Accounts Receivable - Activity of Allowance for Doubtful Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	$ 191	$ 106	$ 142
Additions	105	189	145
Deductions	(182)	(104)	(181)
Ending Balance	114	191	106	$ 142
Financing Receivable, Allowance for Credit Loss [Line Items]
Stockholders' equity	11,840	11,162	13,470
Income tax expense	668	450	503
Retained Earnings (Accumulated Deficit)
Financing Receivable, Allowance for Credit Loss [Line Items]
Stockholders' equity	$ (5,998)	$ (8,031)	(6,814)	(1,643)
Income tax expense			2	37
Cumulative Effect, Period of Adoption, Adjustment | Retained Earnings (Accumulated Deficit)
Financing Receivable, Allowance for Credit Loss [Line Items]
Stockholders' equity			9	96
Income tax expense			$ 2	$ (37)