Fair value of financial assets and liabilities - Financial assets subject to offsetting, enforceable master netting arrangements or similar agreements (Detail) - Derivatives [member] - EUR (€) € in Millions	Dec. 31, 2020	Dec. 31, 2019
Fair value of financial assets and liabilities [Line Items]
Gross financial assets subject to offsetting, enforceable master netting arrangements or similar agreements	€ 111	€ 39
Net financial assets subject to offsetting, enforceable master netting arrangements or similar agreements in statement of financial position	111	39
Financial instruments subject to enforceable master netting arrangement or similar agreement not set off against financial assets	55	33
Net financial assets subject to offsetting, enforceable master netting arrangements or similar agreements	€ 57	€ 6