Immediate recognition actuarial gains (losses) arising from change in assumption recognized in profit (loss).

No definition available.

Name:	cstm_ImmediateRecognitionActuarialGainsLossesArisingFromChangeInAssumptionRecognizedInProfitLoss
Namespace Prefix:	cstm_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The decrease (increase) in a net defined benefit liability (asset) resulting from actuarial gains (losses) arising from changes in demographic assumptions that result in remeasurements of the net defined benefit liability (asset). Demographic assumptions deal with matters such as: (a) mortality; (b) rates of employee turnover, disability and early retirement; (c) the proportion of plan members with dependants who will be eligible for benefits; (d) the proportion of plan members who will select each form of payment option available under the plan terms; and (e) claim rates under medical plans. [Refer: Net defined benefit liability (asset)]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 19
-IssueDate 2019-01-01
-Paragraph 141
-Subparagraph c
-Clause ii
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=19&code=ifrs-tx-2019-en-r&anchor=para_141_c_ii&doctype=Standard
-URIDate 2019-03-27

PENSIONS AND OTHER POST-EMPLOYMENT BENEFIT OBLIGATIONS - Movement in Net Defined Benefit Obligations (Details) € in Millions, $ in Millions	3 Months Ended		6 Months Ended			12 Months Ended
	Jun. 30, 2020 EUR (€)	Jun. 30, 2019 EUR (€)	Jun. 30, 2020 EUR (€)	Jun. 30, 2020 USD ($)	Jun. 30, 2019 EUR (€)	Dec. 31, 2019 EUR (€)	Dec. 31, 2018 EUR (€)
Disclosure of net defined benefit liability (asset) [line items]
Beginning balance			€ 670	$ 670
Remeasurements due to:
Closing balance	€ 715		715			€ 670
Included in the Unaudited Interim Consolidated Income Statement
Disclosure of net defined benefit liability (asset) [line items]
Current service cost	6	€ 6	14		€ 12
Interest cost / (income)	3	4	6		8
Past service cost	2	0	2		0
Immediate recognition of gains / (losses) arising over the year	1	2	0		2
Administration expenses	1	0	1		1
Included in the Unaudited Interim Consolidated Statement of Comprehensive Income / (Loss)
Remeasurements due to:
—actual return less interest on plan assets			13
—changes in financial assumptions			27
—changes in demographic assumptions			0
—experience losses			0
Effects of changes in foreign exchange rates			2
Included in the Unaudited Interim Consolidated Statement of Cash Flows
Remeasurements due to:
Benefits paid			(10)
Contributions by the Group			(10)
Contributions by the plan participants			0
Pension Benefits \| Included in the Unaudited Interim Consolidated Income Statement
Disclosure of net defined benefit liability (asset) [line items]
Current service cost	5	5	11		9
Interest cost / (income)	2	2	3		4
Past service cost	0	0	0		0
Immediate recognition of gains / (losses) arising over the year	0	0	0		0
Administration expenses	1	0	1		1
Other Benefits
Disclosure of net defined benefit liability (asset) [line items]
Past service cost			2			3	€ 36
Other Benefits \| Included in the Unaudited Interim Consolidated Income Statement
Disclosure of net defined benefit liability (asset) [line items]
Current service cost	1	1	3		3
Interest cost / (income)	1	2	3		4
Past service cost	2	0	2		0
Immediate recognition of gains / (losses) arising over the year	1	2	0		2
Administration expenses	0	€ 0	0		€ 0
Defined benefit obligations
Disclosure of net defined benefit liability (asset) [line items]
Beginning balance			1,115
Remeasurements due to:
Closing balance	1,150		1,150			1,115
Defined benefit obligations \| Included in the Unaudited Interim Consolidated Income Statement
Disclosure of net defined benefit liability (asset) [line items]
Current service cost			14
Interest cost / (income)			10
Past service cost			2
Immediate recognition of gains / (losses) arising over the year			0
Administration expenses			0
Defined benefit obligations \| Included in the Unaudited Interim Consolidated Statement of Comprehensive Income / (Loss)
Remeasurements due to:
—actual return less interest on plan assets			0
—changes in financial assumptions			27
—changes in demographic assumptions			0
—experience losses			0
Effects of changes in foreign exchange rates			7
Defined benefit obligations \| Included in the Unaudited Interim Consolidated Statement of Cash Flows
Remeasurements due to:
Benefits paid			(27)
Contributions by the Group			0
Contributions by the plan participants			2
Defined benefit obligations \| Pension Benefits
Disclosure of net defined benefit liability (asset) [line items]
Beginning balance			895
Remeasurements due to:
Closing balance	920		920			895
Defined benefit obligations \| Pension Benefits \| Included in the Unaudited Interim Consolidated Income Statement
Disclosure of net defined benefit liability (asset) [line items]
Current service cost			11
Interest cost / (income)			7
Past service cost			0
Immediate recognition of gains / (losses) arising over the year			0
Administration expenses			0
Defined benefit obligations \| Pension Benefits \| Included in the Unaudited Interim Consolidated Statement of Comprehensive Income / (Loss)
Remeasurements due to:
—actual return less interest on plan assets			0
—changes in financial assumptions			16
—changes in demographic assumptions			0
—experience losses			1
Effects of changes in foreign exchange rates			6
Defined benefit obligations \| Pension Benefits \| Included in the Unaudited Interim Consolidated Statement of Cash Flows
Remeasurements due to:
Benefits paid			(18)
Contributions by the Group			0
Contributions by the plan participants			2
Defined benefit obligations \| Other Benefits
Disclosure of net defined benefit liability (asset) [line items]
Beginning balance			220
Remeasurements due to:
Closing balance	230		230			220
Defined benefit obligations \| Other Benefits \| Included in the Unaudited Interim Consolidated Income Statement
Disclosure of net defined benefit liability (asset) [line items]
Current service cost			3
Interest cost / (income)			3
Past service cost			2
Immediate recognition of gains / (losses) arising over the year			0
Administration expenses			0
Defined benefit obligations \| Other Benefits \| Included in the Unaudited Interim Consolidated Statement of Comprehensive Income / (Loss)
Remeasurements due to:
—actual return less interest on plan assets			0
—changes in financial assumptions			11
—changes in demographic assumptions			0
—experience losses			(1)
Effects of changes in foreign exchange rates			1
Defined benefit obligations \| Other Benefits \| Included in the Unaudited Interim Consolidated Statement of Cash Flows
Remeasurements due to:
Benefits paid			(9)
Contributions by the Group			0
Contributions by the plan participants			0
Plan Assets
Disclosure of net defined benefit liability (asset) [line items]
Beginning balance			(445)
Remeasurements due to:
Closing balance	€ (435)		(435)			€ (445)
Plan Assets \| Included in the Unaudited Interim Consolidated Income Statement
Disclosure of net defined benefit liability (asset) [line items]
Current service cost			0
Interest cost / (income)			(4)
Past service cost			0
Immediate recognition of gains / (losses) arising over the year			0
Administration expenses			1
Plan Assets \| Included in the Unaudited Interim Consolidated Statement of Comprehensive Income / (Loss)
Remeasurements due to:
—actual return less interest on plan assets			13
—changes in financial assumptions			0
—changes in demographic assumptions			0
—experience losses			0
Effects of changes in foreign exchange rates			(5)
Plan Assets \| Included in the Unaudited Interim Consolidated Statement of Cash Flows
Remeasurements due to:
Benefits paid			17
Contributions by the Group			(10)
Contributions by the plan participants			€ (2)