Consolidated Balance Sheets - Parenthetical - USD ($) $ in Millions	Jul. 31, 2018	Jul. 31, 2017
Allowance for doubtful accounts	$ 5	$ 46
Preferred stock, $0.01 par value Authorized - 1,345 shares total; 145 shares designated Series A; 250 shares designated Series B Junior Participating Issued and outstanding - None
Preferred Stock, Par Value (in dollars per share)	$ 0.01	$ 0.01
Preferred Stock, Shares Authorized (in shares)	1,345,000	1,345,000
Preferred Stock, Shares Issued (in shares)	0	0
Preferred Stock, Shares Outstanding (in shares)	0	0
Common stock, $0.01 par value Authorized - 750,000 shares Outstanding - 258,616 shares at July 31, 2018 and 255,668 shares at July 31, 2017
Common Stock, Par Value (in dollars per share)	$ 0.01	$ 0.01
Common Stock, Shares Authorized (in shares)	750,000,000	750,000,000
Common Stock, Shares, Outstanding (in shares)	258,616,000	255,668,000
Series A Preferred Stock
Preferred stock, $0.01 par value Authorized - 1,345 shares total; 145 shares designated Series A; 250 shares designated Series B Junior Participating Issued and outstanding - None
Preferred Stock, Shares Authorized (in shares)	145,000	145,000
Series B Preferred Stock
Preferred stock, $0.01 par value Authorized - 1,345 shares total; 145 shares designated Series A; 250 shares designated Series B Junior Participating Issued and outstanding - None
Preferred Stock, Shares Authorized (in shares)	250,000	250,000