Stockholders' Equity - Share Repurchases in the Open Market (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended	6 Months Ended
Mar. 31, 2025	Mar. 31, 2024	Mar. 31, 2025	Mar. 31, 2024	Sep. 30, 2024
Equity, Class of Treasury Stock [Line Items]
Total cost	$ 4,473	$ 2,784	$ 8,413	$ 6,393
Unsettled repurchases	$ 4,507		$ 4,507		$ 4,909
Class A common stock
Equity, Class of Treasury Stock [Line Items]
Shares repurchased in the open market (in shares)	13	10	26	25
Average repurchase cost per share (in dollars per share)	$ 340.26	$ 280.41	$ 320.47	$ 255.09
Total cost	$ 4,473	$ 2,784	$ 8,413	$ 6,393
Unsettled repurchases	$ 61		$ 61

Carrying value as of the balance sheet date of obligations incurred and payable, pertaining to costs that are statutory in nature, are incurred on contractual obligations, or accumulate over time and for which invoices have not yet been received or will not be rendered. Examples include taxes, interest, rent and utilities. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

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