Equity-Based Compensation - Stock Options and Stock Appreciation Rights (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Shares
End of Period (in shares)	0
Stock Options and SARs
Shares
Beginning of Period (in shares)	955,000	1,206,000
Exercised (in shares)	(595,000)	(227,000)
Forfeited or Expired (in shares)	(360,000)	(24,000)
End of Period (in shares)	0	955,000
Weighted-Average Exercise Price
Beginning of Period (in USD per share)	$ 77.52	$ 76.29
Exercised (in USD per share)	81.71	70.59
Forfeited or Expired (in USD per share)	70.59	81.71
End of Period (in USD per share)	$ 0.00	$ 77.52
Weighted average contractual term of options outstanding	0 days
Total Intrinsic Value	$ 0.0