Restructuring Costs (Restructuring Activity) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Restructuring Reserve [Roll Forward]
Restructuring charges	$ 276	$ 301
Restructuring charges, statement of income or comprehensive income [Extensible Enumeration]		Operating Expenses
JLT Transaction
Restructuring Reserve [Roll Forward]
Beginning of period	130	$ 146
Restructuring charges	276	301
Cash payments	(270)	(271)
Non-cash charges	(19)	(46)
End of period	117	130
JLT Transaction | Severance
Restructuring Reserve [Roll Forward]
Beginning of period	89	88
Restructuring charges	163	148
Cash payments	(177)	(147)
Non-cash charges	0	0
End of period	75	89
JLT Transaction | Real Estate Related Costs
Restructuring Reserve [Roll Forward]
Beginning of period	39	56
Restructuring charges	66	96
Cash payments	(45)	(69)
Non-cash charges	(18)	(44)
End of period	42	39
JLT Transaction | Information Technology
Restructuring Reserve [Roll Forward]
Beginning of period	0	0
Restructuring charges	25	15
Cash payments	(24)	(13)
Non-cash charges	(1)	(2)
End of period	0	0
JLT Transaction | Consulting and Other Outside Services
Restructuring Reserve [Roll Forward]
Beginning of period	2	2
Restructuring charges	22	42
Cash payments	(24)	(42)
Non-cash charges	0	0
End of period	$ 0	$ 2