Goodwill and Other Intangible Assets (Summary of Goodwill and Intangible Assets) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Goodwill [Line Items]
Goodwill, fair value	$ 402.3	$ 379.9
Goodwill, impairment loss	7.6
Goodwill	394.7	379.9
Other intangible assets, fair value	694.4	591.1
Other intangible assets, accumulated amortization	29.3	53.6
Other intangible assets, net	251.4
Goodwill and Intangible Asset Impairment	10.4
Goodwill and other intangible assets	654.7	537.5
NSM Holding Co LLC
Goodwill [Line Items]
Goodwill, fair value	381.6	354.3
Goodwill	381.6	354.3
Other intangible assets, fair value	271.7	140.2
Other intangible assets, accumulated amortization	27.9	8.3
Impairments	2.4
Other intangible assets, net	241.4	131.9
Kudu
Goodwill [Line Items]
Goodwill, fair value	7.6	0.0
Goodwill	7.6	0.0
MediaAlpha
Goodwill [Line Items]
Goodwill, fair value	0.0	18.3
Goodwill	0.0	18.3
Other intangible assets, fair value	0.0	69.9
Other intangible assets, accumulated amortization	0.0	44.8
Impairments	0.0
Other intangible assets, net	0.0	25.1
Other
Goodwill [Line Items]
Goodwill, fair value	13.1	7.3
Goodwill, impairment loss	7.6
Goodwill	5.5	7.3
Other intangible assets, fair value	18.2	1.1
Other intangible assets, accumulated amortization	1.2	0.5
Impairments	0.4
Other intangible assets, net	$ 16.6	0.6
Customer Relationships | NSM Holding Co LLC
Goodwill [Line Items]
Acquired other intangible assets, weighted average useful life	9 years
Other intangible assets, fair value	$ 121.7	85.3
Other intangible assets, accumulated amortization	19.8	6.0
Impairments	1.4
Other intangible assets, net	$ 100.5	79.3
Customer Relationships | MediaAlpha
Goodwill [Line Items]
Acquired other intangible assets, weighted average useful life	9 years
Other intangible assets, fair value	$ 0.0	26.8
Other intangible assets, accumulated amortization	0.0	4.9
Impairments	0.0
Other intangible assets, net	$ 0.0	21.9
Customer Relationships | Other
Goodwill [Line Items]
Acquired other intangible assets, weighted average useful life	11 years
Other intangible assets, fair value	$ 7.2	0.0
Other intangible assets, accumulated amortization	0.4	0.0
Other intangible assets, net	$ 6.8	0.0
Trade Names | NSM Holding Co LLC
Goodwill [Line Items]
Acquired other intangible assets, weighted average useful life	19 years
Other intangible assets, fair value	$ 61.9	51.2
Other intangible assets, accumulated amortization	5.3	1.8
Impairments	0.4
Other intangible assets, net	$ 56.2	49.4
Trade Names | Kudu
Goodwill [Line Items]
Acquired other intangible assets, weighted average useful life	7 years
Other intangible assets, fair value	$ 2.2	0.0
Other intangible assets, accumulated amortization	0.2	0.0
Impairments	0.0
Other intangible assets, net	$ 2.0	0.0
Trade Names | Other
Goodwill [Line Items]
Acquired other intangible assets, weighted average useful life	10 years
Other intangible assets, fair value	$ 1.7	0.6
Other intangible assets, accumulated amortization	0.5	0.2
Impairments	0.2
Other intangible assets, net	$ 1.0	0.4
Information Technology | NSM Holding Co LLC
Goodwill [Line Items]
Acquired other intangible assets, weighted average useful life	5 years
Other intangible assets, fair value	$ 3.9	3.7
Other intangible assets, accumulated amortization	1.4	0.5
Impairments	0.6
Other intangible assets, net	$ 1.9	3.2
Information Technology | MediaAlpha
Goodwill [Line Items]
Acquired other intangible assets, weighted average useful life	5 years
Other intangible assets, fair value	$ 0.0	33.3
Other intangible assets, accumulated amortization	0.0	30.9
Impairments	0.0
Other intangible assets, net	$ 0.0	2.4
Information Technology | Other
Goodwill [Line Items]
Acquired other intangible assets, weighted average useful life	5 years
Other intangible assets, fair value	$ 0.5	0.5
Other intangible assets, accumulated amortization	0.3	0.3
Impairments	0.2
Other intangible assets, net		0.2
Insurance licenses | Other
Goodwill [Line Items]
Other intangible assets, fair value	8.6	0.0
Other intangible assets, accumulated amortization	0.0	0.0
Other intangible assets, net	$ 8.6	0.0
Renewal Rights | NSM Holding Co LLC
Goodwill [Line Items]
Acquired other intangible assets, weighted average useful life	12 years
Other intangible assets, fair value	$ 82.5
Other intangible assets, accumulated amortization	0.7
Impairments	0.0
Other intangible assets, net	$ 81.8
Other | NSM Holding Co LLC
Goodwill [Line Items]
Acquired other intangible assets, weighted average useful life	3 years
Other intangible assets, fair value	$ 1.7
Other intangible assets, accumulated amortization	0.7
Impairments	0.0
Other intangible assets, net	$ 1.0
Other | MediaAlpha
Goodwill [Line Items]
Acquired other intangible assets, weighted average useful life	3 years
Other intangible assets, fair value	$ 0.0	9.8
Other intangible assets, accumulated amortization	0.0	9.0
Impairments	0.0
Other intangible assets, net	$ 0.0	0.8
Other | Other
Goodwill [Line Items]
Acquired other intangible assets, weighted average useful life	5 years
Other intangible assets, fair value	$ 0.2	0.0
Other intangible assets, accumulated amortization	0.0	0.0
Other intangible assets, net	0.2	0.0
Other Intangible Assets
Goodwill [Line Items]
Other intangible assets, fair value	292.1	211.2
Other intangible assets, accumulated amortization	29.3	53.6
Impairments	2.8
Other intangible assets, net	260.0	157.6
Non-controlling Interests
Goodwill [Line Items]
Goodwill and other intangible assets	(23.4)	(40.6)
Parent
Goodwill [Line Items]
Goodwill and other intangible assets	631.3	496.9
Goodwill
Goodwill [Line Items]
Goodwill	394.7	379.9	$ 25.9
Goodwill, foreign currency translation gain	1.8	(2.5)
Goodwill | NSM Holding Co LLC
Goodwill [Line Items]
Goodwill, foreign currency translation gain	1.4	(2.2)
Goodwill | Other
Goodwill [Line Items]
Goodwill, foreign currency translation gain	0.0	(0.3)
Other Intangible Assets | NSM Holding Co LLC
Goodwill [Line Items]
Goodwill, foreign currency translation gain	$ 0.7	$ (0.7)