Fair Value - Schedule of Transfers between Level 1 and Level II for Financial Assets and Liabilities Recorded at Fair Value on Recurring Basis (Detail) - Recurring fair value measurement [member] - EUR (€) € in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Disclosure of transfers between level 1 and level 2 for financial assets and liabilities recorded at fair value [line items]
Transfers Level I to Level II	€ 44
Transfers Level II to Level I	32	€ 46
Available-for-sale financial assets [member]
Disclosure of transfers between level 1 and level 2 for financial assets and liabilities recorded at fair value [line items]
Transfers Level I to Level II	44
Transfers Level II to Level I	32	46
Available-for-sale financial assets [member] | Debt securities [member]
Disclosure of transfers between level 1 and level 2 for financial assets and liabilities recorded at fair value [line items]
Transfers Level I to Level II	44
Transfers Level II to Level I	€ 32	€ 46