Summary of Significant Accounting Policies - Shares Used in Computing Basic and Diluted Earnings Per Share (Details) - shares shares in Thousands	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Denominator:
Weighted-average common shares outstanding - basic (in shares)	208,774	209,439
Incremental shares issuable for stock options and awards (in shares)	866	1,819
Weighted-average common shares outstanding - diluted (in shares)	209,640	211,258
Antidilutive securities excluded from computation of earnings per share (in shares)	6,000	3,499