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Capital and financial risk management - Risk management strategy of hedge relationships - Additional information (Details) - EUR (€)
€ in Millions
12 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Fair value hedges    
Risk management strategy of hedge relationships    
Loss from foreign currency basis outside the cash flow and net investment hedge relationships € 1,164 € 1,271
Gain from foreign currency basis outside the cash flow and net investment hedge relationships 0  
Net ineffectiveness on the fair value hedges, recognised in the income statement 8 8
Loss in relation to fair value of bonds previously designated in fair value hedge relationships 774 889
Cash flow hedges    
Risk management strategy of hedge relationships    
Hedge ineffectiveness of swaps 0 0
Net investment hedge    
Risk management strategy of hedge relationships    
Hedge ineffectiveness of swaps 0 0
Interest rate risk | Fair value hedges    
Risk management strategy of hedge relationships    
Cumulative fair value adjustment for the hedged interest rate risk € 76 € 85