Retirement benefit obligations - Fair Value of Plan Assets UK and Canada (Details) - USD ($) $ in Millions	Jul. 31, 2025	Jul. 31, 2024	Jul. 31, 2023
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	$ 1,182	$ 1,308	$ 1,270
Level 1
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	758	510
Level 2
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	46	277
Level 3
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	378	521	$ 510
Equity securities | Canada Plan assets:
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	34	34
Equity securities | Level 1 | Canada Plan assets:
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	34	34
Equity securities | Level 2 | Canada Plan assets:
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0	0
Equity securities | Level 3 | Canada Plan assets:
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0	0
Corporate | U.K. Plan assets:
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		340
Corporate | Canada Plan assets:
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	7	7
Corporate | Level 1 | U.K. Plan assets:
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		1
Corporate | Level 1 | Canada Plan assets:
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0	0
Corporate | Level 2 | U.K. Plan assets:
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		227
Corporate | Level 2 | Canada Plan assets:
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	7	7
Corporate | Level 3 | U.K. Plan assets:
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		112
Corporate | Level 3 | Canada Plan assets:
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0	0
Asset backed | U.K. Plan assets:
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		1
Asset backed | Level 1 | U.K. Plan assets:
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		0
Asset backed | Level 2 | U.K. Plan assets:
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		1
Asset backed | Level 3 | U.K. Plan assets:
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		0
Fixed income security: Government | U.K. Plan assets:
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	705	439
Fixed income security: Government | Canada Plan assets:
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	31	33
Fixed income security: Government | Level 1 | U.K. Plan assets:
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	705	439
Fixed income security: Government | Level 1 | Canada Plan assets:
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0	0
Fixed income security: Government | Level 2 | U.K. Plan assets:
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0	0
Fixed income security: Government | Level 2 | Canada Plan assets:
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	31	33
Fixed income security: Government | Level 3 | U.K. Plan assets:
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0	0
Fixed income security: Government | Level 3 | Canada Plan assets:
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0	0
Cash, cash equivalents and other short-term investments | U.K. Plan assets:
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		23
Cash, cash equivalents and other short-term investments | Level 1 | U.K. Plan assets:
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		22
Cash, cash equivalents and other short-term investments | Level 2 | U.K. Plan assets:
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		1
Cash, cash equivalents and other short-term investments | Level 3 | U.K. Plan assets:
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		0
Cash and cash equivalents | U.K. Plan assets:
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	4
Cash and cash equivalents | Canada Plan assets:
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	2	2
Cash and cash equivalents | Level 1 | U.K. Plan assets:
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	4
Cash and cash equivalents | Level 1 | Canada Plan assets:
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	2	2
Cash and cash equivalents | Level 2 | U.K. Plan assets:
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0
Cash and cash equivalents | Level 2 | Canada Plan assets:
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0	0
Cash and cash equivalents | Level 3 | U.K. Plan assets:
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0
Cash and cash equivalents | Level 3 | Canada Plan assets:
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0	0
Insurance policies | U.K. Plan assets:
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	378	409
Insurance policies | Level 1 | U.K. Plan assets:
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0	0
Insurance policies | Level 2 | U.K. Plan assets:
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0	0
Insurance policies | Level 3 | U.K. Plan assets:
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	378	409
Other | Canada Plan assets:
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	21	20
Other | Level 1 | Canada Plan assets:
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	13	12
Other | Level 2 | Canada Plan assets:
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	8	8
Other | Level 3 | Canada Plan assets:
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	$ 0	$ 0