Investments and Fair Value Measurement - Unrealized Gain (Loss) on Non-Marketable Securities (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Fair Value Disclosures [Abstract]
Upward adjustments	$ 0	$ 0	$ 71	$ 0
Downward adjustments (including impairment)	0	0	0	(1,690)
Total unrealized gain (loss) for non-marketable equity securities	$ 0	$ 0	$ 71	$ (1,690)