Investments - Equity Investments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Increase (Decrease) In Equity Investments [Roll Forward]
Marketable securities, beginning balance	$ 479
Marketable securities, Purchases (Sales), Net	1
Marketable securities, Changes in Fair Value	(5)
Marketable Securities, Other Changes	1
Marketable securities, ending balance	476
Nonmarketable securities, beginning balance	435
Nonmarketable Securities, Purchases (Sales), Net	204
Nonmarketable securities, Changes in Fair Value	35
Non-marketable securities, Other	22
Nonmarketable securities, ending balance	696
Total equity investments, beginning balance	914
Total equity investments, Purchases (Sales), net	205
Total equity investments, Other	23
Total equity investments, Changes in Fair Value	30
Total equity investments, ending balance	1,172
Alternative Investment	157	$ 317
Alternative Investment, Equity Method Investment	539	$ 118
Downwards adjustment on measurement alternative investments	(14)
Upwards adjustment on measurement alternative investments	$ 86