Debt (Tables)

12 Months Ended

Dec. 31, 2023

Debt Disclosure [Abstract]

Schedule of Long-term Debt Instruments

Total amortized cost of Long-term Debt outstanding at December 31, 2023 and 2022 was:

(Dollars in Millions)	Dec 31, 2023		Dec 31, 2022
Senior Notes:
4.350% Senior Notes due February 15, 2025	$	449.6	$	449.3
2.400% Senior Notes due September 30, 2030	397.0		396.6
3.800% Senior Notes due February 23, 2032	396.0		395.5
5.875% Fixed-Rate Reset Junior Subordinated Debentures due 2062	146.6		145.5
Total Long-term Debt Outstanding	$	1,389.2	$	1,386.9