Shareholders' Equity (Details) - USD ($)		3 Months Ended		9 Months Ended
	Jan. 03, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Business Acquisition Equity Interests Issued Or Issuable [Line Items]
Number of shares authorized to be repurchased		7,100,000		7,100,000
Purchase of treasury stock		$ 0	$ 18,300,000	$ 13,000,000	$ 113,500,000
Treasury Stock, Shares, Acquired			600,000	300,000	3,400,000
Treasury Stock Acquired, Average Cost Per Share			$ 30.52	$ 43.83	$ 33.22
Common stock reissued				1,900,000
City Securities [Member]
Business Acquisition Equity Interests Issued Or Issuable [Line Items]
Stock Issued During Period Shares Acquisitions	200,000