Goodwill and Other Intangible Assets (Tables)

12 Months Ended

Dec. 31, 2017

Acquired Finite-Lived Intangible Assets [Line Items]

Schedule of Acquired Finite-Lived Intangible Assets by Major Class [Table Text Block]

The following table presents the economic lives, acquisition date values, accumulated amortization and net carrying values for other intangible assets and goodwill, by company:

$ in millions	Weighted Average Economic  life (in years)	December 31, 2017						December 31, 2016
		Acquisition date fair value		Accumulated amortization		Net carrying value		Acquisition date fair value		Accumulated amortization		Net carrying value
Goodwill:
MediaAlpha	N/A	$	18.3	$	—	$	18.3	$	18.3	$	—	$	18.3
Buzzmove	N/A	7.6		—		7.6		7.6		—		7.6
Total goodwill		25.9		—		25.9		25.9		—		25.9
Other intangible assets:
MediaAlpha
Customer relationships	8	36.6		10.2		26.4		10.0		6.2		3.8
Information technology	5	33.3		24.3		9.0		32.4		17.9		14.5
Subtotal		69.9		34.5		35.4		42.4		24.1		18.3
Buzzmove
Trademark	7	.6		.1		.5		.6		.1		.5
Information technology	5	.5		.2		.3		.5		—		.5
Subtotal		1.1		.3		.8		1.1		.1		1.0
Total other intangible assets		71.0		34.8		36.2		43.5		24.2		19.3
Total goodwill and other    intangible assets		$	96.9	$	34.8	$	62.1	$	69.4	$	24.2	$	45.2

Schedule of Intangible Assets and Goodwill

The following table presents goodwill and other intangible assets as of December 31, 2017 and December 31, 2016:

Millions	December 31, 2017			December 31, 2016
Goodwill:
MediaAlpha	$	18.3		$	18.3
Buzzmove	7.6			7.6
Total goodwill	25.9			25.9
Other intangible assets:
MediaAlpha	35.4			18.3
Buzzmove	.8			1.0
Total other intangible assets	36.2			19.3
Total goodwill and other intangible assets	62.1			45.2
Goodwill and other intangible assets held for sale	—			1.2
Goodwill and other intangible assets attributed to non-controlling interests	(21.1		)	(17.1		)
Goodwill and other intangible assets included in White Mountains’s common shareholders' equity	$	41.0		$	29.3

Schedule of Goodwill and Intangible Assets Rollforward

The following table presents the change in goodwill and other intangible assets:

	December 31,
	2017					2016
Millions	Goodwill		Other intangible assets			Goodwill			Other intangible assets
Beginning balance	$	25.9	$	19.3		$	18.6		$	26.9
Add: Star & Shield amounts held for sale at beginning of the period(1)	—		—			—			.4
Acquisitions of businesses and asset groups (2)			27.6			7.6			5.0
Wobi write-off	—		—			(.3		)	(2.5		)
Amortization, including foreign currency translation	—		(10.7		)	—			(10.5		)
Ending balance	$	25.9	$	36.2		$	25.9		$	19.3

Schedule of Finite-Lived Intangible Assets, Future Amortization Expense

White Mountains expects to recognize amortization expense in each of the next five years as the following table presents:

Millions	Amortization expense
2018	$	10.2
2019	5.0
2020	3.2
2021	2.9
2022	2.8
Total	$	24.1