Acquisitions and Dispositions (Allocation of Acquisition Costs) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Dec. 31, 2024	Dec. 31, 2023
Business Combination [Line Items]
Cash	$ 254	$ 1,100
Estimated fair value of deferred/contingent purchase consideration	68	176
Fair value of previously-held equity method investment	15
Total consideration	337	1,300
Allocation of purchase price:
Goodwill	23,949	$ 18,235	$ 23,306	$ 17,231
Current Fiscal Period Acquisitions
Business Combination [Line Items]
Cash	254
Estimated fair value of deferred/contingent purchase consideration	68
Fair value of previously-held equity method investment	15
Total consideration	337
Allocation of purchase price:
Cash and cash equivalents	13
Cash and cash equivalents held in a fiduciary capacity	17
Net receivables	22
Other current assets	2
Goodwill	234
Other intangible assets	100
Fixed assets, net	1
Right of use assets	4
Other assets	4
Total assets acquired	397
Current liabilities	17
Fiduciary liabilities	17
Other liabilities	26
Total liabilities assumed	60
Net assets acquired	$ 337