Investments Investments - Mortgage loans amortized cost by debt service coverage ratio distribution and year of origination (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Debt and Equity Securities, FV-NI [Line Items]
Mortgage loans, net	$ 4,774	$ 4,817
Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	4,860	4,820
Allowance	(86)	(3)
Mortgage loans, net	4,774	4,817
Below 1.0 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	71	56
1.0 - 1.25 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	365	225
1.26 - 1.50 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	1,260	1,237
Above 1.50 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	3,164	$ 3,302
2015 and prior | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	2,001
2015 and prior | Below 1.0 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	38
2015 and prior | 1.0 - 1.25 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	170
2015 and prior | 1.26 - 1.50 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	494
2015 and prior | Above 1.50 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	1,299
2016 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	547
2016 | Below 1.0 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	0
2016 | 1.0 - 1.25 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	27
2016 | 1.26 - 1.50 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	27
2016 | Above 1.50 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	493
2017 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	553
2017 | Below 1.0 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	33
2017 | 1.0 - 1.25 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	36
2017 | 1.26 - 1.50 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	123
2017 | Above 1.50 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	361
2018 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	687
2018 | Below 1.0 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	0
2018 | 1.0 - 1.25 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	87
2018 | 1.26 - 1.50 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	231
2018 | Above 1.50 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	369
2019 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	883
2019 | Below 1.0 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	0
2019 | 1.0 - 1.25 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	15
2019 | 1.26 - 1.50 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	369
2019 | Above 1.50 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	499
Current | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	189
Current | Below 1.0 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	0
Current | 1.0 - 1.25 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	30
Current | 1.26 - 1.50 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	16
Current | Above 1.50 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	$ 143