CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Assets
Common equity securities, at fair value	$ 655.4	$ 538.4
Other long-term investments	2,071.1	1,998.2
Goodwill and other intangible assets	725.7	370.6
Total assets	10,337.5	8,385.9
Liabilities
Debt	544.9	564.6
Total liabilities	5,077.7	3,824.3
White Mountains’s common shareholders’ equity
White Mountains’s common shares at $1 par value per share—authorized 50,000,000 shares; issued and outstanding 2,568,148 and 2,560,452 shares	2.6	2.6
Paid-in surplus	560.7	548.7
Retained earnings	4,048.3	3,690.8
Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax	(1.0)	(1.6)
Accumulated other comprehensive income (loss), after-tax:
Total White Mountains’s common shareholders’ equity	4,610.6	4,240.5
Noncontrolling interests	649.2	321.1
Total equity	5,259.8	4,561.6
Total liabilities and equity	10,337.5	8,385.9
Other Operations
Assets
Fixed maturity investments, at fair value	286.1	230.2
Common equity securities, at fair value	219.8	137.8
Investment in MediaAlpha, at fair value	323.4	254.9
Short-term investments, at fair value	241.7	425.2
Other long-term investments	589.5	661.0
Total investments	1,660.5	1,709.1
Cash	28.2	23.8
Insurance premiums receivable	34.3	0.0
Goodwill and other intangible assets	66.2	69.8
Other assets	74.2	73.2
Total assets	1,863.4	1,875.9
Liabilities
Loss and loss adjustment expense reserves	8.1	0.0
Unearned insurance premiums	28.5	0.0
Debt	22.3	28.4
Accrued incentive compensation	64.5	87.7
Other liabilities	33.8	25.0
Total liabilities	157.2	141.1
P&C Insurance and Reinsurance (Ark/WM Outrigger)
Liabilities
Loss and loss adjustment expense reserves	2,133.0	1,605.1
P&C Insurance and Reinsurance (Ark/WM Outrigger) | Operating Segments
Assets
Fixed maturity investments, at fair value	1,461.2	866.8
Common equity securities, at fair value	435.6	400.6
Short-term investments, at fair value	579.1	962.8
Other long-term investments	544.8	440.9
Total investments	3,020.7	2,671.1
Cash	148.8	90.5
Reinsurance recoverables	748.0	442.0
Insurance premiums receivable	993.0	612.2
Deferred acquisition costs	199.7	145.3
Goodwill and other intangible assets	292.5	292.5
Other assets	175.8	125.0
Total assets	5,578.5	4,378.6
Liabilities
Loss and loss adjustment expense reserves	2,133.0	1,605.1
Unearned insurance premiums	1,149.8	743.6
Debt	156.8	185.5
Reinsurance payable	230.2	81.1
Contingent consideration	141.5	94.0
Other liabilities	188.9	166.8
Total liabilities	4,000.2	2,876.1
Financial Guarantee (HG Global) | Operating Segments
Assets
Fixed maturity investments, at fair value	636.1	1,012.3
Short-term investments, at fair value	34.6	70.6
Total investments	670.7	1,082.9
Cash	1.2	6.7
BAM Surplus Notes, at fair value	411.1	0.0
Insurance premiums receivable	7.9	5.5
Deferred acquisition costs	83.2	40.1
Other assets	27.8	36.8
Total assets	1,201.9	1,172.0
Liabilities
Unearned insurance premiums	287.0	325.8
Debt	147.3	146.9
Other liabilities	19.6	59.0
Total liabilities	453.9	531.7
Asset Management (Kudu) | Operating Segments
Assets
Short-term investments, at fair value	20.3	29.3
Other long-term investments	936.8	896.3
Total investments	957.1	925.6
Cash	76.7	1.4
Accrued investment income	15.7	17.6
Goodwill and other intangible assets	8.0	8.3
Other assets	36.6	6.5
Total assets	1,094.1	959.4
Liabilities
Debt	218.5	203.8
Other liabilities	75.9	71.6
Total liabilities	294.4	275.4
P&C Insurance Distribution (Bamboo) | Operating Segments
Assets
Fixed maturity investments, at fair value	38.9	0.0
Short-term investments, at fair value	14.6	0.0
Total investments	53.5	0.0
Cash	91.1	0.0
Premiums, commissions and fees receivable	72.7	0.0
Goodwill and other intangible assets	359.0	0.0
Other assets	23.3	0.0
Total assets	599.6	0.0
Liabilities
Loss and loss adjustment expense reserves	17.7	0.0
Unearned insurance premiums	29.9	0.0
Premiums and commissions payable	93.7	0.0
Other liabilities	30.7	0.0
Total liabilities	$ 172.0	$ 0.0