Segments and Related Information (Significant Customers) (Narrative) (Details) - Revenue Benchmark - Customer Concentration Risk	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Enbridge, Inc.
Segments and Related Information [Line Items]
Concentration risk, percentage of total	12.00%	1.00%	18.00%	1.00%
AT&T
Segments and Related Information [Line Items]
Concentration risk, percentage of total	12.00%	19.00%	12.00%	21.00%
Permian Highway Pipeline
Segments and Related Information [Line Items]
Concentration risk, percentage of total	0.00%	10.00%	0.00%	7.00%