Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies (Details 4)

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Summary of Significant Accounting Policies (Details 4) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Income Tax Disclosure [Line Items]      
Approximate amount by which basis of assets and liabilities for tax reporting purposes is higher (lower) than amount reported on consolidated balance sheet $ 52    
Common Shares      
Income Tax Disclosure [Line Items]      
Ordinary income (as a percent) 54.40% 83.10% 86.50%
Return of capital (as a percent) 45.60% 16.90% 13.50%
Preferred Shares      
Income Tax Disclosure [Line Items]      
Ordinary income (as a percent)     100.00%
Return of capital (as a percent)     0.00%