Retirement Benefit Obligations - Schedule of Allocation of Plan Assets (Detail) - USD ($) $ in Millions	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2018
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 1,319	$ 1,325	$ 1,360
NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,186	1,182
Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	59	45
Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	65	89
Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	9	9	$ 10
Domestic equity funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	60	73
Domestic equity funds | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	60	73
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	186	201
International equity funds | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	186	201
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	145	147
Domestic fixed income funds | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	145	147
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	720	704
International fixed income funds | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	720	704
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	130	146
Balanced funds | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	65	57
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	65	89
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	78	54
Other | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	10	0
Other | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	59	45
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	$ 9	$ 9