Discontinued Operations (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
	Mar. 13, 2020	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash purchase price										$ 1,162.9	$ 0.0	$ 0.0
Income (loss)
Income from discontinued operations, net of tax		$ 1.6	$ 0.4	$ (2.1)	$ 1,068.5	$ 20.2	$ 16.0	$ 25.5	$ 13.3	1,068.4	75.0	53.9
U.S. Federal Business | Discontinued Operation, Disposed of by Sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash purchase price	$ 1,200.0
Net cash proceeds of the sale (net of working capital adjustments and transaction costs)	$ 1,162.9
Revenue										149.5	725.9	573.8
Income (loss)
Operations										8.4	100.3	72.2
Gain on sale										1,060.7	0.0	0.0
Income (loss) from discontinued operation										1,069.1	100.3	72.2
Income tax provision										0.7	25.3	18.3
Income from discontinued operations, net of tax										$ 1,068.4	$ 75.0	$ 53.9