Stock-Based Compensation Plans Deferred Stock Units (DSUs) (Details) - Director [Member] - Deferred Compensation, Share-based Payments - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Deferred Compensation Arrangement with Individual, Shares Outstanding	74,780	93,979
Deferred Compensation Arrangement with Individual, Shares granted	11,185
Deferred Compensation Arrangement with Individual, Shares Issued	(30,384)
Deferred Compensation Arrangement with Individual, Weighted Average Grant Date Fair Value Shares Vested	$ 54.85	$ 51.71
Deferred Compensation Arrangement with Individual, Weighted Average Grant Date Fair Value	78.33
Deferred Compensation Arrangement with Individual, Weighted Average Grant Date Fair Value of Shares Issued	$ 53.78
Deferred Compensation Arrangement with Individual, Compensation Expense	$ 0.9	$ 0.9	$ 1.0