Commitments and Contingencies Contingencies (Details) $ in Millions	3 Months Ended
Sep. 30, 2017 USD ($)
Accounts Payable and Accrued Liabilities [Member] \| Operating Expense [Member] \| Tioga, North Dakota Crude Oil Pipeline Release [Member] \| Judicial Ruling [Member] \| Unfavorable Regulatory Action [Member]
Loss Contingencies [Line Items]
Loss Contingency Accrual, Period Increase (Decrease)	$ 19

Amount of increase (decrease) in loss contingency liability.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14326-108349

Name:	us-gaap_LossContingencyAccrualCarryingValuePeriodIncreaseDecrease
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration