Repurchases of Common Stock (Stock Repurchase Program 2013 - 2015) (Details) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended			36 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2015
Accelerated Share Repurchases [Line Items]
Number of shares repurchased (in shares)		2,514,139	7,925,227	3,306,433	13,745,799
Average price per share (in usd per share)		$ 63.56	$ 68.31	$ 58.98	$ 65.20
Repurchases of common stock		$ 159,800	$ 545,140	$ 195,004	$ 896,175
Repurchases of common stock, excluding fees and expenses			$ 541,371
Open Market Share Repurchase
Accelerated Share Repurchases [Line Items]
Number of shares repurchased (in shares)			2,633,526
Average price per share (in usd per share)			$ 64.77
Repurchases of common stock			$ 170,582
Tender Offer
Accelerated Share Repurchases [Line Items]
Number of shares repurchased (in shares)	[1]		5,291,701
Average price per share (in usd per share)	[1]		$ 70.07
Repurchases of common stock	[1]		$ 370,789

[1] Fees and expenses totaling $3.7 million associated with the tender offer do not impact the repurchase program approved by our Board, are excluded from the total purchase price shown here and were recorded as part of the cost of treasury stock in our Consolidated Balance Sheets.