|**Employee Retirement Benefits**                      | 6 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|----------------------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|
|**Retirement Benefits [Abstract]**                    |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|Employee Retirement Benefits                          | Employee Retirement BenefitsThe following summarizes the components of net periodic benefit for our qualified and supplemental pension plans:(Dollars in millions)Three months ended June 30,Six months ended June 30,2023202220232022Service cost$2$3$3$5Non-service (benefit) costs:Interest cost3265Expected return on plan assets(5)(5)(10)(11)Amortization of actuarial loss and prior service cost(1)—(2)—Other——(5)—Total non-service benefit(3)(3)(11)(6)Net periodic benefit$(1)$—$(8)$(1)See our 2022 Annual Report on Form 10-K, Item 8, Note 13, Employee Retirement Benefits, Page 163, for information on our retirement benefits. The net periodic benefit is allocated in the same proportion primarily to the underwriting, acquisition and insurance expenses line item with the remainder allocated to the insurance losses and contract holders' benefits line item on the condensed consolidated statements of income for both 2023 and 2022.We made matching contributions totaling $6 million to our 401(k) and Top Hat savings plans during both the second quarter of 2023 and 2022 and contributions of $14 million for both the first half of 2023 and 2022.We made no contributions to our qualified pension plan during the first six months of 2023.
|                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|(Dollars in millions)                                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|Service cost                                          |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|Non-service (benefit) costs:                          |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|Interest cost                                         |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|Expected return on plan assets                        |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|Amortization of actuarial loss and prior service cost |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|Other                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|Total non-service benefit                             |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|Net periodic benefit                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   

X- ReferencesNo definition available.
+ Details**Name:**
us-gaap_CompensationAndRetirementDisclosureAbstract**Namespace Prefix:**
us-gaap_**Data Type:**
xbrli:stringItemType**Balance Type:**
na**Period Type:**
duration X- DefinitionThe entire disclosure for retirement benefits.
+ ReferencesReference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 70 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480794/715-70-50-1Reference 2: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 17 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480482/715-20-55-17Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(03) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (d)(i) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (q) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (l) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1Reference 7: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -Name Accounting Standards Codification -Publisher FASB -URI https://asc.fasb.org//715/tableOfContentReference 8: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (d)(iii) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1Reference 9: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (o) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1Reference 10: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (p) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1Reference 11: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (r)(1) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1Reference 12: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (r)(2) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1Reference 13: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section S99 -Paragraph 2 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480126/715-20-S99-2Reference 14: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 60 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480266/715-60-50-3
+ Details**Name:**
us-gaap_PensionAndOtherPostretirementBenefitsDisclosureTextBlock**Namespace Prefix:**
us-gaap_**Data Type:**
dtr-types:textBlockItemType**Balance Type:**
na**Period Type:**
duration