Other Financial Statement Items - Allowance For Credit Losses (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
As of January 1,	$ 73	$ 66
Current period provision	19	21
Write-off as uncollectible	(15)	(17)
As of March 31,	$ 69	$ 62