Summary of Significant Accounting Policies (Pro Forma Information For New Accounting Standard) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue	$ 2,560.0	$ 2,562.0	$ 2,526.7	$ 2,392.8	$ 2,379.1	$ 2,409.3	$ 2,350.7	$ 2,248.6	$ 10,041.5	$ 9,387.7	$ 9,115.0
Operating Income (Loss)	$ 406.8	$ 448.1	$ 425.5	$ 388.1	$ 392.0	$ 417.9	$ 382.1	$ 345.5	1,668.5	$ 1,537.5	$ 1,558.8
Pro Forma
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue									9,646.2
Operating Income (Loss)									1,668.5
Accounting Standards Update 2014-09 | Pro Forma
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue									(395.3)
Operating Income (Loss)									$ 0.0