Investments - Loans by U.S. Region (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Open Option Contracts Written [Line Items]
Gross Carrying Value	$ 4,682	$ 4,919
% of Total	100.00%	100.00%
Pacific
Open Option Contracts Written [Line Items]
Gross Carrying Value	$ 995	$ 994
% of Total	21.30%	20.20%
South Atlantic
Open Option Contracts Written [Line Items]
Gross Carrying Value	$ 930	$ 1,011
% of Total	19.90%	20.50%
Middle Atlantic
Open Option Contracts Written [Line Items]
Gross Carrying Value	$ 1,014	$ 1,039
% of Total	21.60%	21.20%
West South Central
Open Option Contracts Written [Line Items]
Gross Carrying Value	$ 507	$ 566
% of Total	10.80%	11.50%
Mountain
Open Option Contracts Written [Line Items]
Gross Carrying Value	$ 471	$ 458
% of Total	10.10%	9.30%
East North Central
Open Option Contracts Written [Line Items]
Gross Carrying Value	$ 393	$ 465
% of Total	8.40%	9.50%
New England
Open Option Contracts Written [Line Items]
Gross Carrying Value	$ 84	$ 75
% of Total	1.80%	1.50%
West North Central
Open Option Contracts Written [Line Items]
Gross Carrying Value	$ 222	$ 258
% of Total	4.70%	5.20%
East South Central
Open Option Contracts Written [Line Items]
Gross Carrying Value	$ 66	$ 53
% of Total	1.40%	1.10%