign currency translation	0.1	0.2	$ (0.4)	0.5
Measurement Period Adjustments	0.0	0.0	0.0	5.9
Intangible Assets, Net (Excluding Goodwill)	241.7	239.0	241.7	239.0	260.0	$ 254.4	$ 160.5	$ 157.6
Other intangible assets, acquisition date fair value	287.8		287.8		292.1
Other intangible assets, accumulated amortization	39.9		39.9		29.3
Impairment of Intangible Assets, Finite-lived	(6.2)		(6.2)		(2.8)
Other intangible assets, net carrying value	241.7		241.7		260.0
Deconsolidation of Business				(23.5)
Amortization of Intangible Assets	(6.6)	(4.2)	(11.7)	(10.8)
Goodwill, Acquired During Period			0.0	0.0
Acquisitions of businesses	0.0	0.0	0.0	26.8
Licensing Agreements [Member] | Other
Goodwill [Line Items]
Other intangible assets, acquisition date fair value	8.6		8.6		8.6
Other intangible assets, accumulated amortization	0.0		0.0		0.0
Impairment of Intangible Assets, Finite-lived					0.0
Other intangible assets, net carrying value	8.6		8.6		8.6
Non-controlling interest
Goodwill [Line Items]
Goodwill and intangible assets, net carrying value	(25.9)		(25.9)		(23.4)
Total
Goodwill [Line Items]
Goodwill and intangible assets, net carrying value	734.0		734.0		631.3
Goodwill
Goodwill [Line Items]
Measurement Period Adjustments	0.0	(0.3)	0.2
Goodwill	518.2	428.6	518.2	428.6	394.7	392.4	349.7	379.9
Deconsolidation of Business				(18.3)
Goodwill, Acquired During Period	125.1	80.4	125.1	93.8
Acquisitions of businesses			0.0	(26.8)
Foreign currency translation	0.7	(1.2)	(1.8)	0.0
Intangible Asset and Goodwill
Goodwill [Line Items]
Foreign currency translation	0.8	(1.0)	(2.2)	0.5
Measurement Period Adjustments	0.0	(0.3)	0.2	5.9
Impairment of Intangible Assets, Finite-lived	(6.2)		(6.2)
Goodwill and intangible assets, acquisition date fair value	759.9	667.6	759.9	667.6	654.7	$ 646.8	$ 510.2	$ 537.5
Deconsolidation of Business				(41.8)
Amortization of Intangible Assets	(6.6)	(4.2)	(11.7)	(10.8)
Goodwill, Acquired During Period			125.1	93.8
Acquisitions of businesses	$ 125.1	$ 80.4	0.0	$ 0.0
Other Intangible Assets | NSM Holding Co LLC
Goodwill [Line Items]
Foreign currency translation			(0.4)		$ 0.7
Fresh Insurance Services Group Limited
Goodwill [Line Items]
Impairment of Intangible Assets, Finite-lived			(6.2)
Fresh Insurance Services Group Limited | NSM Holding Co LLC
Goodwill [Line Items]
Impairment of Intangible Assets, Finite-lived			(6.2)
Fresh Insurance Services Group Limited | Customer relationships | NSM Holding Co LLC
Goodwill [Line Items]
Impairment of Intangible Assets, Finite-lived			(3.5)
Fresh Insurance Services Group Limited | Trade names | NSM Holding Co LLC
Goodwill [Line Items]
Impairment of Intangible Assets, Finite-lived			(1.0)
Fresh Insurance Services Group Limited | Information technology | NSM Holding Co LLC
Goodwill [Line Items]
Impairment of Intangible Assets, Finite-lived			(1.7)
Fresh Insurance Services Group Limited | Other | NSM Holding Co LLC
Goodwill [Line Items]
Impairment of Intangible Assets, Finite-lived			0.0
Fresh Insurance Services Group Limited | Renewal Rights | NSM Holding Co LLC
Goodwill [Line Items]
Impairment of Intangible Assets, Finite-lived			0.0
Fresh Insurance Services Group Limited | Other Intangible Assets
Goodwill [Line Items]
Impairment of Intangible Assets, Finite-lived			$ (6.2)