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Employee Share Ownership Plans - Summary of Description of Plans (Parenthetical) (Detail)
 12 Months Ended
Jun. 30, 2020
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]  
Maximum employee contributions to acquire shares $ 5,000
Share Based Payments Vesting Period 3 years
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
Vesting percentage 100.00%
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%
Long-Term Incentive Plan [member] | Median Total Shareholder Return [member]  
Disclosure of terms and conditions of share-based payment arrangement [line items]  
Vesting percentage 25.00%
Cash and deferred payment plan [member] | First tranche [member]  
Disclosure of terms and conditions of share-based payment arrangement [line items]  
Vesting period 2 years
Cash and deferred payment plan [member] | Second tranche [member]  
Disclosure of terms and conditions of share-based payment arrangement [line items]  
Vesting period 5 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] | MAP awards [member]  
Disclosure of terms and conditions of share-based payment arrangement [line items]  
Vesting period 5 years