Fair Value Measurements (Unobservable Quantitative Input Ratios) (Details)	Dec. 31, 2020	Dec. 31, 2019
Discount rates
Unobservable Quantitative Input
Real estate, measurement input	0.070
Discount rates | Level 3 | Recurring | Maximum | Loans Receivable
Unobservable Quantitative Input
Loans receivable, measurement input	0.065
Discount rates | Level 3 | Recurring | Weighted Average | Loans Receivable
Unobservable Quantitative Input
Loans receivable, measurement input	0.065
Discount rates | Level 3 | Recurring | Real estate fund investments | Minimum
Unobservable Quantitative Input
Real estate, measurement input	0.076	0.086
Discount rates | Level 3 | Recurring | Real estate fund investments | Maximum
Unobservable Quantitative Input
Real estate, measurement input	0.150	0.120
Discount rates | Level 3 | Recurring | Real estate fund investments | Weighted Average
Unobservable Quantitative Input
Real estate, measurement input	0.127	0.099
Terminal capitalization rates | Level 3 | Recurring | Loans Receivable
Unobservable Quantitative Input
Loans receivable, measurement input	0.050
Terminal capitalization rates | Level 3 | Recurring | Weighted Average | Loans Receivable
Unobservable Quantitative Input
Loans receivable, measurement input	0.050
Terminal capitalization rates | Level 3 | Recurring | Real estate fund investments | Minimum
Unobservable Quantitative Input
Real estate, measurement input	0.055	0.049
Terminal capitalization rates | Level 3 | Recurring | Real estate fund investments | Maximum
Unobservable Quantitative Input
Real estate, measurement input	0.103	0.082
Terminal capitalization rates | Level 3 | Recurring | Real estate fund investments | Weighted Average
Unobservable Quantitative Input
Real estate, measurement input	0.079	0.059