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Summary of Significant Accounting Policies (Details 2) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Change in Accounting Estimate [Line Items] |  |  |
Approximate amount by which basis of assets and liabilities for tax reporting purposes is lower than amount reported on consolidated balance sheet | $ 47 |  |
Common Shares [Member] |  |  |
Change in Accounting Estimate [Line Items] |  |  |
Ordinary income (as a percent) | 83.10% | 86.50% | 48.00%
Return of capital (as a percent) | 16.90% | 13.50% | 52.00%
Preferred Shares [Member] |  |  |
Change in Accounting Estimate [Line Items] |  |  |
Ordinary income (as a percent) |  | 100.00% | 100.00%
Return of capital (as a percent) |  | 0.00% | 0.00%

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