Investments - Carrying value for limited partnership interests (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Debt and Equity Securities, FV-NI [Line Items]
Limited partnership interests	$ 7,073	$ 4,563
EMA limited partnerships
Debt and Equity Securities, FV-NI [Line Items]
Limited partnership interests	5,590	3,501
Limited partnership interests
Debt and Equity Securities, FV-NI [Line Items]
Limited partnership interests	1,483	1,062
Private equity
Debt and Equity Securities, FV-NI [Line Items]
Limited partnership interests	5,863	3,655
Private equity | EMA limited partnerships
Debt and Equity Securities, FV-NI [Line Items]
Limited partnership interests	4,439	2,667
Private equity | Limited partnership interests
Debt and Equity Securities, FV-NI [Line Items]
Limited partnership interests	1,424	988
Real estate
Debt and Equity Securities, FV-NI [Line Items]
Limited partnership interests	939	697
Real estate | EMA limited partnerships
Debt and Equity Securities, FV-NI [Line Items]
Limited partnership interests	880	623
Real estate | Limited partnership interests
Debt and Equity Securities, FV-NI [Line Items]
Limited partnership interests	59	74
Other investments
Debt and Equity Securities, FV-NI [Line Items]
Limited partnership interests	271	211
Other investments | EMA limited partnerships
Debt and Equity Securities, FV-NI [Line Items]
Limited partnership interests	271	211
Other investments | Limited partnership interests
Debt and Equity Securities, FV-NI [Line Items]
Limited partnership interests	$ 0	$ 0