Investments (excluding Consolidated Investment Entities) - Loans by U.S. Region (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Open Option Contracts Written [Line Items]
Total Commercial mortgage loans	$ 8,689	$ 8,006
Percentage of Total	99.99079%	100.00%
Pacific
Open Option Contracts Written [Line Items]
Total Commercial mortgage loans	$ 2,024	$ 2,055
Percentage of Total	23.40%	25.70%
South Atlantic
Open Option Contracts Written [Line Items]
Total Commercial mortgage loans	$ 1,716	$ 1,703
Percentage of Total	19.70%	21.30%
Middle Atlantic
Open Option Contracts Written [Line Items]
Total Commercial mortgage loans	$ 1,612	$ 1,169
Percentage of Total	18.50%	14.60%
West South Central
Open Option Contracts Written [Line Items]
Total Commercial mortgage loans	$ 959	$ 801
Percentage of Total	11.00%	10.00%
Mountain
Open Option Contracts Written [Line Items]
Total Commercial mortgage loans	$ 859	$ 729
Percentage of Total	9.90%	9.10%
East North Central
Open Option Contracts Written [Line Items]
Total Commercial mortgage loans	$ 884	$ 885
Percentage of Total	10.20%	11.10%
New England
Open Option Contracts Written [Line Items]
Total Commercial mortgage loans	$ 161	$ 170
Percentage of Total	1.80%	2.10%
West North Central
Open Option Contracts Written [Line Items]
Total Commercial mortgage loans	$ 391	$ 371
Percentage of Total	4.50%	4.60%
East South Central
Open Option Contracts Written [Line Items]
Total Commercial mortgage loans	$ 83	$ 123
Percentage of Total	1.00%	1.50%