Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Receivables, allowance for doubtful accounts	$ 89	$ 118
Preferred stock, par (in dollars per share)	$ 1	$ 1
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Common stock, par (in dollars per share)	$ 0.1667	$ 0.1667
Common stock, shares authorized	300,000,000	300,000,000
Common stock, shares issued	198,572,158	198,495,007
Treasury stock, shares	55,712,062	49,189,811