Acquisition of Businesses - Allocation of purchase price of subsidiary (Details) - USD ($) $ in Millions		9 Months Ended
	Jul. 03, 2023	Sep. 30, 2023	Sep. 30, 2022
Business Acquisition [Line Items]
Payments to acquire subsidiaries		$ 234	$ 10
Crop Risk Services
Business Acquisition [Line Items]
Payments to acquire subsidiaries	$ 234
Tangible assets acquired:
Cash and cash equivalents	26
Agents’ balances and premiums receivable	164
Other assets	3
Total tangible assets acquired	193
Liabilities acquired:
Other liabilities	169
Total liabilities acquired	169
Net tangible assets acquired, at fair value	24
Excess purchase price over net tangible assets acquired	210
Deferred tax asset acquired	1
Goodwill recorded	85
Crop Risk Services | Customer relationships
Liabilities acquired:
Intangible assets acquired	$ 124