Investments - Mortgage Loans Credit Ratings Indicator (Details) - Commercial Real Estate - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	$ 1,164	$ 1,213
Category 1
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	56	58
Category 2 to 4
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	1,086	1,143
Categories 5 and 6
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	13	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	5	5
2020 | Category 1
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	0	0
2020 | Category 2 to 4
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	5	5
2020 | Categories 5 and 6
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	0	0
2020 | Category 7
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	0	0
2019
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	94	88
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	94	88
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	96	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	95	93
2018 | Categories 5 and 6
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	1	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	188	221
2017 | Category 1
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	15	15
2017 | Category 2 to 4
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	164	206
2017 | Categories 5 and 6
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	0	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	139	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	139	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	642	666
Prior | Category 1
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	41	43
Prior | Category 2 to 4
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	589	611
Prior | Categories 5 and 6
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	12	12
Prior | Category 7
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	$ 0	$ 0