Investments - Loans by Property Type (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Investment Holdings [Line Items]
Gross Carrying Value	$ 4,741	$ 4,919
% of Total	100.00%	100.00%
Retail
Investment Holdings [Line Items]
Gross Carrying Value	$ 1,304	$ 1,335
% of Total	27.60%	27.20%
Industrial
Investment Holdings [Line Items]
Gross Carrying Value	$ 1,282	$ 1,323
% of Total	27.10%	26.90%
Apartments
Investment Holdings [Line Items]
Gross Carrying Value	$ 1,072	$ 1,104
% of Total	22.60%	22.40%
Office
Investment Holdings [Line Items]
Gross Carrying Value	$ 707	$ 791
% of Total	14.90%	16.10%
Hotel/Motel
Investment Holdings [Line Items]
Gross Carrying Value	$ 125	$ 111
% of Total	2.60%	2.30%
Mixed Use
Investment Holdings [Line Items]
Gross Carrying Value	$ 45	$ 46
% of Total	0.90%	0.90%
Other
Investment Holdings [Line Items]
Gross Carrying Value	$ 206	$ 209
% of Total	4.30%	4.20%