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Discontinued Operations (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
Discontinued Operations (Details) - USD ($) $ in Millions	Mar. 13, 2020	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash purchase price				$ 0.0	$ 1,159.4
Income (loss):
Income (loss) from discontinued operations, net of tax		$ 0.0	$ (2.1)	$ 0.0	1,066.4
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)	$ 1,159.4
Revenue			0.0		149.5
Income (loss):
Operations			0.1		9.1
Gain on sale			(0.9)		1,060.8
Income from discontinued operations			(0.8)		1,069.9
Income tax provision			1.3		3.5
Income (loss) from discontinued operations, net of tax			$ (2.1)		$ 1,066.4