Subsequent Events (Details) - USD ($)		12 Months Ended
	Feb. 05, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Feb. 14, 2018
Subsequent Event [Line Items]
Dividends declared per share (in dollars per share)		$ 1.88	$ 1.73	$ 1.67
Subsequent Event
Subsequent Event [Line Items]
Dividends declared per share (in dollars per share)	$ 0.47
Stock repurchase program, authorized amount					$ 200,000,000