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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		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Finite-lived Intangible Assets [Roll Forward]
Finite-lived intangible assets, gross carrying amount	$ 5,626		$ 5,626		$ 5,638
Finite-lived intangible assets, accumulated amortization	(3,728)		(3,728)		(3,622)
Finite-lived intangible assets, net amount	1,898		1,898		2,016
Intangible assets acquired			10
Amortization	(60)	$ (70)	(120)	$ (141)
Foreign exchange			(8)
Client relationships [Member]
Finite-lived Intangible Assets [Roll Forward]
Finite-lived intangible assets, gross carrying amount	3,791		3,791		3,807
Finite-lived intangible assets, accumulated amortization	(2,592)		(2,592)		(2,514)
Finite-lived intangible assets, net amount	1,199		1,199		1,293
Intangible assets acquired			10
Amortization			(96)
Foreign exchange			(8)
Software [Member]
Finite-lived Intangible Assets [Roll Forward]
Finite-lived intangible assets, gross carrying amount	734		734		729
Finite-lived intangible assets, accumulated amortization	(731)		(731)		(726)
Finite-lived intangible assets, net amount	3		3		3
Intangible assets acquired			0
Amortization			0
Foreign exchange			0
Trademark and trade name [Member]
Finite-lived Intangible Assets [Roll Forward]
Finite-lived intangible assets, gross carrying amount	1,038		1,038		1,039
Finite-lived intangible assets, accumulated amortization	(362)		(362)		(342)
Finite-lived intangible assets, net amount	676		676		697
Intangible assets acquired			0
Amortization			(21)
Foreign exchange			0
Other [Member]
Finite-lived Intangible Assets [Roll Forward]
Finite-lived intangible assets, gross carrying amount	63		63		63
Finite-lived intangible assets, accumulated amortization	(43)		(43)		(40)
Finite-lived intangible assets, net amount	$ 20		20		$ 23
Intangible assets acquired			0
Amortization			(3)
Foreign exchange			$ 0