Cash and Cash Equivalents - Additional Information (Detail) - EUR (€) € in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Detailed information about cash and cash equivalents [line items]
Cash received on repurchase agreements	€ 322.0	€ 1,373.0
Cash collateral on securities lended	€ (2,480.0)	€ (3,277.0)
Weighted effective interest rate on short-term deposits	0.39%	0.32%
Short-term deposits maturity days	28 days	31 days
Percentage of deposit with agreed maturity		1.00%
Description of cash flow based on valuation of assets	This deposit is renewed 12 times per year, based on an updated valuation of total assets. The interest received on this deposit is equal to the ECB deposit rate (which was -40bp throughout 2017 and 2018).
Interest received on deposit	0.40%	0.40%
Minimum balance on deposit with Dutch Central Bank		€ 70.0	€ 67.0
Effects of changes in exchange rate	€ 35.0	(196.0)	(23.0)
Increase (decrease) in net cash flows from operating activities	(36.0)	(2,766.0)
Net cash flows from (used in) operating activities	517.0	553.0	3,319.0
Increase (decrease) in net cash flows from investing activities	758.0	(118.0)
Net cash flows from (used in) investing activities	(438.0)	(1,196.0)	(1,078.0)
Business combination consideration transferred	89.0	52.0
Transferred cash and cash equivalents amounted to outflow as result of reinsurance transactions and disposal of entities over which control is lost	8,744.0	10,768.0	11,347.0
Increase (decrease) in net cash flows from financing activities	(2,914.0)	984.0
Net cash flows from (used in) financing activities	(2,395.0)	519.0	(465.0)
Increase (decrease) in net cash flows from operating activities	(36.0)	(2,766.0)
Disposals [member]
Detailed information about cash and cash equivalents [line items]
Consideration received	214.0	299.0
Consideration received in cash and cash equivalents	202.0	306.0
Earn-out	2.0	7.0
Reinsurance transactions and disposal of entities [member]
Detailed information about cash and cash equivalents [line items]
Transferred cash and cash equivalents amounted to outflow as result of reinsurance transactions and disposal of entities over which control is lost	416.0	1,361.0
Securities lending [member]
Detailed information about cash and cash equivalents [line items]
Cash received on repurchase agreements	6,200.0	7,000.0
Cash collateral on securities lended	2.0	7.0
Income from securities lending programs	€ 8.0	€ 11.0	€ 13.0

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Detailed information about cash and cash equivalents.

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Earn- Out paid (received) as part of consideration.

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Income from securities lending programs.

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Increase (decrease) in cash flows from investing activities.

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Increase (decrease) in cash flows from operating activities.

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Interest rate risk on deposits.

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Percentage of deposits with agreed maturity or savings account.

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Short-term deposits maturity.

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Weighted average interest rate on short-term deposits.

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The fair value, at acquisition date, of the consideration transferred in a business combination. [Refer: Business combinations [member]]

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The amount of cash on hand and demand deposits, along with short-term, highly liquid investments that are readily convertible to known amounts of cash and that are subject to an insignificant risk of changes in value. [Refer: Cash; Cash equivalents]

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The cash flows from (used in) financing activities, which are activities that result in changes in the size and composition of the contributed equity and borrowings of the entity.

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The cash flows from (used in) investing activities, which are the acquisition and disposal of long-term assets and other investments not included in cash equivalents.

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The cash flows from (used in) operating activities, which are the principal revenue-producing activities of the entity and other activities that are not investing or financing activities. [Refer: Revenue]

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The amount of consideration paid or received in respect of both obtaining and losing control of subsidiaries or other businesses. [Refer: Subsidiaries [member]]

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The effect of exchange rate changes on cash and cash equivalents held or due in a foreign currency. [Refer: Cash and cash equivalents]

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The amount of reserve that is kept in deposit at a central bank to fulfil regulatory reserve requirements.

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The portion of consideration paid or received, consisting of cash and cash equivalents, in respect of both obtaining and losing control of subsidiaries or other businesses. [Refer: Subsidiaries [member]; Cash and cash equivalents; Consideration paid (received)]

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The amount of instruments sold with the intent to reacquire in repurchase agreements and cash collateral on securities lent.

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The amount of instruments purchased for resale in reverse repurchase agreements and cash collateral on securities borrowed. [Refer: Repurchase agreements and cash collateral on securities lent]

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