Investments (Details 12) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($) item loan	Dec. 31, 2015 USD ($)
Mortgage Loans on Real Estate
Mortgage loans	$ 3,938	$ 3,781
Threshold percentage of mortgage loans to total carrying value	5.00%
Percentage of mortgage portfolio carrying value	100.00%	100.00%
Apartment complex
Mortgage Loans on Real Estate
Percentage of mortgage portfolio carrying value	26.40%	24.50%
Office buildings
Mortgage Loans on Real Estate
Percentage of mortgage portfolio carrying value	24.30%	23.20%
Retail
Mortgage Loans on Real Estate
Percentage of mortgage portfolio carrying value	21.40%	22.40%
Warehouse
Mortgage Loans on Real Estate
Percentage of mortgage portfolio carrying value	16.50%	18.10%
Other
Mortgage Loans on Real Estate
Percentage of mortgage portfolio carrying value	11.40%	11.80%
California
Mortgage Loans on Real Estate
Percentage of mortgage portfolio carrying value	19.30%	21.60%
Texas
Mortgage Loans on Real Estate
Percentage of mortgage portfolio carrying value	11.00%	9.50%
New Jersey
Mortgage Loans on Real Estate
Percentage of mortgage portfolio carrying value	8.50%	9.10%
Illinois
Mortgage Loans on Real Estate
Percentage of mortgage portfolio carrying value	7.40%	8.00%
Florida
Mortgage Loans on Real Estate
Percentage of mortgage portfolio carrying value	6.00%	5.90%
New York
Mortgage Loans on Real Estate
Percentage of mortgage portfolio carrying value	3.80%	5.00%
Mortgage loans, not in foreclosure
Mortgage Loans on Real Estate
Mortgage loans	$ 3,938
Percentage of mortgage portfolio carrying value	100.00%
Number of loans | item	278
Mortgage loans, not in foreclosure | 2017
Mortgage Loans on Real Estate
Mortgage loans	$ 288
Percentage of mortgage portfolio carrying value	7.30%
Number of loans | loan	27
Mortgage loans, not in foreclosure | 2018
Mortgage Loans on Real Estate
Mortgage loans	$ 252
Percentage of mortgage portfolio carrying value	6.40%
Number of loans | loan	24
Mortgage loans, not in foreclosure | 2019
Mortgage Loans on Real Estate
Mortgage loans	$ 200
Percentage of mortgage portfolio carrying value	5.10%
Number of loans | loan	7
Mortgage loans, not in foreclosure | 2020
Mortgage Loans on Real Estate
Mortgage loans	$ 180
Percentage of mortgage portfolio carrying value	4.60%
Number of loans | loan	14
Mortgage loans, not in foreclosure | Thereafter
Mortgage Loans on Real Estate
Mortgage loans	$ 3,018
Percentage of mortgage portfolio carrying value	76.60%
Number of loans | loan	206