Business Combinations - Additional Information (Details) $ in Millions		6 Months Ended
	Jun. 30, 2024 USD ($)	Jun. 30, 2024 USD ($) Acquisition	Mar. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)	Jun. 30, 2023 USD ($)	Mar. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Business Acquisition [Line Items]
Number of acquisitions | Acquisition		18
Measurement period adjustment, fiduciary assets		$ 20
Measurement period adjustment, fiduciary liabilities		20
Measurement period adjustment, goodwill		13
Cash paid	$ 4
Measurement period adjustment, deferred consideration		5
Measurement period adjustment, non-controlling interest		6
Net assets acquired	147	147
Aggregate purchase price of acquisitions		(2)
Total consideration	147	147
Goodwill	108	108
Estimated acquisition earn-out payables	169	169	$ 203	$ 249	$ 232	$ 254	$ 252
Maximum future contingency payments acquisitions	485	485
Other Noncurrent Liabilities
Business Acquisition [Line Items]
Estimated acquisition earn-out payables	76	76
Accounts payable
Business Acquisition [Line Items]
Estimated acquisition earn-out payables	93	93
Retail
Business Acquisition [Line Items]
Measurement period adjustment, goodwill		6
Wholesale Brokerage
Business Acquisition [Line Items]
Measurement period adjustment, goodwill		$ 6
Purchased Customer Accounts
Business Acquisition [Line Items]
Weighted average life (years)		15 years
Business Combinations - Stock Deals
Business Acquisition [Line Items]
Number of acquisitions | Acquisition		5
Assets and Assumed Certain Liabilities
Business Acquisition [Line Items]
Number of acquisitions | Acquisition		8
Book of Business Purchases
Business Acquisition [Line Items]
Number of acquisitions | Acquisition		5
Other Acquisitions | Maximum
Business Acquisition [Line Items]
Total consideration	$ 50	$ 50