Income Taxes (Deferred Tax Assets (Liabilities) Classification) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Other assets	$ 212.6	$ 203.8
Total deferred tax assets	212.6	203.8
Deferred tax liabilities:
Long-term income taxes	(19.6)	(22.3)
Total deferred tax liabilities	(19.6)	(22.3)
Net deferred tax assets	$ 193.0	$ 181.5