Investments - Market value of investments listed in regulated stock markets (Details) - EUR (€) € / shares in Units, € in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Investments
Net carrying amount	€ 9,035	€ 7,044	€ 3,511
Joint ventures
Investments
Net carrying amount	€ 4,592	€ 5,497
Joint ventures \| Saipem SpA
Investments
Number of shares held	308,767,968
% of the investment	30.99%	30.99%
Share price	€ 4.356
Market value	€ 1,345
Net carrying amount	€ 1,250	€ 1,228

The amount of investments accounted for using the equity method. The equity method is a method of accounting whereby the investment is initially recognised at cost and adjusted thereafter for the post-acquisition change in the investor's share of net assets of the investee. The investor's profit or loss includes its share of the profit or loss of the investee. The investor's other comprehensive income includes its share of the other comprehensive income of the investee. [Refer: At cost [member]]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
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-IssueDate 2019-01-01
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
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-IssueDate 2019-01-01
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-Subparagraph e
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