Significant Accounting Policies Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2020

Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction

The following table summarizes the contractually committed fees that we expect to recognize in our consolidated statements of operations, in either revenue or reductions to cost of sales, from MVC and firm transportation contractual provisions. All amounts in the table below are determined using the contractually-stated MVC or firm transportation volumes specified for each period multiplied by the relevant deficiency or reservation fee. Actual amounts could differ due to the timing of revenue recognition or reductions to cost of sales resulting from make-up right provisions included in our agreements, as well as due to nonpayment or nonperformance by our customers. These fees do not represent the shortfall amounts we expect to collect under our MVC contracts, as we generally do not expect volume shortfalls to equal the full amount of the contractual MVCs during these periods. For example, for the year ended December 31, 2020, we had contractual commitments of $174.3 million under our MVC contracts and recorded $57.2 million of revenue due to volume shortfalls.


MVC and Firm Transportation Commitments (in millions) (1)
2021	$	121.1
2022	102.4
2023	91.5
2024	77.4
2025	34.8
Thereafter	110.1
Total	$	537.3

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(1)Amounts do not represent expected shortfall under these commitments.

Property, Plant and Equipment

The components of property and equipment, net of accumulated depreciation are as follows (in millions):


	Year Ended December 31,
	2020		2019
Transmission assets	$	1,410.5	$	1,376.5
Gathering systems	4,782.9		4,856.5
Gas processing plants	4,082.1		3,862.2
Other property and equipment	161.0		188.0
Construction in process	78.6		216.7
Property and equipment	10,515.1		10,499.9
Accumulated depreciation	(3,863.0)		(3,418.6)
Property and equipment, net of accumulated depreciation	$	6,652.1	$	7,081.3

Depreciation Expense. Depreciation is calculated using the straight-line method based on the estimated useful life of each asset, as follows:


			Useful Lives
Transmission assets			20 - 25 years
Gathering systems			20 - 25 years
Gas processing plants			20 - 25 years
Other property and equipment			3 - 25 years

Schedules of Concentration of Risk, by Risk Factor

The following customers individually represented greater than 10% of our consolidated revenues. These customers represent a significant percentage of revenues, and the loss of the customer would have a material adverse impact on our results of operations because the revenues and adjusted gross margin received from transactions with these customers is material to us. No other customers represented greater than 10% of our consolidated revenues.


	Year Ended December 31,
	2020		2019		2018
Devon	14.4	%	10.5	%	10.4	%
Dow Hydrocarbons and Resources LLC	13.2	%	10.0	%	11.1	%
Marathon Petroleum Corporation	12.2	%	13.8	%	11.5	%