Acquisitions and Dispositions of Businesses - Schedule of Consideration Transferred and Preliminary Value of Intangible Assets (Details) - USD ($) $ in Millions		6 Months Ended	12 Months Ended
	Apr. 25, 2024	Jun. 30, 2025	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Assets acquired:
Goodwill			$ 15,797	$ 15,234	$ 8,414
Liabilities assumed:
Payments to acquire businesses, escrow deposits				416
Funds held on behalf of clients			7,378	$ 7,247	$ 6,901
2025 Acquisitions
Consideration transferred:
Cash			915
Deferred and contingent consideration			66
Aggregate consideration transferred			981
Assets acquired:
Goodwill			531
Intangible assets			462
Other assets			228
Total assets acquired			1,221
Liabilities assumed:
Total liabilities assumed			240
Net assets acquired			981
Cash and cash equivalents			43
Funds held on behalf of clients			$ 74
NFP Acquisition
Consideration transferred:
Cash	$ 3,200	$ 3,247
Class A ordinary shares issued		5,882
Aggregate consideration transferred	$ 9,100	9,129
Assets acquired:
Goodwill		6,838
Intangible assets		6,775
Other assets		1,362
Total assets acquired		14,975
Liabilities assumed:
Long-term debt		3,422
Deferred tax liabilities		1,013
Other liabilities		1,218
Total liabilities assumed		5,653
Less: Fair value of redeemable noncontrolling interests		(108)
Less: Fair value of nonredeemable noncontrolling interests		(85)
Net assets acquired		9,129
Cash and cash equivalents		294
Funds held on behalf of clients		277
Accounts payable and accrued liabilities		283
Business combination, recognized liability assumed, lease obligation		$ 125