Fair Value Measurements - Debt Securities, Trading, and Equity Securities, FV-NI (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Mar. 31, 2023	Mar. 31, 2022	Mar. 31, 2023	Mar. 31, 2022
Deferred compensation plan assets
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items]
Equity securities, FV-NI, unrealized gain (loss)	$ 2	$ (3)	$ 5	$ 0
Investments in exchange traded funds
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items]
Equity securities, FV-NI, unrealized gain (loss)	$ 12	$ (20)	$ 23	$ (6)

Amount of unrealized gain (loss) on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(3)(d))
-URI https://asc.fasb.org/extlink&oid=120400993&loc=SL114874131-224263

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 321
-SubTopic 10
-Section 50
-Paragraph 4
-URI https://asc.fasb.org/extlink&oid=126980263&loc=SL75117546-209714

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration