Investments - Net appreciation (decline) recognized in net income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Debt and Equity Securities, FV-NI [Line Items]
Total	$ 117	$ 178	$ 585	$ 15
Equity securities
Debt and Equity Securities, FV-NI [Line Items]
Total	(20)	105	170	(5)
Limited partnership interests carried at fair value
Debt and Equity Securities, FV-NI [Line Items]
Total	$ 137	$ 73	$ 415	$ 20