Earnings Per Share (Narrative) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	2 Months Ended	12 Months Ended		110 Months Ended
	Feb. 28, 2020	Dec. 31, 2019	Dec. 31, 2018	Feb. 28, 2020
Earnings Per Share
Common stock repurchased, shares		3,877	6,061
Common stock repurchased, average price per share		$ 369.55	$ 282.80
Common stock repurchased, value		$ 1,432,752	$ 1,713,953
Subsequent event [Member]
Earnings Per Share
Common stock repurchased, shares	900			77,100
Common stock repurchased, average price per share	$ 400.78			$ 162.72
Common stock repurchased, value	$ 363,400			$ 12,500,000