Quarterly report pursuant to Section 13 or 15(d)

Unsecured Lines of Credit Payable - Schedule of Credit Unused and Available (Details)

v3.8.0.1
Unsecured Lines of Credit Payable - Schedule of Credit Unused and Available (Details) - USD ($)
Mar. 31, 2018
Dec. 31, 2017
Line of Credit Facility [Line Items]    
Borrowings outstanding $ (260,000,000) $ (166,000,000)
Credit facility 2018 [Member]    
Line of Credit Facility [Line Items]    
Committed capacity 1,500,000,000.0  
Line of Credit | Credit facility 2018 [Member]    
Line of Credit Facility [Line Items]    
Committed capacity 700,000,000.0  
Borrowings outstanding (260,000,000) $ (166,000,000)
Unused and available $ 440,000,000