Retirement Benefit Obligations - Schedule of Allocation of Plan Assets (Detail) - USD ($) $ in Millions	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2016
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 1,360	$ 1,389	$ 1,367
Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	64	55
Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	107	183
Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	10	11	$ 11
Domestic Equity Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	73	78
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	206	196
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	142	151
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	679	642
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	186	255
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	107	182
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	74	67
Other [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	64	55
Other [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	1
Other [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	10	11
Investments Net Asset Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,179	1,140
Investments Net Asset Value [Member] | Domestic Equity Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	73	78
Investments Net Asset Value [Member] | International Equity Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	206	196
Investments Net Asset Value [Member] | Domestic Fixed Income Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	142	151
Investments Net Asset Value [Member] | International Fixed Income Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	679	642
Investments Net Asset Value [Member] | Balanced Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	79	73
Investments Net Asset Value [Member] | Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 0	$ 0