Share-Based Compensation Plans - Schedule of Compensation Costs by Performance Incentive Plan (Details) - Performance Shares - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
2015 Executive Performance Incentive Program
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Capitalized compensation cost	$ 0.0	$ 0.0	$ 2.2
2016 Executive Performance Incentive Program
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Capitalized compensation cost	0.0	2.1	4.4
2017 Executive Performance Incentive Program, Liability
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Capitalized compensation cost	(1.4)	1.0	1.7
2018 Executive Performance Incentive Program, Liability
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Capitalized compensation cost	(0.3)	0.6	0.0
2019 Executive Performance Incentive Program, Liability
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Capitalized compensation cost	$ 0.9	$ 0.0	$ 0.0