Summary of accounting policies - Estimated useful lives for significant asset classes (Detail)	Mar. 31, 2026
Minimum [Member] \| Software [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives for significant assets, in years	3 years
Minimum [Member] \| Office buildings [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives for significant assets, in years	3 years
Minimum [Member] \| Equipment and facilities [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives for significant assets, in years	3 years
Maximum [Member] \| Software [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives for significant assets, in years	5 years
Maximum [Member] \| Office buildings [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives for significant assets, in years	50 years
Maximum [Member] \| Equipment and facilities [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives for significant assets, in years	20 years