Earnings Per Share (Narrative) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended		82 Months Ended
	Nov. 07, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Nov. 07, 2017
Earnings Per Share
Common stock repurchased, shares		2,743	367	8,047	3,673
Common stock repurchased, average price per share		$ 200.70	$ 281.04	$ 235.26	$ 261.32
Common stock repurchased, value		$ 550,530	$ 102,941	$ 1,893,068	$ 959,743
Subsequent event [Member]
Earnings Per Share
Common stock repurchased, shares	400					65,400
Common stock repurchased, average price per share	$ 209.61					$ 135.17
Common stock repurchased, value	$ 85,200					$ 8,800,000