Investments - Loans by U.S. Region (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Open Option Contracts Written [Line Items]
Loans by property type percentage of total loans	100.00%	100.00%
Loans by region percentage of total loans	100.00%	100.00%
Total Commercial mortgage loans	$ 4,919	$ 4,911
Pacific
Open Option Contracts Written [Line Items]
Loans by region percentage of total loans	20.20%	20.10%
Total Commercial mortgage loans	$ 994	$ 985
South Atlantic
Open Option Contracts Written [Line Items]
Loans by region percentage of total loans	20.50%	20.00%
Total Commercial mortgage loans	$ 1,011	$ 982
Middle Atlantic
Open Option Contracts Written [Line Items]
Loans by region percentage of total loans	21.20%	22.40%
Total Commercial mortgage loans	$ 1,039	$ 1,097
East North Central
Open Option Contracts Written [Line Items]
Loans by region percentage of total loans	9.50%	9.50%
Total Commercial mortgage loans	$ 465	$ 468
West South Central
Open Option Contracts Written [Line Items]
Loans by region percentage of total loans	11.50%	11.20%
Total Commercial mortgage loans	$ 566	$ 552
Mountain
Open Option Contracts Written [Line Items]
Loans by region percentage of total loans	9.30%	9.30%
Total Commercial mortgage loans	$ 458	$ 457
New England
Open Option Contracts Written [Line Items]
Loans by region percentage of total loans	1.50%	1.60%
Total Commercial mortgage loans	$ 75	$ 77
West North Central
Open Option Contracts Written [Line Items]
Loans by region percentage of total loans	5.20%	4.90%
Total Commercial mortgage loans	$ 258	$ 243
East South Central
Open Option Contracts Written [Line Items]
Loans by region percentage of total loans	1.10%	1.00%
Total Commercial mortgage loans	$ 53	$ 50