Summary of Significant Accounting Policies - Additional Information (Details)		3 Months Ended	12 Months Ended
		Dec. 31, 2023 USD ($)	Dec. 31, 2024 USD ($) Segment	Dec. 31, 2023 USD ($) Segment	Dec. 31, 2022 USD ($)
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Number of reportable segments | Segment			3	4
Change in accounting principle, accounting standards update, adopted			true
Amount recorded additional gain from settlement of contingent payments			$ 29,000,000
Change in accounting principle, accounting standards update, description			ASU 2023-07
Average annual earnings, operating profit earned period maximum			3 years
Accumulated impairment losses			$ 0
Goodwill impairment loss			0	$ 0	$ 0
Gain on Disposition of Assets			31,000,000	143,000,000	$ 5,000,000
Carrying value of fixed-rate borrowings		$ 2,740,000,000	2,839,000,000	2,740,000,000
Long-term Debt, Fair Value		$ 2,488,000,000	2,602,000,000	$ 2,488,000,000
Revolving and term loan			1,006,000,000
Amount written off as uncollectable from reinsurance carriers			$ 0
Purchased Customer Accounts and Other
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Finite-Lived Intangible Asset, Useful Life	[1]	15 years	15 years	15 years
Third-party Claims Administration and Adjusting Services Businesses | Services
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Gains recognized on sales of businesses		$ 135,000,000
Percentage of business sold		50.00%
Minimum
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Property, Plant and Equipment, Useful Life			3 years
Maximum
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Property, Plant and Equipment, Useful Life			40 years

[1] Weighted average life calculated as of the date of acquisition.