Fair Value Measurements - Proceeds from the Sale of Investments (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Proceeds from the sale of investments in available-for-sale securities, realized gains and losses on those sales, and interest and dividend income
Sale proceeds	$ 16	$ 6	$ 29	$ 45
Realized gains	0	0	0	4
Realized Losses	(1)	0	(2)	(7)
Interest and dividend income	$ 3	$ 4	$ 8	$ 18