Deferred Acquisition Costs (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Beginning balance	$ 10,380.0	$ 10,138.5	$ 10,187.6	$ 9,992.8
Costs deferred	1,235.6	926.3	3,443.6	3,195.8
Amortization	(1,036.0)	(933.7)	(3,051.6)	(3,057.5)
Ending balance	$ 10,579.6	$ 10,131.1	$ 10,579.6	$ 10,131.1

Amount of amortization expense (reversal of expense) for deferred policy acquisition costs.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 230
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 28
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482740/230-10-45-28

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 944
-SubTopic 605
-Name Accounting Standards Codification
-Section 55
-Paragraph 14
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477548/944-605-55-14

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Topic 944
-SubTopic 605
-Name Accounting Standards Codification
-Section 55
-Paragraph 11
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477548/944-605-55-11

Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479868/944-20-45-2

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 40
-Name Accounting Standards Codification
-Section 65
-Paragraph 2
-Subparagraph (g)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480016/944-40-65-2

Reference 6: http://www.xbrl.org/2003/role/exampleRef
-Topic 944
-SubTopic 30
-Name Accounting Standards Codification
-Section 55
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479401/944-30-55-2

Reference 7: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 944
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479432/944-30-50-2

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 2B
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479432/944-30-50-2B

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(7)(a))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477250/944-220-S99-1

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479432/944-30-50-1

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 22
-Subparagraph (u)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147476148/220-40-50-22

+ Details

- Definition

Amount of deferred policy acquisition cost capitalized on contract remaining in force.

+ References + Details