Derivative Financial Instruments and Risk Management Policies - Derivatives Policy (Details) - EUR (€) € in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Financial Instruments [Abstract]
Nominal value of outstanding derivatives	€ 145,166	€ 152,096
Decrease in outstanding derivatives	4.60%
Interest rate risk \| Cash flow hedges
Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [line items]
Average interest rate (as a percent)	4.00%
Interest rate risk \| Cash flow hedges \| Minimum
Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [line items]
Average interest rate (as a percent)	2.00%
Interest rate risk \| Cash flow hedges \| Maximum
Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [line items]
Average interest rate (as a percent)	4.00%

The average rate of a hedging instrument. [Refer: Hedging instruments [member]]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Note Effective 2018-01-01
-Name IFRS
-Number 7
-IssueDate 2017-01-01
-Paragraph 23B
-Subparagraph b
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2017-03-01&anchor=para_23B_b&doctype=Standard
-URIDate 2017-03-09

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- Definition

Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes of the table.

+ References

No definition available.

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- Definition

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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- Definition

Financial Instruments [Abstract]

+ References

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- Definition

Percentage Increase (Decrease) In Outstanding Derivatives

+ References

No definition available.

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