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Summary of Significant Accounting Policies - Recent Accounting Developments (Details) - USD ($) $ in Millions | 3 Months Ended
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Mar. 31, 2018 | Mar. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |
Cost of operations | $ 1,558 | $ 1,862
Other income/(expense), net | $ (3) | 13
ASU 2017-07 |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |
Cost of operations |  | 4
Other income/(expense), net |  | $ 4

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- Definition The aggregate cost of goods produced and sold and services rendered during the reporting period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.2) -URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688 + Details
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