Incentive Plan (Weighted Average Fair Value of Incentive Award) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Long-term incentive units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average fair value (in dollars per share)	$ 101.86	$ 109.71	$ 87.18
Restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average fair value (in dollars per share)	100.33	108.65	83.58
Market performance-based awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average fair value (in dollars per share)	$ 119.29	$ 111.06	$ 82.90