Summary of Significant Accounting Policies - New Accounting Pronouncement (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jan. 01, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase in revenues		$ 11,170.0	$ 10,207.0	$ 10,360.0
Accounting Standards Update 2016-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Tax benefit		$ 24.8
Forecast | Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase in revenues	$ 225.0
Subsequent Event | Accounting Standards Update 2016-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Available-for-sale equity securities reclassified					$ 443.0
Equity securities held at fair value					$ 443.0