Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 10	$ 9
Preferred stock:
Shares issued	0	0
Shares outstanding	0	0
Par value	$ 0.01
Shares authorized	30,000,000
Common stock:
Shares issued	978,000,000	975,000,000
Par value	$ 0.01
Shares authorized	2,000,000,000
Treasury stock	(318,000,000)	(295,000,000)

Amount of allowance for credit loss on accounts receivable, classified as current.

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