v3.26.1
Employee benefit obligations - Schedule of information about maturity profile of defined benefit obligation (Detail)
€ in Millions
 12 Months Ended
Dec. 31, 2025
EUR (€)
Disclosure Of Information About Maturity Profile Of Defined Benefit Obligation [Line Items]  
Estimate of benefit payments expected to be paid from defined benefit plan € 251
Pension Benefits [Member]  
Disclosure Of Information About Maturity Profile Of Defined Benefit Obligation [Line Items]  
Estimate of benefit payments expected to be paid from defined benefit plan 230
Other postretirement benefits [Member]  
Disclosure Of Information About Maturity Profile Of Defined Benefit Obligation [Line Items]  
Estimate of benefit payments expected to be paid from defined benefit plan 15
SES Other post retirement benefits [Member]  
Disclosure Of Information About Maturity Profile Of Defined Benefit Obligation [Line Items]  
Estimate of benefit payments expected to be paid from defined benefit plan 6
Not later than one year [member]  
Disclosure Of Information About Maturity Profile Of Defined Benefit Obligation [Line Items]  
Estimate of benefit payments expected to be paid from defined benefit plan 38
Not later than one year [member] | Pension Benefits [Member]  
Disclosure Of Information About Maturity Profile Of Defined Benefit Obligation [Line Items]  
Estimate of benefit payments expected to be paid from defined benefit plan 35
Not later than one year [member] | Other postretirement benefits [Member]  
Disclosure Of Information About Maturity Profile Of Defined Benefit Obligation [Line Items]  
Estimate of benefit payments expected to be paid from defined benefit plan 2
Not later than one year [member] | SES Other post retirement benefits [Member]  
Disclosure Of Information About Maturity Profile Of Defined Benefit Obligation [Line Items]  
Estimate of benefit payments expected to be paid from defined benefit plan 1
Later than one year and not later than two years [member]  
Disclosure Of Information About Maturity Profile Of Defined Benefit Obligation [Line Items]  
Estimate of benefit payments expected to be paid from defined benefit plan 27
Later than one year and not later than two years [member] | Pension Benefits [Member]  
Disclosure Of Information About Maturity Profile Of Defined Benefit Obligation [Line Items]  
Estimate of benefit payments expected to be paid from defined benefit plan 25
Later than one year and not later than two years [member] | Other postretirement benefits [Member]  
Disclosure Of Information About Maturity Profile Of Defined Benefit Obligation [Line Items]  
Estimate of benefit payments expected to be paid from defined benefit plan 2
Later than one year and not later than two years [member] | SES Other post retirement benefits [Member]  
Disclosure Of Information About Maturity Profile Of Defined Benefit Obligation [Line Items]  
Estimate of benefit payments expected to be paid from defined benefit plan 1
Later than two years and not later than three years [member]  
Disclosure Of Information About Maturity Profile Of Defined Benefit Obligation [Line Items]  
Estimate of benefit payments expected to be paid from defined benefit plan 26
Later than two years and not later than three years [member] | Pension Benefits [Member]  
Disclosure Of Information About Maturity Profile Of Defined Benefit Obligation [Line Items]  
Estimate of benefit payments expected to be paid from defined benefit plan 24
Later than two years and not later than three years [member] | Other postretirement benefits [Member]  
Disclosure Of Information About Maturity Profile Of Defined Benefit Obligation [Line Items]  
Estimate of benefit payments expected to be paid from defined benefit plan 2
Later than two years and not later than three years [member] | SES Other post retirement benefits [Member]  
Disclosure Of Information About Maturity Profile Of Defined Benefit Obligation [Line Items]  
Estimate of benefit payments expected to be paid from defined benefit plan 1
Later than three years and not later than four years [member]  
Disclosure Of Information About Maturity Profile Of Defined Benefit Obligation [Line Items]  
Estimate of benefit payments expected to be paid from defined benefit plan 26
Later than three years and not later than four years [member] | Pension Benefits [Member]  
Disclosure Of Information About Maturity Profile Of Defined Benefit Obligation [Line Items]  
Estimate of benefit payments expected to be paid from defined benefit plan 23
Later than three years and not later than four years [member] | Other postretirement benefits [Member]  
Disclosure Of Information About Maturity Profile Of Defined Benefit Obligation [Line Items]  
Estimate of benefit payments expected to be paid from defined benefit plan 1
Later than three years and not later than four years [member] | SES Other post retirement benefits [Member]  
Disclosure Of Information About Maturity Profile Of Defined Benefit Obligation [Line Items]  
Estimate of benefit payments expected to be paid from defined benefit plan 1
Later than four years and not later than five years [member]  
Disclosure Of Information About Maturity Profile Of Defined Benefit Obligation [Line Items]  
Estimate of benefit payments expected to be paid from defined benefit plan 25
Later than four years and not later than five years [member] | Pension Benefits [Member]  
Disclosure Of Information About Maturity Profile Of Defined Benefit Obligation [Line Items]  
Estimate of benefit payments expected to be paid from defined benefit plan 22
Later than four years and not later than five years [member] | Other postretirement benefits [Member]  
Disclosure Of Information About Maturity Profile Of Defined Benefit Obligation [Line Items]  
Estimate of benefit payments expected to be paid from defined benefit plan 1
Later than four years and not later than five years [member] | SES Other post retirement benefits [Member]  
Disclosure Of Information About Maturity Profile Of Defined Benefit Obligation [Line Items]  
Estimate of benefit payments expected to be paid from defined benefit plan 1
Later than five years [member]  
Disclosure Of Information About Maturity Profile Of Defined Benefit Obligation [Line Items]  
Estimate of benefit payments expected to be paid from defined benefit plan 109
Later than five years [member] | Pension Benefits [Member]  
Disclosure Of Information About Maturity Profile Of Defined Benefit Obligation [Line Items]  
Estimate of benefit payments expected to be paid from defined benefit plan 101
Later than five years [member] | Other postretirement benefits [Member]  
Disclosure Of Information About Maturity Profile Of Defined Benefit Obligation [Line Items]  
Estimate of benefit payments expected to be paid from defined benefit plan 7
Later than five years [member] | SES Other post retirement benefits [Member]  
Disclosure Of Information About Maturity Profile Of Defined Benefit Obligation [Line Items]  
Estimate of benefit payments expected to be paid from defined benefit plan € 1