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Financial Risk Management - Summary of Effect of Foreign Currency Derivatives Impacts and Financing Transaction Exposures (Detail) - EUR (€) € in Millions | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |  |
Realized gain / (loss) on foreign currency derivatives-net | € (15) | € (46) | € (37)
Unrealized gain / (loss) on foreign currency derivatives-net | 17 | 40 | (10)
Total | (79) | 45 | € 50
Currency risk [member] | Finance costs [member] |  |  |
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |  |
Realized gain / (loss) on foreign currency derivatives-net | 31 | 15 |
Unrealized gain / (loss) on foreign currency derivatives-net | (110) | 30 |
Total | € (79) | € 45 |

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- Definition Unrealized gains (losses) on foreign currency derivatives - net. + References No definition available. + Details
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