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Revenue from Contracts with Customers - Contract Assets Rollforward (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2021 | Sep. 30, 2020
Capitalized Cost To Fulfill Customer Contracts |  |  |  |
Change in Capitalized Contract Costs |  |  |  |
Balance at beginning of period | $ 222 | $ 193 | $ 339 | $ 335
Additions | 340 | 291 | 1,022 | 883
Amortization | (310) | (266) | (1,110) | (995)
Impairment | 0 | 0 | 0 | 0
Foreign currency translation and other | (3) | 2 | (2) | (3)
Balance at end of period | 249 | 220 | 249 | 220
Capitalized Cost To Obtain Customer Contracts |  |  |  |
Change in Capitalized Contract Costs |  |  |  |
Balance at beginning of period | 175 | 172 | 184 | 171
Additions | 12 | 15 | 40 | 43
Amortization | (11) | (12) | (36) | (35)
Impairment | 0 | 0 | 0 | 0
Foreign currency translation and other | (2) | 1 | (14) | (3)
Balance at end of period | $ 174 | $ 176 | $ 174 | $ 176

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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://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 340 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=123353750&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://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 340 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=123353750&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://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 340 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=123353750&loc=SL49131252-203054 + Details
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