Revision of Previously Issued Financial Statements - Impacts to Consolidated Statements of Income (Loss) and Comprehensive Income (Loss) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended						6 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2025	Jun. 30, 2025	Dec. 31, 2024	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Jun. 30, 2025	Jun. 30, 2024	Sep. 30, 2025	Sep. 30, 2024	Dec. 31, 2024	Dec. 31, 2023
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Impairment of assets to be disposed of	$ 108			$ 32					$ 108	$ 284
Losses (gains) on business disposals	0			(20)					(111)	348
Income before taxes	56			95					(434)	423
Provision (benefit) for income taxes	15			36					(44)	96
Net income (loss)	$ 41			$ 59					$ (390)	$ 327
Net income per share - basic (in dollars per share)	$ 0.16			$ 0.23					$ (1.53)	$ 1.27
Net income per share - diluted (in dollars per share)	$ 0.16			$ 0.23					$ (1.53)	$ 1.27
Comprehensive income (loss)	$ (7)			$ 614					$ 674	$ 463
Comprehensive income (loss) attributable to IFF shareholders	$ (8)			613					$ 672	459
Previously Reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Impairment of assets to be disposed of			$ 33	32	$ 282	$ 0		$ 282		314	$ 347	$ 0
Losses (gains) on business disposals		$ (81)					$ (81)			0
Income before taxes		534	(115)	95	183	115	(460)	298		393	278	(2,518)
Provision (benefit) for income taxes		(78)	(69)	35	11	54	(55)	65		100	31	45
Net income (loss)		612	(46)	60	172	61	(405)	233		293	247	(2,563)
Net income (loss) attributable to IFF shareholders		$ 612	$ (46)	$ 59	$ 170	$ 60	$ (406)	$ 230		$ 289	$ 243	$ (2,567)
Net income per share - basic (in dollars per share)		$ 2.39	$ (0.18)	$ 0.23	$ 0.67	$ 0.23	$ (1.59)	$ 0.90		$ 1.13	$ 0.95	$ (10.05)
Net income per share - diluted (in dollars per share)		$ 2.38	$ (0.18)	$ 0.23	$ 0.66	$ 0.23	$ (1.59)	$ 0.90		$ 1.13	$ 0.95	$ (10.05)
Comprehensive income (loss)		$ 1,320	$ (813)	$ 615	$ 48	$ (234)	$ 707	$ (186)		$ 429	$ (384)	$ (2,261)
Comprehensive income (loss) attributable to IFF shareholders		1,320	(813)	614	46	(235)	706	(189)		425	(388)	(2,265)
Measurement period adjustments
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Impairment of assets to be disposed of			0	0	(30)	0		(30)		(30)	(30)	0
Losses (gains) on business disposals		(30)					(30)			0
Income before taxes		(30)	0	0	30	0	(30)	30		30	30	0
Provision (benefit) for income taxes		(4)	14	1	6	(11)	(4)	(5)		(4)	10	24
Net income (loss)		(26)	(14)	(1)	24	11	(26)	35		34	20	(24)
Net income (loss) attributable to IFF shareholders		$ (26)	$ (14)	$ (1)	$ 24	$ 11	$ (26)	$ 35		$ 34	$ 20	$ (24)
Net income per share - basic (in dollars per share)		$ (0.10)	$ (0.05)	$ 0	$ 0.09	$ 0.05	$ (0.10)	$ 0.14		$ 0.14	$ 0.09	$ (0.09)
Net income per share - diluted (in dollars per share)		$ (0.10)	$ (0.05)	$ 0	$ 0.10	$ 0.05	$ (0.10)	$ 0.14		$ 0.14	$ 0.09	$ (0.09)
Comprehensive income (loss)		$ (26)	$ (14)	$ (1)	$ 24	$ 11	$ (26)	$ 35		$ 34	$ 20	$ (24)
Comprehensive income (loss) attributable to IFF shareholders		(26)	(14)	(1)	24	11	(26)	35		34	20	(24)
Revision Of Prior Period, Revised Amount
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Impairment of assets to be disposed of			33	32	252	0		252		284	317	0
Losses (gains) on business disposals		(111)					(111)			0
Income before taxes		504	(115)	95	213	115	(490)	328		423	308	(2,518)
Provision (benefit) for income taxes		(82)	(55)	36	17	43	(59)	60		96	41	69
Net income (loss)		586	(60)	59	196	72	(431)	268		327	267	(2,587)
Net income (loss) attributable to IFF shareholders		$ 586	$ (60)	$ 58	$ 194	$ 71	$ (432)	$ 265		$ 323	$ 263	$ (2,591)
Net income per share - basic (in dollars per share)		$ 2.29	$ (0.23)	$ 0.23	$ 0.76	$ 0.28	$ (1.69)	$ 1.04		$ 1.27	$ 1.04	$ (10.14)
Net income per share - diluted (in dollars per share)		$ 2.28	$ (0.23)	$ 0.23	$ 0.76	$ 0.28	$ (1.69)	$ 1.04		$ 1.27	$ 1.04	$ (10.14)
Comprehensive income (loss)		$ 1,294	$ (827)	$ 614	$ 72	$ (223)	$ 681	$ (151)		$ 463	$ (364)	$ (2,285)
Comprehensive income (loss) attributable to IFF shareholders		$ 1,294	$ (827)	$ 613	$ 70	$ (224)	$ 680	$ (154)		$ 459	$ (368)	$ (2,289)