Retirement Benefit Obligations - Summary of Changes in Fair Value of Investments Reflected as Level 3 Assets (Detail) - USD ($) $ in Millions	12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Defined Benefit Plan Disclosure [Line Items]
Beginning balance	$ 1,360	$ 1,389
Actual return on plan assets:
Ending balance	1,325	1,360
Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Beginning balance	10	11
Actual return on plan assets:
Actual return on plan assets, Relating to assets still held at end of period	0	0
Actual return on plan assets, Relating to assets sold during the period	0	0
Purchases, sales, settlements and issuances	(1)	(1)
Transfers in and out of Level 3	0	0
Ending balance	$ 9	$ 10