New Accounting Standards (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018	Dec. 31, 2017
New Accounting Pronouncements [Abstract]
Stockholders' equity	$ 9,189.5	$ 1,869.9		$ 1,676.0	$ 1,476.8
Operating right-of-use asset	157.9	53.8
Operating lease liability	159.2	58.1
Accounting Standards Update 2016-02
New Accounting Pronouncements [Abstract]
Operating right-of-use asset			$ 61.3
Operating lease liability			$ 61.4
Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements [Abstract]
Stockholders' equity		(1.0)		0.0	0.0
Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2016-13 | Accounts Receivable
New Accounting Pronouncements [Abstract]
Stockholders' equity		(1.0)
Accumulated Deficit
New Accounting Pronouncements [Abstract]
Stockholders' equity	$ (175.7)	(141.4)		(308.7)	(577.8)
Accumulated Deficit | Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements [Abstract]
Stockholders' equity		(1.0)		$ 8.2	$ (0.3)
Accumulated Deficit | Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2016-13
New Accounting Pronouncements [Abstract]
Stockholders' equity		$ (1.0)