Stock Repurchase (Shares Repurchased) (Details) - $ / shares	1 Months Ended												12 Months Ended
	Dec. 31, 2016	Nov. 30, 2016	Oct. 31, 2016	Sep. 30, 2016	Aug. 31, 2016	Jul. 31, 2016	Jun. 30, 2016	May 31, 2016	Apr. 30, 2016	Mar. 31, 2016	Feb. 29, 2016	Jan. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Class of Stock Disclosures [Abstract]
Number of Shares Purchased	481,600	539,943	1,065,648	1,028,006	1,177,372	485,725	439,031	845,869	1,033,098	1,405,025	869,898	1,147,337	10,518,552	4,184,889	3,298,490
Average Price Paid Per Share (in USD per share)	$ 91.38	$ 83.79	$ 86.96	$ 89.92	$ 85.92	$ 86.61	$ 84.75	$ 87.01	$ 79.90	$ 76.12	$ 70.69	$ 78.44	$ 82.65
Total Number of Shares Purchased as Part of Publicly Announced Programs	481,600	539,943	1,065,648	1,028,006	1,177,372	485,725	439,031	845,869	1,033,098	1,405,025	869,898	1,147,337	10,518,552