Investments - Mortgage Loans Credit Ratings Indicator (Details) - Commercial Real Estate - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Mortgage Loans on Real Estate [Line Items]
Mortgage loans	$ 934	$ 1,047
Category 1
Mortgage Loans on Real Estate [Line Items]
Mortgage loans	51	59
Category 2 to 4
Mortgage Loans on Real Estate [Line Items]
Mortgage loans	870	952
Categories 5 and 6
Mortgage Loans on Real Estate [Line Items]
Mortgage loans	13	36
Category 7
Mortgage Loans on Real Estate [Line Items]
Mortgage loans	0	0
2021
Mortgage Loans on Real Estate [Line Items]
Mortgage loans	171
2021 | Category 1
Mortgage Loans on Real Estate [Line Items]
Mortgage loans	0
2021 | Category 2 to 4
Mortgage Loans on Real Estate [Line Items]
Mortgage loans	171
2021 | Categories 5 and 6
Mortgage Loans on Real Estate [Line Items]
Mortgage loans	0
2021 | Category 7
Mortgage Loans on Real Estate [Line Items]
Mortgage loans	0
2020
Mortgage Loans on Real Estate [Line Items]
Mortgage loans	44	46
2020 | Category 1
Mortgage Loans on Real Estate [Line Items]
Mortgage loans	0	0
2020 | Category 2 to 4
Mortgage Loans on Real Estate [Line Items]
Mortgage loans	44	46
2020 | Categories 5 and 6
Mortgage Loans on Real Estate [Line Items]
Mortgage loans	0	0
2020 | Category 7
Mortgage Loans on Real Estate [Line Items]
Mortgage loans	0	0
2019
Mortgage Loans on Real Estate [Line Items]
Mortgage loans	64	96
2019 | Category 1
Mortgage Loans on Real Estate [Line Items]
Mortgage loans	0	0
2019 | Category 2 to 4
Mortgage Loans on Real Estate [Line Items]
Mortgage loans	64	96
2019 | Categories 5 and 6
Mortgage Loans on Real Estate [Line Items]
Mortgage loans	0	0
2019 | Category 7
Mortgage Loans on Real Estate [Line Items]
Mortgage loans	0	0
2018
Mortgage Loans on Real Estate [Line Items]
Mortgage loans	76	94
2018 | Category 1
Mortgage Loans on Real Estate [Line Items]
Mortgage loans	0	0
2018 | Category 2 to 4
Mortgage Loans on Real Estate [Line Items]
Mortgage loans	73	91
2018 | Categories 5 and 6
Mortgage Loans on Real Estate [Line Items]
Mortgage loans	3	3
2018 | Category 7
Mortgage Loans on Real Estate [Line Items]
Mortgage loans	0	0
2017
Mortgage Loans on Real Estate [Line Items]
Mortgage loans	101	150
2017 | Category 1
Mortgage Loans on Real Estate [Line Items]
Mortgage loans	22	22
2017 | Category 2 to 4
Mortgage Loans on Real Estate [Line Items]
Mortgage loans	75	124
2017 | Categories 5 and 6
Mortgage Loans on Real Estate [Line Items]
Mortgage loans	4	4
2017 | Category 7
Mortgage Loans on Real Estate [Line Items]
Mortgage loans	0	0
Prior
Mortgage Loans on Real Estate [Line Items]
Mortgage loans	478	661
Prior | Category 1
Mortgage Loans on Real Estate [Line Items]
Mortgage loans	29	37
Prior | Category 2 to 4
Mortgage Loans on Real Estate [Line Items]
Mortgage loans	443	595
Prior | Categories 5 and 6
Mortgage Loans on Real Estate [Line Items]
Mortgage loans	6	29
Prior | Category 7
Mortgage Loans on Real Estate [Line Items]
Mortgage loans	$ 0	$ 0