Investments - Loans by Property Type (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Investment Holdings [Line Items]
Gross Carrying Value	$ 4,682	$ 4,919
% of Total	100.00%	100.00%
Retail
Investment Holdings [Line Items]
Gross Carrying Value	$ 1,211	$ 1,335
% of Total	25.90%	27.20%
Industrial
Investment Holdings [Line Items]
Gross Carrying Value	$ 1,278	$ 1,323
% of Total	27.20%	26.90%
Apartments
Investment Holdings [Line Items]
Gross Carrying Value	$ 1,142	$ 1,104
% of Total	24.40%	22.40%
Office
Investment Holdings [Line Items]
Gross Carrying Value	$ 684	$ 791
% of Total	14.60%	16.10%
Hotel/Motel
Investment Holdings [Line Items]
Gross Carrying Value	$ 122	$ 111
% of Total	2.60%	2.30%
Mixed Use
Investment Holdings [Line Items]
Gross Carrying Value	$ 45	$ 46
% of Total	1.00%	0.90%
Other
Investment Holdings [Line Items]
Gross Carrying Value	$ 200	$ 209
% of Total	4.30%	4.20%