Basis of Presentation (Details) - shares shares in Millions	Oct. 27, 2017	Sep. 30, 2017	Sep. 30, 2016
Percent of General Partner Interest Owned by Holding Company (in hundredths)		2.00%	2.00%
Subsequent Event
Number of the Partnership's common units owned by holding company (in units)	125.6
Percent of General Partner Interest Owned by Holding Company (in hundredths)	2.00%
Percentage of Partnership's Equity Interests Owned by Holding Company (in hundredths)	51.00%