Acquisitions and Dispositions (Allocation of Acquisition Costs) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Dec. 31, 2024	Dec. 31, 2023
Business Acquisition [Line Items]
Cash	$ 37	$ 308
Estimated fair value of deferred/contingent purchase consideration	10	51
Fair value of previously-held equity method investment	15
Total consideration	62	359
Allocation of purchase price:
Goodwill	23,538	$ 17,314	$ 23,306	$ 17,231
Current Fiscal Period Acquisitions
Business Acquisition [Line Items]
Cash	37
Estimated fair value of deferred/contingent purchase consideration	10
Fair value of previously-held equity method investment	15
Total consideration	62
Allocation of purchase price:
Cash and cash equivalents	4
Cash and cash equivalents held in a fiduciary capacity	15
Net receivables	2
Other current assets	1
Goodwill	33
Other intangible assets	24
Right of use assets	1
Other assets	4
Total assets acquired	84
Current liabilities	2
Fiduciary liabilities	15
Other liabilities	5
Total liabilities assumed	22
Net assets acquired	$ 62