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Income Taxes - Schedule of Changes in Valuation Allowance (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Valuation Allowance [Line Items] |  |  |
Balance at beginning of year | $ 2,584 | $ 1,940 | $ 1,291
Increase to allowance | 136 | 831 | 772
Release of allowance | (154) | (246) | (209)
Acquisitions and divestitures (F) | 0 | (1) | (1)
Tax apportionment, tax rate and tax law changes | (14) | (24) | 106
Foreign currency translation | (66) | 84 | (19)
Balance at end of year | 2,486 | $ 2,584 | $ 1,940
Other Net State Deferred Tax Asset |  |  |
Valuation Allowance [Line Items] |  |  |
Balance at end of year | $ 675 |  |

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- Definition Deferred tax assets valuation acquisitions divestitures. + References No definition available. + Details
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- Definition Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32537-109319 + Details
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- Definition Amount of increase (decrease) in the valuation allowance for a specified deferred tax asset. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 45 -Paragraph 20 -URI http://asc.fasb.org/extlink&oid=84176650&loc=d3e32123-109318 + Details
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