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Summary of Significant Accounting Policies - Summary of Impacts of Revisions to the Risk-Free Discount Rate Applied to Environmental Remediation Liabilities and Recovery Assets (Detail) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Accounting Policies [Abstract] |  |  |
Charge (reduction) to operating expenses | $ (2) | $ (2) | $ 10
Risk-free discount rate applied to environmental remediation liabilities and recovery assets | 2.50% | 2.25% | 2.00%

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- Definition Rate applied to the undiscounted amount of environmental loss contingencies to arrive at the present value recorded as of the balance sheet date. + References Reference 1: 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 2: 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 + Details
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- Definition The increase (decrease) to operating expense due to changes in discount rates used to estimate present value of environmental remediation obligations and recovery assets. + References No definition available. + Details
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