Selected Quarterly Financial Data (unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 162.9	$ 117.9	$ 133.3	$ 109.7	$ 120.8	$ 127.5	$ 122.6	$ 128.6	$ 523.8	$ 499.5	$ 594.6
Operating income	48.5	28.7	36.1	32.5	26.9	34.2	29.9	40.7	145.8	131.7	222.2
Income from continuing operations before income taxes	58.5	57.4	34.6	27.6	265.3	41.2	36.0	2.3
Income from discontinued operations, net of tax	0.8	1.2	53.4	21.9	15.7	2.1	26.7	23.3	77.3	67.8	37.3
Gain on disposal of discontinued operations, net of tax	(3.6)	185.4	509.2	0.0					691.0	0.0	0.0
Net income	39.2	229.5	587.3	40.4	205.5	34.0	53.9	22.1	$ 896.4	$ 315.5	$ 240.0
Net income attributable to controlling interests	$ 39.2	$ 229.5	$ 532.7	$ 27.0	$ 198.0	$ 37.2	$ 18.9	$ 32.6
Earnings per share (basic) attributable to controlling interests (in dollars per share)	$ 0.55	$ 2.88	$ 6.71	$ 0.34	$ 2.49	$ 0.46	$ 0.23	$ 0.38	$ 10.73	$ 3.53	$ 2.45
Earnings per share (diluted) attributable to controlling interests (in dollars per share)	0.53	2.76	6.42	0.33	2.42	0.46	0.23	0.38	10.29	3.49	2.45
Continuing operations earnings per share (basic) attributable to controlling interests (in dollars per share)	0.59	0.54	0.31	0.23	2.36	0.36	0.26	0.06	1.66	3.04	2.16
Continuing operations earnings per share (diluted) attributable to controlling interests (in dollars per share)	$ 0.57	$ 0.52	$ 0.29	$ 0.22	$ 2.30	$ 0.36	$ 0.26	$ 0.09	$ 1.59	$ 3.01	$ 2.16
Weighted average shares outstanding (in shares)	70,600,000	79,600,000	79,400,000	79,300,000	79,600,000	80,000,000.0	80,400,000	85,100,000	77,213,010	81,259,778	91,205,412
Weighted average diluted shares outstanding (in shares)	73,500,000	83,200,000	82,900,000	82,300,000	81,800,000	80,900,000	80,400,000	85,100,000	80,485,924	82,036,203	91,268,952