Stockholders' Equity (Share Repurchases) (Details) - USD ($) shares in Millions	12 Months Ended
	Aug. 31, 2018	Jun. 30, 2018	Aug. 31, 2017	Aug. 31, 2016
2016 Share Repurchase Program
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share repurchase program, amount authorized				$ 400,000,000
2017 Share Repurchase Program
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share repurchase program, amount authorized			$ 450,000,000
2018 Share Repurchase Program
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share repurchase program, amount authorized		$ 350,000,000
Shares repurchased (in shares)	0.0
Share repurchase program, remaining authorized repurchase amount	$ 350,000,000