UNAUDITED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Amortized cost of available-for-sale debt securities, current	$ 0	$ 998
Accounts receivable, allowance for credit loss	208	49
Prepaid expenses, allowance for credit loss, current	16	6
Amortized cost of available-for-sale debt securities, noncurrent	775	2,192
Prepaid expenses, allowance for credit loss, noncurrent	$ 38	$ 0
Common stock, par value (in dollars per share)	$ 0.008	$ 0.008
Common stock, shares authorized (in shares)	1,000,000,000	1,000,000,000
Common stock, shares issued (in shares)	63,398,711	63,179,471
Treasury stock, shares (in shares)	22,444,443	21,762,070