Commitments and Contingencies, Guarantees and Indemnifications (Details) - USD ($)	Mar. 31, 2018	Dec. 31, 2017
Guarantees [Abstract]
Assets held as collateral	$ 0	$ 0
Payment or Performance Guarantee
Guarantees [Abstract]
Guarantees issued and outstanding	18,600,000	18,800,000
Current exposure under these guarantees	0	0
Payment or Performance Guarantee \| Surety Bonds
Guarantees [Abstract]
Guarantees issued and outstanding	51,700,000	53,100,000
Other MGP Sites [Member]
Guarantees [Abstract]
Accrual for Environmental Loss Contingencies, Gross	$ 4,000,000	$ 4,000,000

Undiscounted amount of the accrual for environmental loss contingencies.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 5.Y.Q1)
-URI http://asc.fasb.org/extlink&oid=27011672&loc=d3e149879-122751

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 30
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13207-110859

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=82913245&loc=d3e12069-110248

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- References

No definition available.

+ Details

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- Definition

The amount of assets held either as collateral or by third parties that, upon the occurrence of any triggering event or condition under the guarantee, the guarantor can obtain and liquidate to recover all or a portion of the amounts paid under the guarantee.

+ References

No definition available.

+ Details

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- Definition

Current estimate of exposure under the guarantee or each group of similar guarantees before reduction for potential recoveries.

+ References

No definition available.

+ Details

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- Details

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- Details

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- Details

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