Acquisitions and Dispositions of Businesses - Narrative (Details) shares in Millions, $ in Millions			3 Months Ended		6 Months Ended		98 Months Ended
	Apr. 25, 2024 USD ($) shares	Mar. 01, 2024 USD ($)	Jun. 30, 2025 USD ($) acquisition disposition	Jun. 30, 2024 USD ($) acquisition disposition	Jun. 30, 2025 USD ($) acquisition disposition	Jun. 30, 2024 USD ($) disposition acquisition	Jun. 30, 2025 USD ($)	Jan. 01, 2025	Dec. 31, 2024 USD ($)	May 01, 2017 USD ($)
Business Combination [Line Items]
Number of business acquired under business combination | acquisition			2	8	9	8
Issuance of debt		$ 6,000
Proceeds from long-term lines of credit	$ 2,000
Decrease in goodwill					$ 28
Goodwill			$ 16,024		$ 16,024		$ 16,024		$ 15,234
Number of dispositions | disposition			1		1	3
Gain from sales of businesses			$ 0	$ 257	$ 0	$ 257
Gain on disposition of business				$ 257		257
Deferred consideration on divestiture			$ 88		$ 108	$ 82	192
Disposal Group, Disposed of by Sale, Not Discontinued Operations | May 1, 2017 Divested Business
Business Combination [Line Items]
Purchase price										$ 4,300
Deferred consideration										$ 500
Risk Capital
Business Combination [Line Items]
Number of business acquired under business combination | acquisition			1	5	7	5
Decrease in goodwill					$ 11
Goodwill			$ 9,421		$ 9,421		9,421		8,785
Number of dispositions | disposition				2		2
Human Capital
Business Combination [Line Items]
Number of business acquired under business combination | acquisition			1	3	2	3
Decrease in goodwill					$ 17
Goodwill			$ 6,603		6,603		6,603		$ 6,449
Number of dispositions | disposition						1
Griffiths & Armour
Business Combination [Line Items]
Percentage of capital acquired								100.00%
NFP Acquisition
Business Combination [Line Items]
Percentage of capital acquired	100.00%
Total consideration	$ 9,100				9,129
Cash	$ 3,200				3,247
Number of shares issued for acquisition (up to) | shares	19
Equity interest issued or issuable, value	$ 5,900
Adjustments for cash and certain assumed liabilities	$ 3,900
Increase of intangible assets					125
Decrease of acquired notes receivable					107
Decrease of deferred tax liabilities					110
Decrease in goodwill					115
Goodwill			6,838		$ 6,838		6,838
Weighted average useful life					19 years
NFP Acquisition | Risk Capital
Business Combination [Line Items]
Goodwill			2,600		$ 2,600		2,600
NFP Acquisition | Human Capital
Business Combination [Line Items]
Goodwill			$ 4,200		$ 4,200		$ 4,200