SCHEDULE II CONDENSED FINANCIAL INFORMATION OF REGISTRANT PARENT COMPANY ONLY (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
The Hanover Insurance Group [Member]
Supplementary Insurance Information By Segment [Line Items]
Investment assets transferred to the parent company to settle dividend balances	$ 98.6	$ 98.8	$ 166.0