Investments - Mortgage loans (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($) loan	Dec. 31, 2018 USD ($)
Mortgage Loans on Real Estate
Carrying value	$ 4,817	$ 4,670
Percent	100.00%	100.00%
Mortgage loans, not in foreclosure
Mortgage Loans on Real Estate
Number of loans | loan	286
Carrying value	$ 4,817
Percent	100.00%
Mortgage loans, not in foreclosure | 2020
Mortgage Loans on Real Estate
Number of loans | loan	9
Carrying value	$ 58
Percent	1.20%
Mortgage loans, not in foreclosure | 2021
Mortgage Loans on Real Estate
Number of loans | loan	36
Carrying value	$ 446
Percent	9.30%
Mortgage loans, not in foreclosure | 2022
Mortgage Loans on Real Estate
Number of loans | loan	28
Carrying value	$ 460
Percent	9.50%
Mortgage loans, not in foreclosure | 2023
Mortgage Loans on Real Estate
Number of loans | loan	52
Carrying value	$ 776
Percent	16.10%
Mortgage loans, not in foreclosure | Thereafter
Mortgage Loans on Real Estate
Number of loans | loan	161
Carrying value	$ 3,077
Percent	63.90%
Apartment complex
Mortgage Loans on Real Estate
Percent	36.80%	34.40%
Office buildings
Mortgage Loans on Real Estate
Percent	22.60%	24.50%
Warehouse
Mortgage Loans on Real Estate
Percent	16.80%	15.80%
Retail
Mortgage Loans on Real Estate
Percent	13.40%	14.40%
Other
Mortgage Loans on Real Estate
Percent	10.40%	10.90%
Texas
Mortgage Loans on Real Estate
Percent	16.90%	14.90%
California
Mortgage Loans on Real Estate
Percent	15.10%	16.40%
Illinois
Mortgage Loans on Real Estate
Percent	7.10%	7.80%
Florida
Mortgage Loans on Real Estate
Percent	6.40%	6.10%
New Jersey
Mortgage Loans on Real Estate
Percent	5.60%	6.80%
North Carolina
Mortgage Loans on Real Estate
Percent	4.50%	5.10%