Acquisitions and Dispositions of Businesses - Narrative (Details) shares in Millions			3 Months Ended			9 Months Ended
	Apr. 25, 2024 USD ($) employee shares	Mar. 01, 2024 USD ($)	Sep. 30, 2024 USD ($) acquisition	Jun. 30, 2024 USD ($)	Sep. 30, 2023 USD ($) acquisition	Sep. 30, 2024 USD ($) acquisition	Sep. 30, 2023 USD ($) acquisition	Dec. 31, 2023 USD ($)
Business Acquisition [Line Items]
Number of business acquired under business combination | acquisition			8		1	15	2
Issuance of debt		$ 6,000,000,000
Proceeds from long-term lines of credit	$ 2,000,000,000
Goodwill			$ 15,612,000,000			$ 15,612,000,000		$ 8,414,000,000
Intangible assets, net			6,789,000,000			6,789,000,000		234,000,000
Extinguishment of debt				$ 6,000,000
Tradenames
Business Acquisition [Line Items]
Intangible assets, net			767,000,000			767,000,000		$ 0
NFP Acquisition
Business Acquisition [Line Items]
Number of colleagues (more than) | employee	7,700
NFP Acquisition
Business Acquisition [Line Items]
Total consideration	$ 9,100,000,000					9,129,000,000
Percentage of capital acquired	100.00%
Cash	$ 3,200,000,000					3,247,000,000
Number of shares issued for acquisition (in shares) | shares	19
Equity interest issued or issuable, value	$ 5,900,000,000
Adjustments for cash and certain assumed liabilities	$ 3,900,000,000
Decrease of acquired assets			106,000,000
Decrease of assumed liabilities			77,000,000
Increase in fair value of redeemable noncontrolling interests			5,000,000
Increase in goodwill			34,000,000
Goodwill			6,987,000,000			$ 6,987,000,000
Weighted average useful life						19 years
Intangible assets, net			6,700,000,000			$ 6,700,000,000
Acquisition related costs			1,000,000			$ 90,000,000
NFP Acquisition | Customer Relationships
Business Acquisition [Line Items]
Weighted average useful life						20 years
NFP Acquisition | Tradenames
Business Acquisition [Line Items]
Weighted average useful life						10 years
NFP Acquisition | Technology and other
Business Acquisition [Line Items]
Weighted average useful life						7 years
Other Acquisitions
Business Acquisition [Line Items]
Total consideration			280,000,000		$ 14,000,000	$ 396,000,000	$ 23,000,000
Cash						377,000,000
Goodwill			$ 205,000,000			$ 205,000,000