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Environmental matters (Details 2) - USD ($) | 3 Months Ended |
--- | --- | ---
Mar. 31, 2017 | Jan. 06, 2017
Portland Harbor Site [Member] |  |
Site Contingency [Line Items] |  |
Environmental matters investigative costs | $ 100,000,000 |
Environmental matters, estimated costs |  | $ 1,000,000,000
Eugene, OR Manufactured Gas Plant Site [Member] |  |
Site Contingency [Line Items] |  |
Estimated proportional share of cleanup liability | 50.00% |
Accrual for environmental loss contingencies | $ 1,600,000 |
Bremerton, WA Manufactured Gas Plant Site [Member] |  |
Site Contingency [Line Items] |  |
Accrual for environmental loss contingencies | 12,400,000 |
Bellingham, WA Manufactured Gas Plant Site [Member] |  |
Site Contingency [Line Items] |  |
Site contingency, loss exposure not accrued, best estimate | 8,000,000 |
Minimum [Member] | Eugene, OR Manufactured Gas Plant Site [Member] |  |
Site Contingency [Line Items] |  |
Site contingency, loss exposure not accrued, best estimate | 500,000 |
Minimum [Member] | Bremerton, WA Manufactured Gas Plant Site [Member] |  |
Site Contingency [Line Items] |  |
Site contingency, loss exposure not accrued, best estimate | 340,000 |
Maximum [Member] | Eugene, OR Manufactured Gas Plant Site [Member] |  |
Site Contingency [Line Items] |  |
Site contingency, loss exposure not accrued, best estimate | 11,000,000 |
Maximum [Member] | Bremerton, WA Manufactured Gas Plant Site [Member] |  |
Site Contingency [Line Items] |  |
Site contingency, loss exposure not accrued, best estimate | $ 6,400,000 |

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- Definition Total costs accrued as of the balance sheet date for environmental loss contingencies. + References 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 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 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 25 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6395460&loc=d3e13647-108346 + Details
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