Fair Value Measurements - Proceeds from the Sale of Investments (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 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	$ 5	$ 13
Realized gains	0	4
Realized Losses	0	(5)
Interest and dividend income	$ 3	$ 5