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Goodwill and Other Intangible Assets - Changes in the Net Carrying Amount of the Components of Finite-Lived Intangible Assets (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025	Dec. 31, 2025
Finite-lived Intangible Assets [Roll Forward]
Finite-lived intangible assets, gross carrying amount	$ 5,480		$ 5,480		$ 5,059
Finite-lived intangible assets, accumulated amortization	(4,049)		(4,049)		(3,918)
Finite-lived intangible assets, net amount	1,431		1,431		1,141
Intangible assets acquired			456
Amortization	(59)	$ (47)	(162)	$ (144)
Foreign exchange			(4)
Client relationships [Member]
Finite-lived Intangible Assets [Roll Forward]
Finite-lived intangible assets, gross carrying amount	3,528		3,528		3,239
Finite-lived intangible assets, accumulated amortization	(2,804)		(2,804)		(2,710)
Finite-lived intangible assets, net amount	724		724		529
Intangible assets acquired			318
Amortization			(120)
Foreign exchange			(3)
Software [Member]
Finite-lived Intangible Assets [Roll Forward]
Finite-lived intangible assets, gross carrying amount	849		849		750
Finite-lived intangible assets, accumulated amortization	(755)		(755)		(749)
Finite-lived intangible assets, net amount	94		94		1
Intangible assets acquired			104
Amortization			(10)
Foreign exchange			(1)
Trademark and trade name [Member]
Finite-lived Intangible Assets [Roll Forward]
Finite-lived intangible assets, gross carrying amount	1,044		1,044		1,041
Finite-lived intangible assets, accumulated amortization	(461)		(461)		(430)
Finite-lived intangible assets, net amount	583		583		611
Intangible assets acquired			4
Amortization			(32)
Foreign exchange			0
Other [Member]
Finite-lived Intangible Assets [Roll Forward]
Finite-lived intangible assets, gross carrying amount	59		59		29
Finite-lived intangible assets, accumulated amortization	(29)		(29)		(29)
Finite-lived intangible assets, net amount	$ 30		30		$ 0
Intangible assets acquired			30
Amortization			0
Foreign exchange			$ 0