Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Allowances for receivables	$ 46	$ 41
Common Class A [Member]
Class of Stock [Line Items]
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	375,000,000	375,000,000
Common stock, shares issued (in shares)	23,000,000	35,000,000
Common Class B [Member]
Class of Stock [Line Items]
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	5,000,000,000	5,000,000,000
Common stock, shares issued (in shares)	852,000,000	838,000,000
Treasury stock, at cost, Class B shares (in shares)	500,000,000	500,000,000