Derivative Financial Instruments and Risk Management Policies - Sensitivity Analysis Due to Fluctuations in Interest Rates (Details) € in Millions	12 Months Ended
Dec. 31, 2017 EUR (€)
Change in interest rate
Increase in interest rate	1.00%
Decrease in interest rate	(1.00%)
Impact on consolidated income statement
Decrease in consolidated income	€ (91)
Increase in consolidated income	74
Impact on consolidated equity
Increase in consolidated equity	335
Decrease in consolidated equity	€ (331)

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Sensitivity Analysis, Impact On Equity Due To Changes In Interest Rate [Abstract]

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