New Accounting Pronouncements (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2018	Jun. 30, 2020	Sep. 30, 2019	Jun. 30, 2019
Cumulative effect of adoption
Stockholders' equity, including portion attributable to noncontrolling interest	$ 2,631.7	$ 1,851.9	$ 731.2	$ 1,504.9	$ 1,939.4	$ 1,891.7
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member	us-gaap:AccountingStandardsUpdate201613Member	us-gaap:AccountingStandardsUpdate201602Member
Cumulative Effect, Period of Adoption, Adjustment
Cumulative effect of adoption
Stockholders' equity, including portion attributable to noncontrolling interest		$ 0.6	$ 1,085.7
Retained Earnings (Accum- ulated Deficit)
Cumulative effect of adoption
Stockholders' equity, including portion attributable to noncontrolling interest	$ (518.4)	161.6	(968.0)	$ (660.3)	$ 254.1	$ 210.2
Retained Earnings (Accum- ulated Deficit) | Cumulative Effect, Period of Adoption, Adjustment
Cumulative effect of adoption
Stockholders' equity, including portion attributable to noncontrolling interest		$ 0.6	$ 1,085.7