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Derivatives, Hedges, Financial Instruments and Carbon Credits - Schedule of Carrying Values and Estimated Fair Values of Financial Instruments (Parenthetical) (Detail) - $ / shares | 9 Months Ended | 12 Months Ended
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Sep. 30, 2016 | Dec. 31, 2015
Derivative Instruments And Hedging Activities Disclosure [Abstract] |  |
Notes based on quoted price | $ 101.13 | $ 83.65

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- Definition Price at which a dealer is willing to buy an instrument, used as an input to measure fair value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (bbb) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
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