Recently Issued Accounting Pronouncements & Updates to Accounting Policies (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Jan. 01, 2020	Dec. 31, 2019		Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member
Decrease in stockholder's equity	$ (1,864.5)	$ (1,730.0)		$ (1,781.1)	[1]	$ (1,893.4)	$ (1,929.0)	$ (1,746.7)
Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease in stockholder's equity			$ 2.2	2.2
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease in stockholder's equity	(714.2)	(756.7)		(811.1)		(925.0)	(959.9)	(862.6)
Retained Earnings | Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease in stockholder's equity			7.9	7.9
Accumulated Other Comprehensive Income (Loss)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease in stockholder's equity	$ (36.9)	$ (5.9)		(2.8)		$ (4.7)	$ (8.9)	$ 78.1
Accumulated Other Comprehensive Income (Loss) | Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease in stockholder's equity			$ 5.7	$ (5.7)

[1] Derived from audited consolidated financial statements.