Basis of Presentation and Principles of Consolidation (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Total other comprehensive (loss) income, net of tax	$ (48.7)		$ 17.7	$ (175.0)	$ 44.1
Comprehensive income (loss)	$ 50.6		$ 96.1	(8.0)	$ 167.7
Accounting Standards Update 2016-01 and 2018-02 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Total other comprehensive (loss) income, net of tax		$ (228.0)		(175.0)
Comprehensive income (loss)		(160.3)		$ (8.0)
Adoption of Accounting Standards Update		$ 101.7