Retirement Benefit Obligations - Schedule of Allocation of Plan Assets (Detail) - USD ($) $ in Millions	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 1,447	$ 1,319	$ 1,325
NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,317	1,186
Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	53	59
Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	67	65
Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	10	9	$ 9
Domestic equity funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	61	60
Domestic equity funds | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	61	60
Domestic equity funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Domestic equity funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Domestic equity funds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
International equity funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	199	186
International equity funds | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	199	186
International equity funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
International equity funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
International equity funds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Domestic fixed income funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	144	145
Domestic fixed income funds | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	144	145
Domestic fixed income funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Domestic fixed income funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Domestic fixed income funds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
International fixed income funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	882	720
International fixed income funds | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	882	720
International fixed income funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
International fixed income funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
International fixed income funds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Balanced funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	67	130
Balanced funds | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	65
Balanced funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Balanced funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	67	65
Balanced funds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	94	78
Other | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	31	10
Other | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	53	59
Other | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 10	$ 9