Goodwill - Changes in Goodwill (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Goodwill [Roll Forward]
Goodwill gross, beginning balance	$ 22.1	$ 27.1
Accumulated impairment, beginning balance	(1.8)	(6.8)
Goodwill, beginning balance	20.3	20.3
Additions	0.0	0.0
Impairments	0.0	0.0
Disposals	0.0	0.0
Goodwill gross, ending balance	22.1	22.1
Accumulated impairment, ending balance	(1.8)	(1.8)
Goodwill, ending balance	20.3	20.3
Quant & Solutions
Goodwill [Roll Forward]
Goodwill gross, beginning balance	22.1	22.1
Accumulated impairment, beginning balance	(1.8)	(1.8)
Goodwill, beginning balance	20.3	20.3
Additions	0.0	0.0
Impairments	0.0	0.0
Disposals	0.0	0.0
Goodwill gross, ending balance	22.1	22.1
Accumulated impairment, ending balance	(1.8)	(1.8)
Goodwill, ending balance	20.3	20.3
Others
Goodwill [Roll Forward]
Goodwill gross, beginning balance	0.0	5.0
Accumulated impairment, beginning balance	0.0	(5.0)
Goodwill, beginning balance	0.0	0.0
Additions	0.0	0.0
Impairments	0.0	0.0
Disposals	0.0	0.0
Goodwill gross, ending balance	0.0	0.0
Accumulated impairment, ending balance	0.0	0.0
Goodwill, ending balance	$ 0.0	$ 0.0