Units Outstanding (Details) - shares	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Units Outstanding
Outstanding as of December 31, 2017 (in units)	268,659,333
Options exercised (in units)	629,493	1,000,000
Units issued (in units)	2,712,263
Units retired (in units)	(3,435,327)
Balance as of September 30, 2018 (in units)	268,565,762
Limited Partners' Capital Account [Line Items]
Units purchased and retired (in units)	3,435,327
AB Units
Units Outstanding
Units retired (in units)	(4,546)
Limited Partners' Capital Account [Line Items]
Units purchased and retired (in units)	4,546