Other Financial Statement Items - Allowance For Credit Losses (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	$ 94	$ 73	$ 94	$ 73
Current period provision	19	24	60	71
Write-off as uncollectible	(10)	(24)	(35)	(60)
Ending balance	$ 85	$ 73	$ 69	$ 62