Investments - Loans by Property Type (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Investment Holdings [Line Items]
Commercial mortgage loans	$ 4,664	$ 4,919
% of Total	100.00%	100.00%
Retail
Investment Holdings [Line Items]
Commercial mortgage loans	$ 1,198	$ 1,335
% of Total	25.70%	27.20%
Industrial
Investment Holdings [Line Items]
Commercial mortgage loans	$ 1,216	$ 1,323
% of Total	26.20%	26.90%
Apartments
Investment Holdings [Line Items]
Commercial mortgage loans	$ 1,185	$ 1,104
% of Total	25.40%	22.40%
Office
Investment Holdings [Line Items]
Commercial mortgage loans	$ 697	$ 791
% of Total	14.90%	16.10%
Hotel/Motel
Investment Holdings [Line Items]
Commercial mortgage loans	$ 127	$ 111
% of Total	2.70%	2.30%
Mixed Use
Investment Holdings [Line Items]
Commercial mortgage loans	$ 44	$ 46
% of Total	0.90%	0.90%
Other
Investment Holdings [Line Items]
Commercial mortgage loans	$ 197	$ 209
% of Total	4.20%	4.20%