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Income Taxes Narrative (Details) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended 12 Months Ended
May 31, 2018
Feb. 28, 2018
May 31, 2017
May 31, 2018
May 31, 2017
Aug. 31, 2019
Aug. 31, 2018
Income Tax Contingency [Line Items]              
Federal statutory rate (35% Prior to Enactment of Tax Act)   35.00%     35.00%    
Provisional benefit from Tax Act   $ (7)          
Benefit from release of valuation allowance   $ (7)          
Effective tax rate 21.70%   0.90% 5.70% 2.50%    
Forecast              
Income Tax Contingency [Line Items]              
Federal statutory rate (35% Prior to Enactment of Tax Act)           21.00% 25.70%