Concentrations of Risk - Schedule of diversification of the Account's portfolio by region and property type (Details)	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Concentration Risk [Line Items]
Concentration risk percentage	100.00%	100.00%
Office
Concentration Risk [Line Items]
Concentration risk percentage	38.20%
Apartment
Concentration Risk [Line Items]
Concentration risk percentage	24.70%
Retail
Concentration Risk [Line Items]
Concentration risk percentage	19.00%
Industrial
Concentration Risk [Line Items]
Concentration risk percentage	14.90%
Other
Concentration Risk [Line Items]
Concentration risk percentage	3.20%
West
Concentration Risk [Line Items]
Concentration risk percentage	40.00%
West | Office
Concentration Risk [Line Items]
Concentration risk percentage	14.60%
West | Apartment
Concentration Risk [Line Items]
Concentration risk percentage	9.40%
West | Retail
Concentration Risk [Line Items]
Concentration risk percentage	7.10%
West | Industrial
Concentration Risk [Line Items]
Concentration risk percentage	8.40%
West | Other
Concentration Risk [Line Items]
Concentration risk percentage	0.50%
East
Concentration Risk [Line Items]
Concentration risk percentage	32.50%
East | Office
Concentration Risk [Line Items]
Concentration risk percentage	18.40%
East | Apartment
Concentration Risk [Line Items]
Concentration risk percentage	7.20%
East | Retail
Concentration Risk [Line Items]
Concentration risk percentage	3.00%
East | Industrial
Concentration Risk [Line Items]
Concentration risk percentage	1.40%
East | Other
Concentration Risk [Line Items]
Concentration risk percentage	2.50%
South
Concentration Risk [Line Items]
Concentration risk percentage	25.20%
South | Office
Concentration Risk [Line Items]
Concentration risk percentage	5.20%
South | Apartment
Concentration Risk [Line Items]
Concentration risk percentage	7.20%
South | Retail
Concentration Risk [Line Items]
Concentration risk percentage	8.00%
South | Industrial
Concentration Risk [Line Items]
Concentration risk percentage	4.60%
South | Other
Concentration Risk [Line Items]
Concentration risk percentage	0.20%
Midwest
Concentration Risk [Line Items]
Concentration risk percentage	2.30%
Midwest | Office
Concentration Risk [Line Items]
Concentration risk percentage	0.00%
Midwest | Apartment
Concentration Risk [Line Items]
Concentration risk percentage	0.90%
Midwest | Retail
Concentration Risk [Line Items]
Concentration risk percentage	0.90%
Midwest | Industrial
Concentration Risk [Line Items]
Concentration risk percentage	0.50%
Midwest | Other
Concentration Risk [Line Items]
Concentration risk percentage	0.00%