Subsequent Events (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended													12 Months Ended
	Jan. 24, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Feb. 19, 2019
Subsequent Event [Line Items]
Distributions per Limited Partner unit (in dollars per share)		$ 0.40000	$ 0.38200	$ 0.36500	$ 0.34800	$ 0.33300	$ 0.31800	$ 0.30410	$ 0.29100	$ 0.27700	$ 0.26375	$ 0.25000	$ 0.23500	$ 0.22000	$ 1.4950	$ 1.2461	$ 1.0258
Subsequent Event
Subsequent Event [Line Items]
Distributions per Limited Partner unit (in dollars per share)	$ 0.4000
Subsequent Event | Shell Pipeline Company L P | General Partner
Subsequent Event [Line Items]
Administrative fee payable																		$ 10.5