Earnings Per Share (Calculation of Net Earnings Per Common Share (EPS) - Basic and Diluted) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Dec. 31, 2017	Jan. 01, 2017
Earnings Per Share [Abstract]
Net earnings attributable to Starbucks	$ 2,250.2	$ 751.8
Weighted average common shares outstanding (for basic calculation)	1,421.0	1,457.5
Dilutive effect of outstanding common stock options and RSUs	13.6	13.0
Weighted average common and common equivalent shares outstanding (for diluted calculation)	1,434.6	1,470.5
Earnings per share - basic	$ 1.58	$ 0.52
Earnings per share - diluted	$ 1.57	$ 0.51