Investments - Mortgage loans (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($) loan item	Dec. 31, 2018 USD ($)
Mortgage Loans on Real Estate
Mortgage loans	$ 3,988	$ 3,995
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	35.60%	33.50%
Office buildings
Mortgage Loans on Real Estate
Percentage of mortgage portfolio carrying value	22.40%	23.90%
Warehouse
Mortgage Loans on Real Estate
Percentage of mortgage portfolio carrying value	16.20%	15.90%
Retail
Mortgage Loans on Real Estate
Percentage of mortgage portfolio carrying value	14.30%	15.00%
Other
Mortgage Loans on Real Estate
Percentage of mortgage portfolio carrying value	11.50%	11.70%
Texas
Mortgage Loans on Real Estate
Percentage of mortgage portfolio carrying value	16.80%	15.60%
California
Mortgage Loans on Real Estate
Percentage of mortgage portfolio carrying value	14.10%	15.20%
Illinois
Mortgage Loans on Real Estate
Percentage of mortgage portfolio carrying value	8.00%	8.50%
Florida
Mortgage Loans on Real Estate
Percentage of mortgage portfolio carrying value	6.70%	6.40%
New Jersey
Mortgage Loans on Real Estate
Percentage of mortgage portfolio carrying value	6.00%	7.20%
Mortgage loans, not in foreclosure
Mortgage Loans on Real Estate
Mortgage loans	$ 3,988
Percentage of mortgage portfolio carrying value	100.00%
Number of loans | item	264
Mortgage loans, not in foreclosure | 2019
Mortgage Loans on Real Estate
Mortgage loans	$ 52
Percentage of mortgage portfolio carrying value	1.30%
Number of loans | loan	9
Mortgage loans, not in foreclosure | 2020
Mortgage Loans on Real Estate
Mortgage loans	$ 371
Percentage of mortgage portfolio carrying value	9.30%
Number of loans | loan	35
Mortgage loans, not in foreclosure | 2021
Mortgage Loans on Real Estate
Mortgage loans	$ 336
Percentage of mortgage portfolio carrying value	8.40%
Number of loans | loan	24
Mortgage loans, not in foreclosure | 2022
Mortgage Loans on Real Estate
Mortgage loans	$ 684
Percentage of mortgage portfolio carrying value	17.20%
Number of loans | loan	49
Mortgage loans, not in foreclosure | Thereafter
Mortgage Loans on Real Estate
Mortgage loans	$ 2,545
Percentage of mortgage portfolio carrying value	63.80%
Number of loans | loan	147