Earnings Per Share (Narrative) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	2 Months Ended	12 Months Ended		98 Months Ended
	Feb. 27, 2019	Dec. 31, 2018	Dec. 31, 2017	Feb. 27, 2019
Earnings Per Share
Common stock repurchased, shares		6,061	9,301
Common stock repurchased, average price per share		$ 282.80	$ 233.57
Common stock repurchased, value		$ 1,713,953	$ 2,172,437
Subsequent event [Member]
Earnings Per Share
Common stock repurchased, shares	800			73,100
Common stock repurchased, average price per share	$ 342.95			$ 150.73
Common stock repurchased, value	$ 268,900			$ 11,000,000