Stock-Based Compensation (Changes in Stock Appreciation Rights) (Details) - Stock Appreciation Rights [Member] $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized | $	$ 9.6
Shares (2)
Outstanding awards as of beginning of period (in shares) | shares	1.1
Granted (in shares) | shares	0.2
Exercised (in shares) | shares	(0.2)
Forfeited (in shares) | shares	0.0
Outstanding awards as of end of period (in shares) | shares	1.1
Exercisable at end of period (in shares) | shares	0.7
Weighted-Average Exercise Price per Share
Outstanding awards as of beginning of period (in usd per share) | $ / shares	$ 98.35
Granted (in usd per share) | $ / shares	205.53
Exercised (in usd per share) | $ / shares	70.00
Forfeited (in usd per share) | $ / shares	0.00
Outstanding as of end of period (in shares) | $ / shares	121.63
Exercisable at end of period, Weighted-Average Exercise Price per Share (in usd per share) | $ / shares	$ 90.43