Note 2 - Acquisitions Acquisitions (Details) - USD ($) $ in Millions							3 Months Ended	9 Months Ended	12 Months Ended
	Aug. 06, 2018	May 01, 2018	Nov. 08, 2017	Nov. 21, 2016	Sep. 16, 2016	Jul. 01, 2016	Sep. 30, 2018	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	[1]
Business Acquisition [Line Items]
Borrowings under revolving credit agreement									$ 1,320	$ 1,225	$ 1,451
Payments to Acquire Businesses, Gross								$ 300	$ 300	$ 406	$ 760
Business Acquisition, Equity Interest Issued or Issuable, Value Assigned							$ 1,250	$ 1,250
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares							28,283,742
Logistics Assets Drop Down and Asset Transfer [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred	$ 1,550
Wamsutter Pipeline System [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross		$ 180
Alaska Logistics Assets [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred						$ 444
Anacortes Logistics Assets [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred			$ 445
Borrowings under revolving credit agreement			400
Business Combination, Consideration Transferred, Equity Interests Issued and Issuable			$ 45
Martinez Logistics Assets [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred				$ 400
Payments to Acquire Businesses, Gross				360
Business Acquisition, Equity Interest Issued or Issuable, Value Assigned				$ 40
Martinez Logistics Assets [Member] | Common
Business Acquisition [Line Items]
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares				860,933
Martinez Logistics Assets [Member] | General Partner
Business Acquisition [Line Items]
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares				17,570
Alaska Logistics Assets [Member] | Phase One
Business Acquisition [Line Items]
Business Combination, Consideration Transferred						266
Payments to Acquire Businesses, Gross						240
Business Acquisition, Equity Interest Issued or Issuable, Value Assigned						$ 26
Alaska Logistics Assets [Member] | Phase Two
Business Acquisition [Line Items]
Business Combination, Consideration Transferred					$ 178
Payments to Acquire Businesses, Gross					160
Business Acquisition, Equity Interest Issued or Issuable, Value Assigned					$ 18
Alaska Logistics Assets [Member] | Common | Phase One
Business Acquisition [Line Items]
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares						390,282
Alaska Logistics Assets [Member] | Common | Phase Two
Business Acquisition [Line Items]
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares					358,712
Alaska Logistics Assets [Member] | General Partner | Phase One
Business Acquisition [Line Items]
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares						162,375
Alaska Logistics Assets [Member] | General Partner | Phase Two
Business Acquisition [Line Items]
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares					20,440
Rangeland RIO Pipeline, LLC [Member]
Business Acquisition [Line Items]
Equity Method Investment, Ownership Percentage									67.00%

[1] All periods include the historical results of the Predecessors. See Notes 1 and 2 for further discussion.