Investments (Summary of the Companies Voting Control in Entities Where it has Noncontrolling Interest) (Details) - Germany	Dec. 31, 2020
VV Immobilien Verwaltungs und Beteiligungs GmbH
Segment Reporting Information [Line Items]
% Voting Interest Owned (percent)	70.00%
HVH Immobilien und Beteiligungs GmbH
Segment Reporting Information [Line Items]
% Voting Interest Owned (percent)	70.00%

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