Investments - Net appreciation (decline) recognized in net income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Debt and Equity Securities, FV-NI [Line Items]
Total	$ 269	$ 170	$ 504	$ (168)
Equity securities
Debt and Equity Securities, FV-NI [Line Items]
Total	132	196	226	(114)
Limited partnership interests carried at fair value
Debt and Equity Securities, FV-NI [Line Items]
Total	$ 137	$ (26)	$ 278	$ (54)