Stock-Based Compensation (Stock Option Activity) (Details) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) $ / shares shares
Number of Options
Options outstanding beginning of the year (in shares) | shares	171,517
Exercised (in shares) | shares	(65,523)
Options outstanding end of the year (in shares) | shares	105,994
Weighted Average Exercise Price
Options outstanding beginning of the year (in dollars per share) | $ / shares	$ 41.59
Exercised (in dollars per share) | $ / shares	39.37
Options outstanding end of the year (in dollars per share) | $ / shares	$ 42.95
Options outstanding, Aggregate Intrinsic Value | $	$ 7