Investments - Mortgage Loans Credit Ratings Indicator (Details) - Commercial Real Estate - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	$ 1,290	$ 1,361
Category 1
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	44	42
Category 2 to 4
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	1,234	1,301
Categories 5 and 6
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	12	18
Category 7
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Mortgage loans	$ 0	$ 0