Earnings Per Share (Narrative) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	2 Months Ended	12 Months Ended		74 Months Ended
	Feb. 28, 2017	Dec. 31, 2016	Dec. 31, 2015	Feb. 28, 2017
Earnings Per Share
Common stock repurchased, shares		5,698	4,901
Common stock repurchased, average price per share		$ 264.21	$ 231.81
Common stock repurchased, value		$ 1,505,371	$ 1,136,139
Subsequent event [Member]
Earnings Per Share
Common stock repurchased, shares	1,400			58,400
Common stock repurchased, average price per share	$ 267.32			$ 124.14
Common stock repurchased, value	$ 387,500			$ 7,200,000