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, 2018	Jun. 30, 2017
Defined Benefit Plan Disclosure [Line Items]
Beginning balance	$ 1,389	$ 1,367
Actual return on plan assets:
Ending balance	1,360	1,389
Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Beginning balance	11	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)	0
Transfers in and out of Level 3	0	0
Ending balance	$ 10	$ 11