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Subsequent Events (Details) - Joint Ventures with Northwestern Mutual
$ in Millions
Nov. 02, 2018
USD ($)
Sep. 30, 2018
property
Schedule of Equity Method Investments [Line Items]    
Number of real estate properties | property   233
Northwestern Mutual Joint Venture | Corporate Joint Venture | Subsequent Event    
Schedule of Equity Method Investments [Line Items]    
Number of real estate properties 17  
Equity Method Investment, Summarized Financial Information, Assets $ 368  
Equity Method Investment Third Party Ownership Percentage 85.00%  
Equity method Investment, ownership percentage 15.00%  
Equity Method Investment, Summarized Financial Information, Noncurrent Liabilities $ 175