Derivative Instruments and Hedging Activities (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($)
Derivative [Line Items]
Unrealized Gain (Loss) on Price Risk Cash Flow Derivatives, before Tax	$ (9.9)
Derivative Instruments, Gain (Loss) Reclassification from Accumulated OCI to Income, Estimated Net Amount to be Transferred	$ 8.5