Acquisitions and Dispositions of Businesses - Schedule of Consideration Transferred and Preliminary Value of Intangible Assets (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2026	Dec. 31, 2025	Mar. 31, 2025
Assets acquired:
Goodwill	$ 15,925	$ 15,797
Liabilities assumed:
Funds held on behalf of clients	8,286		$ 7,062
ShoreOne Insurance Managers, Inc.
Consideration transferred:
Cash	347
Deferred and contingent consideration	50
Aggregate consideration transferred	397
Assets acquired:
Goodwill	190
Intangible assets	263
Other assets	84
Total assets acquired	537
Liabilities assumed:
Total liabilities assumed	140
Net assets acquired	397
Cash and cash equivalents	29
Funds held on behalf of clients	$ 24