v3.26.1
Significant Accounting Policies - Derivative Financial Instruments (Details)
€ in Millions, $ in Millions
3 Months Ended
Mar. 31, 2026
USD ($)
€ / shares
Y
DerivativeInstrument
Mar. 31, 2025
USD ($)
Mar. 31, 2026
EUR (€)
€ / shares
Y
DerivativeInstrument
Dec. 31, 2025
USD ($)
Y
€ / shares
DerivativeInstrument
Dec. 31, 2025
EUR (€)
Y
€ / shares
DerivativeInstrument
Derivative Financial Instruments          
Number of credit-risk-related hedging or derivative activities | DerivativeInstrument 0   0    
Unamortized gain on treasury locks and terminated hedges $ 33.6     $ 35.3  
Amount expected to be reclassified from accumulated other comprehensive loss to earnings within the next year 6.6        
Gains (losses) of cumulative translation adjustment (35.7) $ 78.1      
Gross accumulated other comprehensive income (loss) related to derivative activities 33.1     25.0  
Exchange traded option | Option pricing model          
Derivative Financial Instruments          
Forward contract net, fair value 125.4     205.1  
Simon Property Group, L.P          
Derivative Financial Instruments          
Gross accumulated other comprehensive income (loss) related to derivative activities $ 38.9     $ 29.3  
Klepierre | Exchange traded option | Option pricing model | Stock price          
Derivative Financial Instruments          
Derivative liability measurement input | € / shares 32.58   32.58 33.74 33.74
Klepierre | Exchange traded option | Option pricing model | Implied volatility          
Derivative Financial Instruments          
Derivative liability measurement input 0.1692   0.1692 0.1778 0.1778
Klepierre | Exchange traded option | Option pricing model | EUR risk-free rate          
Derivative Financial Instruments          
Derivative liability measurement input 0.0237   0.0237 0.0204 0.0204
Klepierre | Exchange traded option | Option pricing model | Expected dividend yield          
Derivative Financial Instruments          
Derivative liability measurement input 0.0523   0.0523 0.0506 0.0506
Klepierre | Exchange traded option | Option pricing model | Expected term          
Derivative Financial Instruments          
Derivative liability measurement input | Y 0.62   0.62 0.87 0.87
Klepierre | Exchange traded option | Option pricing model | Credit Spread          
Derivative Financial Instruments          
Derivative liability measurement input 0.0033   0.0033 0.0045 0.0045
Interest rate swap | Deferred costs and other assets          
Derivative Financial Instruments          
Interest rate derivative assets, fair value $ 2.4     $ 1.5  
Interest rate swap | Other liabilities          
Derivative Financial Instruments          
Interest rate derivative liabilities, fair value $ 6.8     $ 12.8  
US denominated interest rate swap          
Derivative Financial Instruments          
Number of Instruments | DerivativeInstrument 13   13 7 7
Notional Amount $ 2,800.0     $ 2,200.0  
Euro denominated interest rate swap          
Derivative Financial Instruments          
Number of Instruments | DerivativeInstrument 2   2 3 3
Notional Amount | €     € 190.4   € 541.7
US denominated interest rate cap          
Derivative Financial Instruments          
Number of Instruments | DerivativeInstrument 1   1 1 1
Notional Amount $ 85.0     $ 85.0  
Euro denominated interest rate cap          
Derivative Financial Instruments          
Number of Instruments | DerivativeInstrument 3   3 3 3
Notional Amount | €     € 178.8   € 178.8
USD-Euro currency forward contract | January 15 2026 | Net Investment Hedging | Designated as Hedging Instrument          
Derivative Financial Instruments          
Notional Amount | €         125.0
Forward contract net, fair value       $ 0.3  
USD-Euro currency forward contract | January 15 2026 | Net Investment Hedging | Designated as Hedging Instrument          
Derivative Financial Instruments          
Notional Amount | €         125.0
Forward contract net, fair value       0.3  
USD-Euro currency forward contract | February 18, 2026 | Net Investment Hedging | Designated as Hedging Instrument          
Derivative Financial Instruments          
Notional Amount | €         50.5
Forward contract net, fair value       (0.4)  
USD-Euro currency forward contract | March 16 2026 | Net Investment Hedging | Designated as Hedging Instrument          
Derivative Financial Instruments          
Notional Amount | €         50.0
Forward contract net, fair value       0.1  
USD-Euro currency forward contract | May 15, 2026 | Net Investment Hedging | Designated as Hedging Instrument          
Derivative Financial Instruments          
Notional Amount | €     50.0   50.0
Forward contract net, fair value $ 1.2     0.1  
USD-Euro currency forward contract | May 15, 2026 | Net Investment Hedging | Designated as Hedging Instrument          
Derivative Financial Instruments          
Notional Amount | €     125.0    
Forward contract net, fair value 1.8        
USD-Euro currency forward contract | June 17, 2026 | Net Investment Hedging | Designated as Hedging Instrument          
Derivative Financial Instruments          
Notional Amount | €     50.0    
Forward contract net, fair value (0.1)        
USD-Euro currency forward contract | June 17, 2026 | Net Investment Hedging | Designated as Hedging Instrument          
Derivative Financial Instruments          
Notional Amount | €     50.5    
Forward contract net, fair value 1.7        
USD-Euro currency forward contract | June 17, 2026 | Net Investment Hedging | Designated as Hedging Instrument          
Derivative Financial Instruments          
Notional Amount | €     50.0    
Forward contract net, fair value (0.1)        
USD-Euro currency forward contract | July 15, 2026 | Net Investment Hedging | Designated as Hedging Instrument          
Derivative Financial Instruments          
Notional Amount | €     50.0   50.0
Forward contract net, fair value 1.2     0.1  
USD-Euro currency forward contract | July 15, 2026 | Net Investment Hedging | Designated as Hedging Instrument          
Derivative Financial Instruments          
Notional Amount | €     75.0    
Forward contract net, fair value (0.2)        
USD-Euro currency forward contract | July 15, 2026 | Net Investment Hedging | Designated as Hedging Instrument          
Derivative Financial Instruments          
Notional Amount | €     15.0    
Forward contract net, fair value 0.1        
USD-Euro currency forward contract | January 15, 2027 | Net Investment Hedging | Designated as Hedging Instrument          
Derivative Financial Instruments          
Notional Amount | €     € 100.0   € 100.0
Forward contract net, fair value $ 2.5     $ 0.3