Business Combinations - Estimated Fair Values of Aggregate Assets and Liabilities Acquired (Details) - USD ($) $ in Millions			12 Months Ended
	Aug. 01, 2025	Jun. 10, 2025	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Fair Value Of Assets And Liabilities Statement [Line Items]
Cash paid			$ 8,708
Common stock issued			634	$ 0	$ 18
Common stock issued			634
Other payable			712
Recorded earn-out payable			58	$ 73	$ 67
Total consideration			10,112
Maximum potential earn-out payable			186
Allocation of purchase price:
Cash and cash equivalents			316
Fiduciary cash			538
Commission, fees, and other receivables			435
Fiduciary receivables			460
Other current assets			851
Goodwill			6,885
Other assets			127
Total assets acquired			12,983
Fiduciary liabilities			(992)
Accounts payable and accrued expenses			(735)
Other current liabilities			(776)
Deferred income tax, net			(80)
Other long-term liabilities			(288)
Total liabilities assumed			(2,871)
Net assets acquired			10,112
NBS Insurance Agency | Specialty Distribution
Fair Value Of Assets And Liabilities Statement [Line Items]
Cash paid			54
Common stock issued			0
Other payable			0
Recorded earn-out payable			0
Total consideration			54
Maximum potential earn-out payable			0
Allocation of purchase price:
Cash and cash equivalents			(0)
Fiduciary cash			14
Commission, fees, and other receivables			4
Fiduciary receivables			(0)
Other current assets			0
Goodwill			34
Other assets			0
Total assets acquired			68
Fiduciary liabilities			(13)
Accounts payable and accrued expenses			0
Other current liabilities			(1)
Deferred income tax, net			0
Other long-term liabilities			0
Total liabilities assumed			(14)
Net assets acquired			54
Tim Parkman, Inc. | Specialty Distribution
Fair Value Of Assets And Liabilities Statement [Line Items]
Cash paid			69
Common stock issued			0
Other payable			6
Recorded earn-out payable			7
Total consideration			82
Maximum potential earn-out payable			23
Allocation of purchase price:
Cash and cash equivalents			0
Fiduciary cash			0
Commission, fees, and other receivables			0
Fiduciary receivables			0
Other current assets			0
Goodwill			62
Other assets			1
Total assets acquired			82
Fiduciary liabilities			0
Accounts payable and accrued expenses			0
Other current liabilities			0
Deferred income tax, net			0
Other long-term liabilities			0
Total liabilities assumed			0
Net assets acquired			82
Poulton Associates, LLC | Specialty Distribution
Fair Value Of Assets And Liabilities Statement [Line Items]
Cash paid			168
Common stock issued			21
Other payable			1
Recorded earn-out payable			20
Total consideration			210
Maximum potential earn-out payable			104
Allocation of purchase price:
Cash and cash equivalents			0
Fiduciary cash			0
Commission, fees, and other receivables			0
Fiduciary receivables			0
Other current assets			0
Goodwill			141
Other assets			0
Total assets acquired			210
Fiduciary liabilities			0
Accounts payable and accrued expenses			0
Other current liabilities			0
Deferred income tax, net			0
Other long-term liabilities			0
Total liabilities assumed			0
Net assets acquired			210
RSC Topco, Inc.
Fair Value Of Assets And Liabilities Statement [Line Items]
Common stock issued	$ 613	$ 1,045
RSC Topco, Inc. | Retail and Specialty Distribution
Fair Value Of Assets And Liabilities Statement [Line Items]
Cash paid			8,293
Common stock issued			613
Other payable			702
Recorded earn-out payable			0
Total consideration			9,608
Maximum potential earn-out payable			0
Allocation of purchase price:
Cash and cash equivalents			314
Fiduciary cash			516
Commission, fees, and other receivables			430
Fiduciary receivables			437
Other current assets			851
Goodwill			6,547
Other assets			111
Total assets acquired			12,427
Fiduciary liabilities			(957)
Accounts payable and accrued expenses			(722)
Other current liabilities			(775)
Deferred income tax, net			(80)
Other long-term liabilities			(285)
Total liabilities assumed			(2,819)
Net assets acquired			9,608
Other Acquisitions | Retail and Specialty Distribution
Fair Value Of Assets And Liabilities Statement [Line Items]
Cash paid			124
Common stock issued			0
Other payable			3
Recorded earn-out payable			31
Total consideration			158
Maximum potential earn-out payable			59
Allocation of purchase price:
Cash and cash equivalents			2
Fiduciary cash			8
Commission, fees, and other receivables			1
Fiduciary receivables			23
Other current assets			0
Goodwill			101
Other assets			15
Total assets acquired			196
Fiduciary liabilities			(22)
Accounts payable and accrued expenses			(13)
Other current liabilities			0
Deferred income tax, net			0
Other long-term liabilities			(3)
Total liabilities assumed			(38)
Net assets acquired			158
Purchased Customer Accounts and Other
Allocation of purchase price:
Purchased customer accounts and other intangibles			3,371
Purchased Customer Accounts and Other | NBS Insurance Agency | Specialty Distribution
Allocation of purchase price:
Purchased customer accounts and other intangibles			16
Purchased Customer Accounts and Other | Tim Parkman, Inc. | Specialty Distribution
Allocation of purchase price:
Purchased customer accounts and other intangibles			19
Purchased Customer Accounts and Other | Poulton Associates, LLC | Specialty Distribution
Allocation of purchase price:
Purchased customer accounts and other intangibles			69
Purchased Customer Accounts and Other | RSC Topco, Inc. | Retail and Specialty Distribution
Allocation of purchase price:
Purchased customer accounts and other intangibles			3,221
Purchased Customer Accounts and Other | Other Acquisitions | Retail and Specialty Distribution
Allocation of purchase price:
Purchased customer accounts and other intangibles			$ 46