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Employee Share Ownership Plans - Summary of Description of Plans (Parenthetical) (Detail) | 12 Months Ended
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Jun. 30, 2018 USD ($)
STIP and GSTIP [member] |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |
Vesting period | 2 years
Shareplus [member] |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |
Vesting period | 3 years
Maximum employee contributions to acquire shares | $ 5,000
Long-Term Incentive Plan [member] |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |
Vesting percentage per year | 5.50%
Vesting period | 5 years
Long-Term Incentive Plan [member] | Peer Group Total Shareholder Return [Member] |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |
Vesting percentage | 67.00%
Long-Term Incentive Plan [member] | Index Total Shareholder Return [Member] |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |
Vesting percentage | 33.00%
Bottom of range [Member] | Transitional OMC awards [member] |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |
Vesting period | 3 years
Bottom of range [Member] | MAP awards [member] |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |
Vesting period | 1 year
Top of range [Member] | Transitional OMC awards [member] |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |
Vesting period | 4 years
Top of range [Member] | MAP awards [member] |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |
Vesting period | 5 years

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- Definition Maximum contributions of employee to acquire shares in share based arrangement plans. + References No definition available. + Details
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- Definition Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes of the table. + References No definition available. + Details
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- Details
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- Details
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