Investments - Mortgage loans amortized cost by debt service coverage ratio distribution and year of origination (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Debt and Equity Securities, FV-NI [Line Items]
Mortgage loans, net	$ 786	$ 746
Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	793	754
Allowance	(7)	(8)
Mortgage loans, net	786	746
Mortgage loans | 2016 and prior
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	187
Mortgage loans | 2017
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	54
Mortgage loans | 2018
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	156
Mortgage loans | 2019
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	319
Mortgage loans | 2020
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	77
Mortgage loans | Current
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	0
Below 1.0 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	9	0
Below 1.0 | Mortgage loans | 2016 and prior
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	9
Below 1.0 | Mortgage loans | 2017
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	0
Below 1.0 | Mortgage loans | 2018
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	0
Below 1.0 | Mortgage loans | 2019
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	0
Below 1.0 | Mortgage loans | 2020
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	0
Below 1.0 | Mortgage loans | Current
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	0
1.0 - 1.25 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	53	46
1.0 - 1.25 | Mortgage loans | 2016 and prior
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	29
1.0 - 1.25 | Mortgage loans | 2017
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	0
1.0 - 1.25 | Mortgage loans | 2018
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	0
1.0 - 1.25 | Mortgage loans | 2019
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	14
1.0 - 1.25 | Mortgage loans | 2020
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	10
1.0 - 1.25 | Mortgage loans | Current
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	0
1.26 - 1.50 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	204	201
1.26 - 1.50 | Mortgage loans | 2016 and prior
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	31
1.26 - 1.50 | Mortgage loans | 2017
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	10
1.26 - 1.50 | Mortgage loans | 2018
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	29
1.26 - 1.50 | Mortgage loans | 2019
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	134
1.26 - 1.50 | Mortgage loans | 2020
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	0
1.26 - 1.50 | Mortgage loans | Current
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	0
Above 1.50 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	527	$ 507
Above 1.50 | Mortgage loans | 2016 and prior
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	118
Above 1.50 | Mortgage loans | 2017
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	44
Above 1.50 | Mortgage loans | 2018
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	127
Above 1.50 | Mortgage loans | 2019
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	171
Above 1.50 | Mortgage loans | 2020
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	67
Above 1.50 | Mortgage loans | Current
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	$ 0