CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Assets
Common equity securities, at fair value	$ 561.5	$ 538.4
Other long-term investments	1,991.9	1,998.2
Goodwill and other intangible assets	736.6	370.6
Total assets	9,590.3	8,385.9
Liabilities
Debt	532.1	534.6
Total liabilities	4,699.7	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 2,565,733 and 2,560,452 shares	2.6	2.6
Paid-in surplus	551.9	548.7
Retained earnings	3,917.7	3,690.8
Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax	(1.8)	(1.6)
Accumulated other comprehensive income (loss), after-tax:
Total White Mountains’s common shareholders’ equity	4,470.4	4,240.5
Noncontrolling interests	420.2	321.1
Total equity	4,890.6	4,561.6
Total liabilities and equity	9,590.3	8,385.9
Other Operations
Assets
Fixed maturity investments, at fair value	267.4	230.2
Common equity securities, at fair value	151.6	137.8
Investment in MediaAlpha, at fair value	465.6	254.9
Short-term investments, at fair value	126.1	425.2
Other long-term investments	617.0	661.0
Total investments	1,627.7	1,709.1
Cash	23.0	23.8
Goodwill and other intangible assets	68.7	69.8
Other assets	81.7	73.2
Total assets	1,801.1	1,875.9
Liabilities
Debt	25.9	28.4
Accrued incentive compensation	47.6	87.7
Other liabilities	41.8	25.0
Total liabilities	115.3	141.1
P&C Insurance and Reinsurance (Ark/WM Outrigger)
Liabilities
Loss and loss adjustment expense reserves	1,744.5	1,605.1
P&C Insurance and Reinsurance (Ark/WM Outrigger) | Operating Segments
Assets
Fixed maturity investments, at fair value	946.9	866.8
Common equity securities, at fair value	409.9	400.6
Short-term investments, at fair value	835.3	962.8
Other long-term investments	485.0	440.9
Total investments	2,677.1	2,671.1
Cash	129.1	90.5
Reinsurance recoverables	695.0	442.0
Insurance premiums receivable	1,001.5	612.2
Deferred acquisition costs	213.3	145.3
Goodwill and other intangible assets	292.5	292.5
Other assets	140.9	125.0
Total assets	5,149.4	4,378.6
Liabilities
Loss and loss adjustment expense reserves	1,744.5	1,605.1
Unearned insurance premiums	1,234.7	743.6
Debt	155.4	185.5
Reinsurance payable	262.5	81.1
Contingent consideration	94.0	94.0
Other liabilities	190.1	166.8
Total liabilities	3,681.2	2,876.1
Financial Guarantee (HG Global/BAM) | Operating Segments
Assets
Fixed maturity investments, at fair value	1,015.7	1,012.3
Short-term investments, at fair value	54.7	70.6
Total investments	1,070.4	1,082.9
Cash	4.7	6.7
Insurance premiums receivable	5.8	5.5
Deferred acquisition costs	40.9	40.1
Other assets	36.8	36.8
Total assets	1,158.6	1,172.0
Liabilities
Unearned insurance premiums	328.5	325.8
Debt	147.0	146.9
Accrued incentive compensation	11.9	27.2
Other liabilities	31.9	31.8
Total liabilities	519.3	531.7
Asset Management (Kudu) | Operating Segments
Assets
Short-term investments, at fair value	19.8	29.3
Other long-term investments	889.9	896.3
Total investments	909.7	925.6
Cash	6.5	1.4
Accrued investment income	22.1	17.6
Goodwill and other intangible assets	8.2	8.3
Other assets	6.6	6.5
Total assets	953.1	959.4
Liabilities
Debt	203.8	203.8
Other liabilities	61.8	71.6
Total liabilities	265.6	275.4
P&C Insurance Distribution (Bamboo) | Operating Segments
Assets
Fixed maturity investments, at fair value	24.6	0.0
Short-term investments, at fair value	18.6	0.0
Total investments	43.2	0.0
Cash	62.0	0.0
Premiums, commissions and fees receivable	43.3	0.0
Goodwill and other intangible assets	367.2	0.0
Other assets	12.4	0.0
Total assets	528.1	0.0
Liabilities
Loss and loss adjustment expense reserves	12.3	0.0
Unearned insurance premiums	25.7	0.0
Premiums and commissions payable	61.7	0.0
Other liabilities	18.6	0.0
Total liabilities	$ 118.3	$ 0.0