Pension and Other Postretirement Benefits - Plan Assets and Grantor Trust Assets By Level (Details) - USD ($) $ in Millions	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2021
Trust for Benefit of Employees
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	$ 276	$ 270
Money market funds | Trust for Benefit of Employees
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	20
Domestic fixed income funds | Trust for Benefit of Employees
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	143
Grantor Trust Balanced Funds | Trust for Benefit of Employees
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	112	234
Grantor Trust Partnership Interest | Trust for Benefit of Employees
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset		16
Other | Trust for Benefit of Employees
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	1	20
Pension benefits
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	853	801	$ 972
Pension benefits | Money market funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	18	20
Pension benefits | Domestic equity funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	189	82
Pension benefits | Domestic fixed income funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	383	381
Pension benefits | International equity funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	136	133
Pension benefits | Balanced funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	78	78
Pension benefits | U.S. Common stocks
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset		43
Pension benefits | Partnership interests
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	49	33
Pension benefits | Exchange traded funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset		32
Pension benefits | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset		(1)
Level 1 | Trust for Benefit of Employees
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	276	254
Level 1 | Money market funds | Trust for Benefit of Employees
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	20
Level 1 | Domestic fixed income funds | Trust for Benefit of Employees
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	143
Level 1 | Grantor Trust Balanced Funds | Trust for Benefit of Employees
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	112	234
Level 1 | Grantor Trust Partnership Interest | Trust for Benefit of Employees
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset		0
Level 1 | Other | Trust for Benefit of Employees
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	1	20
Level 1 | Pension benefits
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	804	768
Level 1 | Pension benefits | Money market funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	18	20
Level 1 | Pension benefits | Domestic equity funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	189	82
Level 1 | Pension benefits | Domestic fixed income funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	383	381
Level 1 | Pension benefits | International equity funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	136	133
Level 1 | Pension benefits | Balanced funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	78	78
Level 1 | Pension benefits | U.S. Common stocks
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset		43
Level 1 | Pension benefits | Partnership interests
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	0	0
Level 1 | Pension benefits | Exchange traded funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset		32
Level 1 | Pension benefits | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset		(1)
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	16
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
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
Fair Value Measured at Net Asset Value Per Share | Grantor Trust 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 | Grantor Trust Partnership Interest | Trust for Benefit of Employees
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset		16
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	49	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 | U.S. Common stocks
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset		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	$ 49	33
Fair Value Measured at Net Asset Value Per Share | Pension benefits | Exchange traded funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset		0
Fair Value Measured at Net Asset Value Per Share | Pension benefits | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset		$ 0