Significant Accounting Policies Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2018

Accounting Policies [Abstract]

New Accounting Pronouncements and Changes in Accounting Principles

Based on our review of our performance obligations in our contracts with customers, we changed the consolidated statement of operations classification for certain transactions from revenue to cost of sales or from cost of sales to revenue. For theyear ended December 31, 2018, the reclassification of revenues and cost of sales resulted in a net decrease in revenue of approximately$671.0 million or 8.0%, compared to total revenues based on accounting prior to the adoption of ASC 606, with an equivalent net decrease in cost of sales. The change in total revenues as a result of the adoption of ASC 606 is made up of the following revenue line item changes (in millions):

	Increase (Decrease) in Revenue Due to ASC 606 Adoption
	Year Ended December 31, 2018
Product sales	$	(235	)
Product sales—related parties	(52		)
Midstream services	(357		)
Midstream services—related parties	(27		)
Total	$	(671	)

Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction

The following table summarizes the expected impact to our consolidated statements of operations, resulting from either revenue or reductions to cost of sales, from MVC and firm transportation contractual provisions. All amounts in the table below reflect 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. In addition, amounts in the table below 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.

2019	$	252.1
2020	247.9
2021	104.5
2022	95.0
2023	92.9
Thereafter	281.9
Total	$	1,074.3

Property, Plant and Equipment

The components of property and equipment are as follows (in millions):

	Year Ended December 31,
	2018			2017
Transmission assets	$	1,329.4		$	1,338.7
Gathering systems	4,410.5			4,040.9
Gas processing plants	3,590.5			3,401.8
Other property and equipment	171.7			157.8
Construction in process	312.0			180.8
Property and equipment	9,814.1			9,120.0
Accumulated depreciation	(2,967.4		)	(2,533.0		)
Property and equipment, net of accumulated depreciation	$	6,846.7		$	6,587.0

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 - 15 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 gross operating 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,
	2018		2017		2016
Devon	10.4	%	14.4	%	18.5	%
Dow Hydrocarbons and Resources LLC	11.1	%	11.2	%	10.8	%
Marathon Petroleum Corporation	11.5	%	(1)		(1)

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(1) Consolidated revenues for Marathon Petroleum Corporation did not exceed 10% of our consolidated revenues for the years endedDecember 31, 2017and2016