Comparative information 2021 - Summary of Reconciliation Between IFRS and IFRS-EU (Detail) - EUR (€) € in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2023	Dec. 31, 2022		Jan. 01, 2022	[1]	Dec. 31, 2020
Disclosure of changes in accounting estimates [line items]
Shareholders' equity	€ 26,372	€ 9,554	€ 10,935	[1],[2]	€ 13,577		€ 24,661
In accordance with IFRS [member]
Disclosure of changes in accounting estimates [line items]
Shareholders' equity		7,475	8,815
In accordance with EU-IFRS [member]
Disclosure of changes in accounting estimates [line items]
Shareholders' equity		€ 7,475	€ 8,815
IFRS4 and IAS39 [member] | Previously Reported [Member]
Disclosure of changes in accounting estimates [line items]
Shareholders' equity, adjustment of EU 'IAS 39' carve-out	632
Shareholders' equity, tax effect of the adjustment	(163)
Shareholders' equity, effect of the adjustment after tax	469
Net income, adjustment of EU 'IAS 39' carve-out	(422)
Net income, tax effect of the adjustment	93
Net income, effect of the adjustment after tax	(328)
IFRS4 and IAS39 [member] | Previously Reported [Member] | In accordance with IFRS [member]
Disclosure of changes in accounting estimates [line items]
Shareholders' equity	23,813
Net income	2,029
IFRS4 and IAS39 [member] | Previously Reported [Member] | In accordance with EU-IFRS [member]
Disclosure of changes in accounting estimates [line items]
Shareholders' equity	24,282
Net income	€ 1,701

[1] Comparatives have been restated due to the initial application of IFRS 9 and IFRS 17. Note 2 includes further details on the changes in accounting policies.

[2] Opening balance as per January 1, 2023 has been restated due to the initial application of IFRS 9 and IFRS 17. Note 2 includes further details on the changes in accounting policies.