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Revenue from Contracts with Customers - Contract Assets Rollforward (Details) - USD ($) $ in Millions | 3 Months Ended
--- | ---
Mar. 31, 2019 | Mar. 31, 2018
Capitalized Cost To Fulfill Customer Contracts |  |
Change in Capitalized Contract Costs |  |
Balance at beginning of period | $ 329 | $ 298
Additions | 346 | 1,504
Amortization | (439) | (1,465)
Impairment | 0 | 0
Foreign currency and other | 0 | (8)
Balance at end of period | 236 | 329
Capitalized Cost To Obtain Customer Contracts |  |
Change in Capitalized Contract Costs |  |
Balance at beginning of period | 156 | 145
Additions | 9 | 53
Amortization | (11) | (41)
Impairment | 0 | 0
Foreign currency and other | 1 | (1)
Balance at end of period | $ 155 | $ 156

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- Definition Amount of amortization expense for asset recognized from cost incurred to obtain or fulfill contract with customer. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 340 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=68051541&loc=SL49131252-203054 + Details
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- Definition Amount of impairment loss for asset recognized from cost incurred to obtain or fulfill contract with customer. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 340 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=68051541&loc=SL49131252-203054 + Details
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- Definition Amount, after accumulated amortization and accumulated impairment loss, of asset recognized from cost incurred to obtain or fulfill contract with customer. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 340 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=68051541&loc=SL49131252-203054 + Details
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