Stock Repurchases, Dividends and Earnings per Share - Share Repurchase Activity (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Equity [Abstract]
Number of shares repurchased (in shares)	1.1	3.3	2.6	7.1
Amount paid	$ 91.0	$ 219.5	$ 202.5	$ 474.0
Weighted average cost per share (in dollars per share)	$ 82.63	$ 67.47	$ 78.11	$ 67.05