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Income Taxes - Reconciliation of Unrecognized Tax Benefits (Excluding Interest and Penalties) (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Income Tax Disclosure [Abstract] |  |  |
Balance at beginning of year | $ 73 | $ 28 | $ 18
Additions for tax positions of the current year | 0 | 23 | 12
Additions for tax positions of prior years | 143 | 27 | 0
Reductions for tax positions of prior years | (42) | 0 | 0
Settlements with tax authorities | 0 | 0 | (1)
Expiration of the statute of limitations | (6) | (5) | (1)
Foreign currency translation | (2) | 0 | 0
Balance at end of year | $ 166 | $ 73 | $ 28

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- Definition Amount of unrecognized tax benefits. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 45 -Paragraph 10B -URI http://asc.fasb.org/extlink&oid=84176650&loc=SL37586934-109318 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=84230637&loc=SL6600010-109319 + Details
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- Definition Amount of increase in unrecognized tax benefits resulting from tax positions that have been or will be taken in current period tax return. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=84230637&loc=SL6600010-109319 + Details
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