Investments Investments - Mortgage loans amortized cost by debt service coverage ratio distribution and year of origination (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Debt and Equity Securities, FV-NI [Line Items]
Mortgage loans, net	$ 4,759	$ 4,817
Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	4,844	4,820
Allowance	(85)	(3)
Mortgage loans, net	4,759	4,817
Below 1.0 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	47	56
1.0 - 1.25 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	233	225
1.26 - 1.50 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	1,202	1,237
Above 1.50 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	3,362	$ 3,302
2015 and prior | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	2,032
2015 and prior | Below 1.0 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	15
2015 and prior | 1.0 - 1.25 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	66
2015 and prior | 1.26 - 1.50 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	535
2015 and prior | Above 1.50 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	1,416
2016 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	550
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	14
2016 | 1.26 - 1.50 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	14
2016 | Above 1.50 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	522
2017 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	554
2017 | Below 1.0 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	32
2017 | 1.0 - 1.25 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	32
2017 | 1.26 - 1.50 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	97
2017 | Above 1.50 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	393
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	0
2018 | 1.26 - 1.50 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	318
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	884
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	91
2019 | 1.26 - 1.50 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	238
2019 | Above 1.50 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	555
Current | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	137
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	0
Current | Above 1.50 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	$ 107