Risk Management Activities and Fair Value Measurements - Notional Amounts And Fair Values Of Qualifying And Non-Qualifying Financial Instruments Used In Hedging Transactions (Details) - USD ($) $ in Millions	Sep. 30, 2025	Jun. 30, 2025
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amount	$ 22,202	$ 18,730
Fair Value Asset	11	19
Fair Value (Liability)	(786)	(1,062)
Designated as Hedging Instrument
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amount	17,863	15,154
Fair Value Asset	7	0
Fair Value (Liability)	(777)	(1,061)
Interest rate contracts | Fair Value Hedging
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amount	3,283	3,280
Fair Value Asset	0	0
Fair Value (Liability)	(195)	(201)
Foreign currency interest rate contracts | Not Designated as Hedging Instrument
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amount	4,339	3,576
Fair Value Asset	3	19
Fair Value (Liability)	(9)	0
Foreign currency interest rate contracts | Net Investment Hedging
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amount	14,581	11,874
Fair Value Asset	7	0
Fair Value (Liability)	$ (582)	$ (860)