Members' Equity - Components to Compute Basic and Diluted Earnings per Unit (Details) - shares shares in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Basic weighted average units outstanding:
Weighted average common units outstanding (in shares)	181.1	180.5	179.7
Diluted weighted average units outstanding:
Weighted average basic common units outstanding (in shares)	181.1	180.5	179.7
Dilutive effect of restricted units issued (in shares)	0.0	1.3	0.0
Total weighted average diluted common units outstanding (in shares)	181.1	181.8	179.7