Pension and Other Postretirement Benefits - Schedule of Plan Assets and Grantor Trust Assets By Level (Details) - USD ($) $ in Millions	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2024
Trust for Benefit of Employees
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	$ 262	$ 265
Money market funds | Trust for Benefit of Employees
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	1	8
Domestic fixed income funds | Trust for Benefit of Employees
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	132	68
Balanced funds | Trust for Benefit of Employees
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	15	60
Domestic government obligations | Trust for Benefit of Employees
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	113	128
Other | Trust for Benefit of Employees
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	1	1
Pension benefits
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	921	904	$ 891
Pension benefits | Money market funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	43	35
Pension benefits | Domestic equity funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	105	116
Pension benefits | Domestic fixed income funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	588	582
Pension benefits | International equity funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	87	83
Pension benefits | Balanced funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	63	55
Pension benefits | Partnership interests
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	35	33
Level 1 | Trust for Benefit of Employees
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	262	265
Level 1 | Money market funds | Trust for Benefit of Employees
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	1	8
Level 1 | Domestic fixed income funds | Trust for Benefit of Employees
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	132	68
Level 1 | Balanced funds | Trust for Benefit of Employees
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	15	60
Level 1 | Domestic government obligations | Trust for Benefit of Employees
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	113	128
Level 1 | Other | Trust for Benefit of Employees
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	1	1
Level 1 | Pension benefits
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	886	871
Level 1 | Pension benefits | Money market funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	43	35
Level 1 | Pension benefits | Domestic equity funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	105	116
Level 1 | Pension benefits | Domestic fixed income funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	588	582
Level 1 | Pension benefits | International equity funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	87	83
Level 1 | Pension benefits | Balanced funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	63	55
Level 1 | Pension benefits | Partnership interests
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	0	0
Fair Value Measured at Net Asset Value Per Share | Trust for Benefit of Employees
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	0	0
Fair Value Measured at Net Asset Value Per Share | Money market funds | Trust for Benefit of Employees
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	0	0
Fair Value Measured at Net Asset Value Per Share | Domestic fixed income funds | Trust for Benefit of Employees
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	0	0
Fair Value Measured at Net Asset Value Per Share | Balanced funds | Trust for Benefit of Employees
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	0	0
Fair Value Measured at Net Asset Value Per Share | Domestic government obligations | Trust for Benefit of Employees
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	0	0
Fair Value Measured at Net Asset Value Per Share | Other | Trust for Benefit of Employees
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	0	0
Fair Value Measured at Net Asset Value Per Share | Pension benefits
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	35	33
Fair Value Measured at Net Asset Value Per Share | Pension benefits | Money market funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	0	0
Fair Value Measured at Net Asset Value Per Share | Pension benefits | Domestic equity funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	0	0
Fair Value Measured at Net Asset Value Per Share | Pension benefits | Domestic fixed income funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	0	0
Fair Value Measured at Net Asset Value Per Share | Pension benefits | International equity funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	0	0
Fair Value Measured at Net Asset Value Per Share | Pension benefits | Balanced funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	0	0
Fair Value Measured at Net Asset Value Per Share | Pension benefits | Partnership interests
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	$ 35	$ 33