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Goodwill and Other Intangible Assets (Goodwill and Intangible Assets Rollforward) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Goodwill [Roll Forward]
Beginning balance	$ 379.9
Ending balance	394.7	$ 379.9
Finite-lived Intangible Assets [Roll Forward]
Amortization	(21.8)	(18.8)	$ (10.7)
Goodwill and Intangible Assets [Roll Forward]
Purchases of consolidated subsidiaries, net of cash acquired	258.0	295.2	27.6
Goodwill, impairment loss	7.6
Other Intangible Assets
Goodwill [Roll Forward]
Measurement period adjustments(5)	26.8
Measurement period adjustments	5.9
Finite-lived Intangible Assets [Roll Forward]
Beginning balance	157.6	36.2
Acquisitions of businesses	34.6	140.9
Foreign currency translation	0.7	(0.7)
Amortization	(21.8)	(18.8)
Ending balance	260.0	157.6	36.2
Goodwill and Intangible Assets [Roll Forward]
Impairments	2.8
Renewal Rights
Finite-lived Intangible Assets [Roll Forward]
Acquisitions of businesses	82.5
Goodwill
Goodwill [Roll Forward]
Beginning balance	379.9	25.9
Acquisitions of businesses	64.8	356.5
Dispositions of businesses (2)	(18.3)
Measurement period adjustments(5)	(26.8)
Write-off	(7.6)
Measurement period adjustments	0.9
Foreign currency translation	1.8	(2.5)
Ending balance	394.7	379.9	25.9
Intangible Asset and Goodwill
Goodwill [Roll Forward]
Dispositions of businesses (2)	(41.8)
Measurement period adjustments	6.8
Finite-lived Intangible Assets [Roll Forward]
Acquisitions of businesses	99.4	497.4
Foreign currency translation	2.5	(3.2)
Amortization	(21.8)	(18.8)
Goodwill and Intangible Assets [Roll Forward]
Beginning balance	537.5	62.1
Write-off	(10.4)
Ending balance	654.7	537.5	62.1
Intangible Asset and Goodwill | Renewal Rights
Finite-lived Intangible Assets [Roll Forward]
Acquisitions of businesses	82.5
MediaAlpha | Other Intangible Assets
Goodwill [Roll Forward]
Dispositions of businesses (2)	(23.5)
Finite-lived Intangible Assets [Roll Forward]
Write-off	(2.8)
Other Operations
Goodwill and Intangible Assets [Roll Forward]
Goodwill, impairment loss	7.6
Impairments	0.4
NSM Holding Co LLC
Goodwill [Roll Forward]
Beginning balance	354.3
Ending balance	381.6	354.3
Finite-lived Intangible Assets [Roll Forward]
Amortization	(19.4)	(8.3)	$ 0.0
Goodwill and Intangible Assets [Roll Forward]
Impairments	2.4
NSM Holding Co LLC | Renewal Rights
Goodwill and Intangible Assets [Roll Forward]
Impairments	0.0
NSM Holding Co LLC | Goodwill
Goodwill [Roll Forward]
Foreign currency translation	1.4	$ (2.2)
Fresh Insurance Services Group Limited
Goodwill and Intangible Assets [Roll Forward]
Impairments	2.4
KBK Insurance Group, Inc. & KBK Premium Services, Inc. | Goodwill
Goodwill [Roll Forward]
Measurement period adjustments(5)	$ 5.9

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The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

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