Goodwill and Other Intangible Assets - Schedule of Goodwill and Other Intangible Assets Rollforward (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Acquired Finite-Lived Intangible Assets [Line Items]
Goodwill, beginning balance			$ 394.7
Other intangible assets, impairments			(6.2)		$ (2.8)
Amortization of other intangible assets	$ 5.4	$ 4.6	17.1	$ 15.4
Goodwill, ending balance	540.1		540.1		394.7
Renewal rights
Acquired Finite-Lived Intangible Assets [Line Items]
Payments to acquire intangible assets		0.0		82.5
Goodwill
Acquired Finite-Lived Intangible Assets [Line Items]
Goodwill, beginning balance	518.2	428.6	394.7	379.9	379.9
Deconsolidation of business			0.0	(18.3)
Attribution of acquisition date fair value estimates between goodwill and other intangible assets	0.0	(2.2)	0.0	(29.0)
Acquisitions of businesses	14.9	0.0	140.0	93.8
Goodwill, foreign currency translation gain (loss)	7.0	(1.6)	5.2	(1.6)
Measurement period adjustments			0.2	0.0
Other intangible assets, impairments			0.0	0.0
Goodwill, ending balance	540.1	424.8	540.1	424.8	394.7
Goodwill | Renewal rights
Acquired Finite-Lived Intangible Assets [Line Items]
Payments to acquire intangible assets	0.0	0.0	0.0	0.0
Other Intangible Assets
Acquired Finite-Lived Intangible Assets [Line Items]
Other intangible assets (excluding goodwill), beginning balance	241.7	239.0	260.0	157.6	157.6
Deconsolidation of business			0.0	(23.5)
Attribution of acquisition date fair value estimates between goodwill and other intangible assets	0.0	2.2	0.0	29.0
Acquisitions of businesses	0.0	0.0	0.0	0.0
Other intangible assets, foreign currency translation gain (loss)	(0.1)	(0.5)	(0.5)	0.0
Measurement period adjustments			0.0	5.9
Other intangible assets, impairments			(6.2)	0.0
Amortization of other intangible assets			17.1	15.4
Other intangible assets (excluding goodwill), ending balance	236.2	236.1	236.2	236.1	260.0
Other Intangible Assets | Renewal rights
Acquired Finite-Lived Intangible Assets [Line Items]
Payments to acquire intangible assets	0.0	0.0	0.0	82.5
Total Goodwill and Other Intangible Assets
Acquired Finite-Lived Intangible Assets [Line Items]
Other intangible assets, gross (including goodwill), beginning balance	759.9	667.6	654.7	537.5	537.5
Deconsolidation of business			0.0	(41.8)
Attribution of acquisition date fair value estimates between goodwill and other intangible assets	0.0	0.0	0.0	0.0
Acquisitions of businesses	14.9	0.0	140.0	93.8
Other intangible assets, foreign currency translation gain (loss)	6.9	(2.1)	4.7	(1.6)
Measurement period adjustments			0.2	5.9
Other intangible assets, impairments			(6.2)	0.0
Amortization of other intangible assets	5.4	4.6	17.1	15.4
Other intangible assets, gross (including goodwill), ending balance	776.3	$ 660.9	776.3	$ 660.9	$ 654.7
Total Goodwill and Other Intangible Assets | Renewal rights
Acquired Finite-Lived Intangible Assets [Line Items]
Payments to acquire intangible assets	$ 0.0		$ 0.0