Goodwill and Other Intangible Assets (Tables)

12 Months Ended

Dec. 31, 2024

Goodwill and Intangible Assets Disclosure [Abstract]

Schedule of intangible assets and goodwill

The following table presents the economic life, acquisition date fair value, accumulated amortization and net carrying value for other intangible assets and goodwill as of December 31, 2024 and 2023:

$ in Millions	Weighted Average Economic  Life (in years)	December 31, 2024						December 31, 2023
		Acquisition Date Fair Value		Accumulated Amortization		Net Carrying Value		Acquisition Date Fair Value		Accumulated Amortization		Net Carrying Value
Goodwill:
Ark	N/A	$	116.8	$	—	$	116.8	$	116.8	$	—	$	116.8
Kudu	N/A	7.6		—		7.6		7.6		—		7.6
Bamboo	N/A	270.4		—		270.4		—		—		—
Other Operations	N/A	44.4		—		44.4		44.4		—		44.4
Total goodwill		439.2		—		439.2		168.8		—		168.8
Other intangible assets:
Ark
Underwriting capacity	N/A	175.7		—		175.7		175.7		—		175.7
Kudu
Trade names	7.0	2.2		1.8		.4		2.2		1.5		.7
Bamboo
Trade names	10.0	23.5		2.3		21.2		—		—		—
Agency relationships	6.0	72.4		12.1		60.3		—		—		—
Developed technology	3.0	4.7		1.6		3.1		—		—		—
Other	0.3	.4		.4		—		—		—		—
Subtotal		101.0		16.4		84.6		—		—		—
Other Operations
Trade names	13.3	13.3		5.6		7.7		13.3		4.1		9.2
Customer relationships	11.0	24.8		13.6		11.2		24.8		10.3		14.5
Other	11.8	3.1		1.6		1.5		2.8		1.1		1.7
Subtotal		41.2		20.8		20.4		40.9		15.5		25.4
Total other intangible assets		320.1		39.0		281.1		218.8		17.0		201.8
Total goodwill and other intangible assets		$	759.3	$	39.0	$	720.3	$	387.6	$	17.0	$	370.6

The following table presents the change in goodwill and other intangible assets for the years ended December 31, 2024 and 2023:

	December 31, 2024						December 31, 2023
Millions	Goodwill		Other Intangible Assets		Total Goodwill and Other Intangible Assets		Goodwill		Other Intangible Assets		Total Goodwill and Other Intangible Assets
Beginning balance	$	168.8	$	201.8	$	370.6	$	176.5	$	215.9	$	392.4
Acquisitions of businesses (1)	270.4		101.0		371.4		—		—		—
Acquisitions of intangible assets (2)	—		.3		.3		—		—		—
Dispositions (2)	—		—		—		(6.7)		(6.9)		(13.6)
Measurement period adjustments (3)	—		—		—		(1.0)		—		(1.0)
Amortization	—		(22.0)		(22.0)		—		(7.2)		(7.2)
Ending balance	$	439.2	$	281.1	$	720.3	$	168.8	$	201.8	$	370.6

(1) Relates to the Bamboo Transaction. See Note 2 — “Significant Transactions.”

(2) Relates to acquisitions and dispositions within Other Operations.

(3) Measurement period adjustments relate to updated information about acquisition date fair values of assets acquired and liabilities assumed. Adjustments relate to acquisitions of certain consolidated Other Operating Businesses.

Schedule of finite-lived intangible assets, future amortization expense

The following table presents a schedule of White Mountains’s future amortization expense as of December 31, 2024:

Millions	Amortization Expense
2025	$	20.8
2026	20.1
2027	17.9
2028	16.9
2029	16.4
2030 and years after	13.3
Total (1)	$	105.4

(1) Excludes Ark’s indefinite-lived intangible assets of $175.7.