Investments - Mortgage Loans Credit Ratings Indicator (Details) - Commercial Real Estate - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	$ 1,124	$ 1,213
Category 1
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	62	58
Category 2 to 4
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	1,016	1,143
Categories 5 and 6
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	37	12
Category 7
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	9	0
2020
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	57
2020 | Category 1
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	0
2020 | Category 2 to 4
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	57
2020 | Categories 5 and 6
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	0
2020 | Category 7
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	0
2019
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	95	93
2019 | Category 1
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	0	0
2019 | Category 2 to 4
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	95	93
2019 | Categories 5 and 6
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	0	0
2019 | Category 7
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	0	0
2018
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	94	93
2018 | Category 1
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	0	0
2018 | Category 2 to 4
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	90	93
2018 | Categories 5 and 6
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	4	0
2018 | Category 7
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	0	0
2017
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	165	221
2017 | Category 1
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	23	15
2017 | Category 2 to 4
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	129	206
2017 | Categories 5 and 6
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	4	0
2017 | Category 7
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	9	0
2016
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	129	140
2016 | Category 1
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	0	0
2016 | Category 2 to 4
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	129	140
2016 | Categories 5 and 6
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	0	0
2016 | Category 7
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	0	0
Prior
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	584	666
Prior | Category 1
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	39	43
Prior | Category 2 to 4
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	516	611
Prior | Categories 5 and 6
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	29	12
Prior | Category 7
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	$ 0	$ 0