Summary of Significant Accounting Policies (Statement of Cash flows) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash used in investing activities	$ (1,229.1)	$ (1,330.2)	$ (964.5)
Cash and cash equivalents	70.5	83.3	67.8
Restricted cash and marketable securities	108.1	141.1	90.5
Less: restricted marketable securities	(45.3)	(45.3)	(45.3)
Cash, cash equivalents, restricted cash and restricted cash equivalents	$ 133.3	179.1	113.0	$ 86.5
Accounting Standards Update 2016-18
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash used in investing activities		$ 50.6	$ (8.9)