Retirement Benefit Obligations - Schedule of Allocation of Plan Assets (Detail) - USD ($) $ in Millions	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2017
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 1,325	$ 1,360	$ 1,389
Investments Net Asset Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,182	1,179
Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	45	64
Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	89	107
Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	9	10	$ 11
Domestic Equity Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	73	73
Domestic Equity Funds [Member] | Investments Net Asset Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	73	73
Domestic Equity Funds [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Domestic Equity Funds [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Domestic Equity Funds [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
International Equity Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	201	206
International Equity Funds [Member] | Investments Net Asset Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	201	206
International Equity Funds [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
International Equity Funds [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
International Equity Funds [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Domestic Fixed Income Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	147	142
Domestic Fixed Income Funds [Member] | Investments Net Asset Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	147	142
Domestic Fixed Income Funds [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Domestic Fixed Income Funds [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Domestic Fixed Income Funds [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
International Fixed Income Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	704	679
International Fixed Income Funds [Member] | Investments Net Asset Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	704	679
International Fixed Income Funds [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
International Fixed Income Funds [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
International Fixed Income Funds [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Balanced Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	146	186
Balanced Funds [Member] | Investments Net Asset Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	57	79
Balanced Funds [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Balanced Funds [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	89	107
Balanced Funds [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	54	74
Other [Member] | Investments Net Asset Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	45	64
Other [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 9	$ 10