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Post employment benefits - Sensitivity analyses of potential impacts on consolidated income statement and on plan liabilities (Details)
£ in Millions
 12 Months Ended
Jun. 30, 2021
GBP (£)
yr
Jun. 30, 2020
GBP (£)
Jun. 30, 2019
GBP (£)
Disclosure of sensitivity analysis for actuarial assumptions [line items]      
Operating profit £ 3,731 £ 2,137 £ 4,042
Profit for the year £ 2,799 £ 1,454 £ 3,337
Discount rate      
Disclosure of sensitivity analysis for actuarial assumptions [line items]      
Percentage of reasonably possible increase in actuarial assumption 0.50%    
Percentage of reasonably possible decrease in actuarial assumption 0.50%    
Inflation      
Disclosure of sensitivity analysis for actuarial assumptions [line items]      
Percentage of reasonably possible increase in actuarial assumption 0.50%    
Percentage of reasonably possible decrease in actuarial assumption 0.50%    
Life expectancy      
Disclosure of sensitivity analysis for actuarial assumptions [line items]      
Duration of reasonably possible increase in actuarial assumption | yr 1    
United Kingdom | Effect of 0.5% increase in discount rate      
Disclosure of sensitivity analysis for actuarial assumptions [line items]      
Operating profit £ 5    
Profit for the year 18    
Plan liabilities 532    
United Kingdom | Effect of 0.5% decrease in discount rate      
Disclosure of sensitivity analysis for actuarial assumptions [line items]      
Operating profit (5)    
Profit for the year (15)    
Plan liabilities (611)    
United Kingdom | Effect of 0.5% increase in inflation      
Disclosure of sensitivity analysis for actuarial assumptions [line items]      
Operating profit (4)    
Profit for the year (11)    
Plan liabilities (466)    
United Kingdom | Effect of 0.5% decrease in inflation      
Disclosure of sensitivity analysis for actuarial assumptions [line items]      
Operating profit 5    
Profit for the year 10    
Plan liabilities 351    
United Kingdom | Effect of one year increase in life expectancy      
Disclosure of sensitivity analysis for actuarial assumptions [line items]      
Operating profit (1)    
Profit for the year (5)    
Plan liabilities (279)    
Ireland | Effect of 0.5% increase in discount rate      
Disclosure of sensitivity analysis for actuarial assumptions [line items]      
Operating profit 2    
Profit for the year 3    
Plan liabilities 159    
Ireland | Effect of 0.5% decrease in discount rate      
Disclosure of sensitivity analysis for actuarial assumptions [line items]      
Operating profit (2)    
Profit for the year (3)    
Plan liabilities (183)    
Ireland | Effect of 0.5% increase in inflation      
Disclosure of sensitivity analysis for actuarial assumptions [line items]      
Operating profit (1)    
Profit for the year (2)    
Plan liabilities (109)    
Ireland | Effect of 0.5% decrease in inflation      
Disclosure of sensitivity analysis for actuarial assumptions [line items]      
Operating profit 1    
Profit for the year 2    
Plan liabilities 131    
Ireland | Effect of one year increase in life expectancy      
Disclosure of sensitivity analysis for actuarial assumptions [line items]      
Operating profit 0    
Profit for the year (1)    
Plan liabilities (87)    
United States and other | Effect of 0.5% increase in discount rate      
Disclosure of sensitivity analysis for actuarial assumptions [line items]      
Operating profit 1    
Profit for the year 2    
Plan liabilities 26    
United States and other | Effect of 0.5% decrease in discount rate      
Disclosure of sensitivity analysis for actuarial assumptions [line items]      
Operating profit (1)    
Profit for the year (2)    
Plan liabilities (29)    
United States and other | Effect of 0.5% increase in inflation      
Disclosure of sensitivity analysis for actuarial assumptions [line items]      
Operating profit (1)    
Profit for the year (1)    
Plan liabilities (12)    
United States and other | Effect of 0.5% decrease in inflation      
Disclosure of sensitivity analysis for actuarial assumptions [line items]      
Operating profit 1    
Profit for the year 1    
Plan liabilities 12    
United States and other | Effect of one year increase in life expectancy      
Disclosure of sensitivity analysis for actuarial assumptions [line items]      
Operating profit 0    
Profit for the year (1)    
Plan liabilities £ (19)