Discontinued Operations (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
	Mar. 13, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash purchase price				$ 0.0	$ 1,162.9
Income (loss):
Income from discontinued operations, net of tax		$ 0.0	$ 0.4	$ 0.0	1,066.8
U.S. Federal Business | Discontinued Operations, 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			0.0		149.5
Income (loss):
Operations			0.0		9.1
Gain on sale			(0.2)		1,060.6
Income from discontinued operations			(0.2)		1,069.7
Income tax provision (benefit)			(0.6)		2.9
Income from discontinued operations, net of tax			$ 0.4		$ 1,066.8