Investments - Mortgage loans amortized cost by debt service coverage ratio distribution and year of origination (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Debt and Equity Securities, FV-NI [Line Items]
Mortgage loans, net	$ 4,075	$ 4,817
Mortgage loans on real estate
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	4,142	4,820
Allowance	(67)	(3)
Mortgage loans, net	4,075	4,817
Below 1.0 | Mortgage loans on real estate
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	15	56
1.0 - 1.25 | Mortgage loans on real estate
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	338	225
1.26 - 1.50 | Mortgage loans on real estate
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	1,089	1,237
Above 1.50 | Mortgage loans on real estate
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	2,700	$ 3,302
2015 and prior | Mortgage loans on real estate
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	1,563
2015 and prior | Below 1.0 | Mortgage loans on real estate
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	15
2015 and prior | 1.0 - 1.25 | Mortgage loans on real estate
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	133
2015 and prior | 1.26 - 1.50 | Mortgage loans on real estate
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	378
2015 and prior | Above 1.50 | Mortgage loans on real estate
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	1,037
2016 | Mortgage loans on real estate
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	464
2016 | Below 1.0 | Mortgage loans on real estate
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	0
2016 | 1.0 - 1.25 | Mortgage loans on real estate
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	27
2016 | 1.26 - 1.50 | Mortgage loans on real estate
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	41
2016 | Above 1.50 | Mortgage loans on real estate
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	396
2017 | Mortgage loans on real estate
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	463
2017 | Below 1.0 | Mortgage loans on real estate
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	0
2017 | 1.0 - 1.25 | Mortgage loans on real estate
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	36
2017 | 1.26 - 1.50 | Mortgage loans on real estate
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	144
2017 | Above 1.50 | Mortgage loans on real estate
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	283
2018 | Mortgage loans on real estate
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	630
2018 | Below 1.0 | Mortgage loans on real estate
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	0
2018 | 1.0 - 1.25 | Mortgage loans on real estate
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	70
2018 | 1.26 - 1.50 | Mortgage loans on real estate
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	187
2018 | Above 1.50 | Mortgage loans on real estate
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	373
2019 | Mortgage loans on real estate
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	880
2019 | Below 1.0 | Mortgage loans on real estate
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	0
2019 | 1.0 - 1.25 | Mortgage loans on real estate
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	48
2019 | 1.26 - 1.50 | Mortgage loans on real estate
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	333
2019 | Above 1.50 | Mortgage loans on real estate
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	499
Current | Mortgage loans on real estate
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	142
Current | Below 1.0 | Mortgage loans on real estate
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	0
Current | 1.0 - 1.25 | Mortgage loans on real estate
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	24
Current | 1.26 - 1.50 | Mortgage loans on real estate
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	6
Current | Above 1.50 | Mortgage loans on real estate
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost before allowance	$ 112