Accumulated Other Comprehensive Income (Tables)

9 Months Ended

Sep. 30, 2024

Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]

Schedule of Components of Accumulated Other Comprehensive Income, Net of Tax

The following tables summarize those reclassification adjustments (net of taxes) for the periods indicated: 

	Three Months Ended September 30, 2024
	Foreign currency translation adjustment		Net unrealized losses on investments		Net unrealized gains on derivative transactions		Unamortized net losses on Pension Plans		Accumulated other comprehensive loss
Balance at June 30, 2024	$	(375.5)	$	(360.7)	$	4.4	$	(120.9)	$	(852.7)
Change in accumulated other comprehensive loss before reclassifications	15.2		193.8		3.2		—		212.2
Amounts reclassified from accumulated other comprehensive loss	—		15.9		(0.2)		(2.4)		13.3
Net current-period other comprehensive loss	15.2		209.7		3.0		(2.4)		225.5
Balance at September 30, 2024	$	(360.3)	$	(151.0)	$	7.4	$	(123.3)	$	(627.2)

	Three Months Ended September 30, 2023
	Foreign currency translation adjustment		Net unrealized losses on investments		Net unrealized gains on derivative transactions		Unamortized net losses on Pension Plans		Accumulated other comprehensive loss
Balance at June 30, 2023	$	(360.3)	$	(480.9)	$	12.0	$	(93.5)	$	(922.7)
Change in accumulated other comprehensive loss before reclassifications	(11.3)		(123.5)		(2.0)		(0.4)		(137.2)
Amounts reclassified from accumulated other comprehensive loss	—		10.6		0.8		(2.5)		8.9
Net current-period other comprehensive loss	(11.3)		(112.9)		(1.2)		(2.9)		(128.3)
Balance at September 30, 2023	$	(371.6)	$	(593.8)	$	10.8	$	(96.4)	$	(1,051.0)
	Nine Months Ended September 30, 2024
	Foreign currency translation adjustment		Net unrealized gains (losses) on investments		Net unrealized gains on derivative transactions		Unamortized net losses on Pension Plans		Accumulated other comprehensive loss
Balance at December 31, 2023	$	(351.9)	$	(305.5)	$	8.5	$	(116.1)	$	(765.0)
Change in accumulated other comprehensive loss before reclassifications	(8.4)		116.0		4.7		—		112.3
Amounts reclassified from accumulated other comprehensive loss	—		38.5		(5.8)		(7.2)		25.5
Net current-period other comprehensive loss	(8.4)		154.5		(1.1)		(7.2)		137.8
Balance at September 30, 2024	$	(360.3)	$	(151.0)	$	7.4	$	(123.3)	$	(627.2)
	Nine Months Ended September 30, 2023
	Foreign currency translation adjustment		Net unrealized gains on investments		Net unrealized gains on derivative transactions		Unamortized net losses on Pension Plans		Accumulated other comprehensive loss
Balance at December 31, 2022	$	(394.0)	$	(513.2)	$	9.8	$	(88.8)	$	(986.2)
Change in accumulated other comprehensive loss before reclassifications	22.4		(102.3)		1.4		(0.1)		(78.6)
Amounts reclassified from accumulated other comprehensive loss	—		21.7		(0.4)		(7.5)		13.8
Net current-period other comprehensive loss	22.4		(80.6)		1.0		(7.6)		(64.8)
Balance at September 30, 2023	$	(371.6)	$	(593.8)	$	10.8	$	(96.4)	$	(1,051.0)

Schedule of Reclassification out of Accumulated Other Comprehensive Income

The following tables summarize the reclassifications out of AOCI for the periods indicated:

Details about accumulated other comprehensive income components	Amount reclassified from accumulated other comprehensive income								Affected line item in the statement where net income is presented
	Three Months Ended September 30,				Nine Months Ended September 30,
	2024		2023		2024		2023
Net unrealized losses on investments	$	20.1	$	13.5	$	48.7	$	27.5	Net realized losses on investments and fair value changes to equity securities
	(4.2)		(2.9)		(10.2)		(5.8)		Provision for income taxes
	$	15.9	$	10.6	$	38.5	$	21.7	Net of tax
Net unrealized (gains) losses on derivative transactions related to:
Interest rate derivatives	$	(0.7)	$	(0.7)	$	(2.1)	$	(2.7)	Interest expense
Foreign exchange derivatives	0.4		1.7		(5.3)		2.1		Underwriting, selling, general and administrative expenses
	(0.3)		1.0		(7.4)		(0.6)
	0.1		(0.2)		1.6		0.2		Provision for income taxes
	$	(0.2)	$	0.8	$	(5.8)	$	(0.4)	Net of tax
Amortization of pension and postretirement unrecognized net periodic benefit cost:
Amortization of net loss	$	0.2	$	0.2	$	0.8	$	0.8	(1)
Amortization of prior service credit	(3.4)		(3.4)		(10.2)		(10.2)		(1)
	(3.2)		(3.2)		(9.4)		(9.4)
	0.8		0.7		2.2		1.9		Provision for income taxes
	$	(2.4)	$	(2.5)	$	(7.2)	$	(7.5)	Net of tax
Total reclassifications for the period	$	13.3	$	8.9	$	25.5	$	13.8	Net of tax

(1)These AOCI components are included in the computation of net periodic pension cost. For additional information, see Note 12.