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Financial Risk Management - Summary of Effect of Foreign Currency Derivatives Impacts and Commercial Transactions Exposures (Detail) - EUR (€) € in Millions | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |  |
Realized gains / (losses) on foreign currency derivatives - net | € 11 | € (15) | € (46)
Included in Unrealized (losses) / gains on foreign currency derivatives - net | (3) | 17 | 40
Derivatives that do not qualify for hedge accounting [member] | Other gains and losses [member] |  |  |
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |  |
Realized gains / (losses) on foreign currency derivatives - net | 9 | (19) | (46)
Included in Unrealized (losses) / gains on foreign currency derivatives - net | (1) | 16 | 40
Derivatives that qualify for hedge accounting [member] | Other gains and losses [member] |  |  |
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |  |
Realized gains / (losses) on foreign currency derivatives - net | (2) | 3 |
Realized gains / (losses) in ineffective portion of derivatives | 0 | 0 | 0
Derivatives that qualify for hedge accounting [member] | Revenue [member] |  |  |
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |  |
Realized gains / (losses) on foreign currency derivatives - net | 4 | 1 |
Included in Unrealized (losses) / gains on foreign currency derivatives - net | (2) | 1 |
Derivatives that qualify for hedge accounting [member] | Other comprehensive income (loss) [member] |  |  |
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |  |
Included in Unrealized (losses) / gains on foreign currency derivatives - net | (23) | 48 | € (27)
(Losses) reclassified from cash flow hedge reserve to Consolidated Income Statement | € (2) | € (2) |

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