Commitments and Contingencies (Standby Letters of Credit) (Details) - Revolving Credit Facility - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Loss Contingencies [Line Items]
Letters of credit outstanding amount		$ 35.1
Letter of Credit Availability	$ 359.4	295.7
Debt Disclosure [Abstract]
Senior secured revolving credit facility	600.0	900.0
Maximum
Debt Disclosure [Abstract]
Letter of credit sublimit	$ 300.0	$ 600.0
Letter of credit sublimit percentage	90.00%	90.00%