CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Current assets:
Accounts receivable, allowances for doubtful accounts	$ 204	$ 189
Stockholders' equity:
Common stock, par value (in dollars per share)	$ 0.000006	$ 0.000006
Class A Common Stock
Stockholders' equity:
Common stock, shares authorized (in shares)	5,000,000,000	5,000,000,000
Common stock, shares issued (in shares)	2,404,000,000	2,397,000,000
Common stock, shares outstanding (in shares)	2,404,000,000	2,397,000,000
Class B Common Stock
Stockholders' equity:
Common stock, shares authorized (in shares)	4,141,000,000	4,141,000,000
Common stock, shares issued (in shares)	498,000,000	509,000,000
Common stock, shares outstanding (in shares)	498,000,000	509,000,000