Shareholders' Equity (Summary of Share Repurchases) (Details) - USD ($) $ / shares in Units, $ in Millions		1 Months Ended	3 Months Ended		9 Months Ended
	Jan. 02, 2020	Nov. 05, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Total number of shares purchased (in millions)	13,870		600,000	700,000	1,400,000	1,200,000
Average price paid per share			$ 302.63	$ 249.04	$ 267.57	$ 231.20
Total price paid (in millions)	$ 3.3		$ 175.6	$ 175.7	$ 375.6	$ 270.3
Subsequent Event [Member]
Total number of shares purchased (in millions)		0.4
Average price paid per share		$ 299.54
Total price paid (in millions)		$ 124.4