Goodwill and Other Intangible Assets - Schedule of Goodwill and Other Intangible Assets Rollforward (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Acquired Finite-Lived Intangible Assets [Line Items]
Goodwill, beginning balance			$ 142.3
Amortization of other intangible assets	$ (1.0)	$ (0.5)	(2.0)	$ (1.1)
Goodwill, ending balance	201.8		201.8
Goodwill
Acquired Finite-Lived Intangible Assets [Line Items]
Goodwill, beginning balance	142.3	135.7	142.3	19.2
Acquisition of businesses	59.5	15.8	59.5	15.8
Measurement period adjustments			0.0	(0.3)
Amortization of other intangible assets	0.0	0.0	0.0	0.0
Goodwill, ending balance	201.8	151.5	201.8	151.5
Goodwill | Other
Acquired Finite-Lived Intangible Assets [Line Items]
Measurement period adjustments				0.2
Goodwill | Ark
Acquired Finite-Lived Intangible Assets [Line Items]
Goodwill acquired			0.0	116.8
Other
Acquired Finite-Lived Intangible Assets [Line Items]
Other intangible assets (excluding goodwill), beginning balance	197.2	201.6	198.2	26.4
Acquisition of businesses	0.0	0.0	0.0	0.0
Measurement period adjustments			0.0	0.1
Amortization of other intangible assets	(1.0)	(0.5)	(2.0)	(1.1)
Other intangible assets (excluding goodwill), ending balance	196.2	201.1	196.2	201.1
Other | Ark
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible assets acquired			0.0	175.7
Total Goodwill and Other Intangible Assets
Acquired Finite-Lived Intangible Assets [Line Items]
Other intangible assets, gross (including goodwill), beginning balance	339.5	337.3	340.5	45.6
Acquisition of businesses	59.5	15.8	59.5	15.8
Measurement period adjustments			0.0	(0.2)
Amortization of other intangible assets	(1.0)	(0.5)	(2.0)	(1.1)
Other intangible assets, gross (including goodwill), ending balance	$ 398.0	$ 352.6	398.0	352.6
Total Goodwill and Other Intangible Assets | Ark
Acquired Finite-Lived Intangible Assets [Line Items]
Goodwill and other intangible assets acquired			$ 0.0	$ 292.5