Summary of Significant Accounting Policies (Schedule of Prior Year Amounts Recast Affected by Cumulative Adjustment in Balance Sheet) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Error Corrections And Prior Period Adjustments Restatement [Line Items]
Current assets of discontinued operations		$ 244.3
Total current assets	$ 244.4	717.6
Total assets	1,493.3	1,838.3
Retained earnings	1,008.2	829.8	$ 598.2
Total shareholders' equity	364.9	226.0	384.1	$ 266.4
Total liabilities and shareholders' equity	$ 1,493.3	1,838.3
As Reported [Member]
Error Corrections And Prior Period Adjustments Restatement [Line Items]
Current assets of discontinued operations		279.5
Total current assets		752.8
Total assets		1,873.5
Retained earnings		865.0	633.4
Total shareholders' equity		261.2	$ 419.3
Total liabilities and shareholders' equity		$ 1,873.5