Investments - Mortgage loans amortized cost by debt service coverage ratio distribution and year of origination (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Debt and Equity Securities, FV-NI [Line Items]
Mortgage loans, net	$ 752	$ 746
Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	759	754
Allowance	(7)	(8)
Mortgage loans, net	752	746
Mortgage loans | 2016 and prior
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	120
Mortgage loans | 2017
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	45
Mortgage loans | 2018
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	146
Mortgage loans | 2019
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	279
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	92
Below 1.0 | Mortgage loans
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	0	0
Below 1.0 | Mortgage loans | 2016 and prior
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	0
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	46	46
1.0 - 1.25 | Mortgage loans | 2016 and prior
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	11
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	25
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	153	201
1.26 - 1.50 | Mortgage loans | 2016 and prior
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	43
1.26 - 1.50 | Mortgage loans | 2017
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	5
1.26 - 1.50 | Mortgage loans | 2018
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	0
1.26 - 1.50 | Mortgage loans | 2019
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	105
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	560	$ 507
Above 1.50 | Mortgage loans | 2016 and prior
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	66
Above 1.50 | Mortgage loans | 2017
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	40
Above 1.50 | Mortgage loans | 2018
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	146
Above 1.50 | Mortgage loans | 2019
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	149
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	$ 92