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
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Finite-lived Intangible Assets [Roll Forward]
Finite-lived intangible assets, gross carrying amount	$ 5,632		$ 5,638
Finite-lived intangible assets, accumulated amortization	(3,672)		(3,622)
Finite-lived intangible assets, net amount	1,960		2,016
Intangible assets acquired	10
Amortization	(60)	$ (71)
Foreign exchange	(6)
Client relationships [Member]
Finite-lived Intangible Assets [Roll Forward]
Finite-lived intangible assets, gross carrying amount	3,797		3,807
Finite-lived intangible assets, accumulated amortization	(2,548)		(2,514)
Finite-lived intangible assets, net amount	1,249		1,293
Intangible assets acquired	10
Amortization	(48)
Foreign exchange	(6)
Software [Member]
Finite-lived Intangible Assets [Roll Forward]
Finite-lived intangible assets, gross carrying amount	734		729
Finite-lived intangible assets, accumulated amortization	(731)		(726)
Finite-lived intangible assets, net amount	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		1,039
Finite-lived intangible assets, accumulated amortization	(352)		(342)
Finite-lived intangible assets, net amount	686		697
Intangible assets acquired	0
Amortization	(11)
Foreign exchange	0
Other [Member]
Finite-lived Intangible Assets [Roll Forward]
Finite-lived intangible assets, gross carrying amount	63		63
Finite-lived intangible assets, accumulated amortization	(41)		(40)
Finite-lived intangible assets, net amount	22		$ 23
Intangible assets acquired	0
Amortization	(1)
Foreign exchange	$ 0