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Summary of Significant Accounting Policies - Goodwill Identified by Segment (Parenthetical) (Detail) $ in Millions | Dec. 31, 2017 USD ($)
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Goodwill and Intangible Assets Disclosure [Abstract] |
Accumulated goodwill impairment | $ 2,457

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- Definition Amount of accumulated impairment loss for an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a,h) -URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267 + Details
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