Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 33	$ 28
Common stock, par value (in usd per share)	$ 1	$ 1
Common stock, authorized (in shares)	600,000,000	600,000,000
Common stock, issued (in shares)	412,000,000	412,000,000
Common stock, in treasury (in shares)	158,000,000	153,000,000