Investments (Details) - Equity Securities - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Investment disclosure details
Equity securities, cost	$ 387	$ 376
Gross gains	78	52
Gross losses	12	3
Equity securities, at fair value	453	425
Net recognized gains (losses) on equity securities still held	25	61
Public common stock [Member]
Investment disclosure details
Equity securities, cost	352	341
Gross gains	70	45
Gross losses	12	3
Equity securities, at fair value	410	383
Non-redeemable preferred stock [Member]
Investment disclosure details
Equity securities, cost	35	35
Gross gains	8	7
Gross losses	0	0
Equity securities, at fair value	$ 43	$ 42