CNA Financial (CNA) 10-K 13 Feb 19 2018 FY Annual report Financial data

Document and Entity Information

Document and Entity Information Document - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Feb. 08, 2019	Jun. 29, 2018
Document and Entity Information [Abstract]
Entity Registrant Name	CNA FINANCIAL CORP
Entity Central Index Key	21,175
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-K
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Common Stock, Shares Outstanding (in shares)		271,469,504
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Public Float			$ 1,295

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues
Net earned premiums	$ 7,312	$ 6,988	$ 6,924
Net investment income	1,817	2,034	1,988
Net realized investment (losses) gains:
Other-than-temporary impairment losses	(21)	(14)	(81)
Other net realized investment (losses) gains	(31)	107	131
Net realized investment gains (losses)	(52)	93	50
Non-insurance warranty revenue	1,007	390	361
Other revenues	50	37	43
Total revenues	10,134	9,542	9,366
Claims, Benefits and Expenses
Insurance claims and policyholders’ benefits	5,572	5,310	5,283
Amortization of deferred acquisition costs	1,335	1,233	1,235
Non-insurance warranty expense	923	299	271
Other operating expenses	1,202	1,229	1,281
Interest	138	161	159
Total claims, benefits and expenses	9,170	8,232	8,229
Income before income tax	964	1,310	1,137
Income tax expense	(151)	(411)	(278)
Net income	$ 813	$ 899	$ 859
Basic earnings per share
Basic earnings per share (in usd per share)	$ 2.99	$ 3.32	$ 3.18
Diluted earnings per share
Diluted earnings per share (in usd per share)	$ 2.98	$ 3.30	$ 3.17
Weighted Average Outstanding Common Stock and Common Stock Equivalents
Basic (in shares)	271.5	271.1	270.4
Diluted (in shares)	272.5	272.1	271.1

Consolidated Statements of Comp

Consolidated Statements of Comprehensive (Loss) Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Net income	$ 813	$ 899	$ 859
Other Comprehensive (Loss) Income, Net of Tax
Net unrealized gains on investments	(812)	103	255
Foreign currency translation adjustment	(82)	100	(114)
Pension and postretirement benefits	0	2	1
Other comprehensive (loss) income, net of tax	(894)	205	142
Total comprehensive (loss) income	(81)	1,104	1,001
Net unrealized gains on investments with other-than-temporary impairments
Other Comprehensive (Loss) Income, Net of Tax
Net unrealized gains on investments	14	5	(3)
Net unrealized gains on other investments
Other Comprehensive (Loss) Income, Net of Tax
Net unrealized gains on investments	$ (798)	$ 108	$ 252

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Investments:
Fixed maturity securities at fair value (amortized cost of $38,085 and $38,215)	$ 39,546	$ 41,487
Equity securities at fair value (cost of $844 and $659)	780	695
Limited partnership investments	1,982	2,369
Other invested assets	53	44
Mortgage loans	839	839
Short term investments	1,286	1,436
Total investments	44,486	46,870
Cash	310	355
Reinsurance receivables (less allowance for uncollectible receivables of $29 and $29)	4,426	4,261
Insurance receivables (less allowance for uncollectible receivables of $42 and $44)	2,323	2,292
Accrued investment income	391	411
Deferred acquisition costs	633	634
Deferred income taxes	392	137
Property and equipment at cost (less accumulated depreciation of $216 and $274)	324	326
Goodwill	146	148
Deferred non-insurance warranty acquisition expense	2,513	212
Other assets (includes $8 and $- due from Loews Corporation)	1,208	921
Total assets	57,152	56,567
Insurance reserves:
Claim and claim adjustment expenses	21,984	22,004
Unearned premiums	4,183	4,029
Future policy benefits	10,597	11,179
Short term debt	0	150
Long term debt	2,680	2,708
Deferred non-insurance warranty revenue	3,402	972
Other liabilities (includes $23 and $143 due to Loews Corporation)	3,089	3,281
Total liabilities	45,935	44,323
Commitments and contingencies (Notes B, F and L)
Stockholders' Equity
Common stock ($2.50 par value; 500,000,000 shares authorized; 273,040,243 shares issued; 271,456,978 and 271,205,390 shares outstanding)	683	683
Additional paid-in capital	2,192	2,175
Retained earnings	9,277	9,414
Accumulated other comprehensive (loss) income	(878)	32
Treasury stock (1,583,265 and 1,834,853 shares), at cost	(57)	(60)
Total stockholders’ equity	11,217	12,244
Total liabilities and stockholders' equity	$ 57,152	$ 56,567

Consolidated Balance Sheets - (

Consolidated Balance Sheets - (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Fixed maturities securities at amortized cost	$ 38,085,000	$ 38,215,000
Equity securities at cost	844,000
Equity securities at cost		659,000
Allowance for uncollectible reinsurance	29,000	29,000
Allowance for uncollectible insurance receivables	42,000	44,000
Accumulated depreciation on property and equipment	216,000	274,000
Due to related parties	23,000	143,000
Due from related parties	$ 8,000	$ 0
Common stock, par value (in usd per share)	$ 2.50	$ 2.50
Common stock, shares authorized (in shares)	500,000,000	500,000,000
Common stock, shares issued (in shares)	273,040,243	273,040,243
Common stock, shares outstanding (in shares)	271,456,978	271,205,390
Treasury stock, shares (in shares)	1,583,265	1,834,853

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash Flows from Operating Activities
Net income	$ 813	$ 899	$ 859
Adjustments to reconcile net income to net cash flows provided by operating activities:
Deferred income tax (benefit) expense	(20)	168	136
Trading portfolio activity	0	9	(9)
Net realized investment losses (gains)	52	(93)	(50)
Equity method investees	330	84	238
Net amortization of investments	(70)	(40)	(27)
Depreciation and amortization	79	88	77
Changes in:
Receivables, net	(229)	92	(130)
Accrued investment income	19	(4)	(3)
Deferred acquisition costs	(6)	(24)	(8)
Insurance reserves	482	22	237
Other assets	(192)	(158)	(95)
Other liabilities	(98)	173	162
Other, net	67	38	29
Total adjustments	414	355	557
Net cash flows provided by operating activities	1,227	1,254	1,416
Dispositions:
Fixed maturity securities - sales	8,408	5,438	5,328
Fixed maturity securities - maturities, calls and redemptions	2,370	3,641	3,219
Equity securities	89	46	81
Limited partnerships	343	192	290
Mortgage loans	128	26	207
Purchases:
Fixed maturity securities	(10,785)	(9,065)	(9,827)
Equity securities	(258)	(166)	0
Limited partnerships	(419)	(171)	(252)
Mortgage loans	(128)	(274)	(120)
Change in other investments	(12)	(3)	7
Change in short term investments	168	(6)	258
Purchases of property and equipment	(99)	(102)	(146)
Disposals of property and equipment	0	0	107
Other, net	18	20	2
Net cash flows used by investing activities	(177)	(424)	(846)
Cash Flows from Financing Activities
Dividends paid to common stockholders	(896)	(842)	(813)
Proceeds from the issuance of debt	0	496	498
Repayment of debt	(180)	(391)	(358)
Other, net	(9)	(18)	0
Net cash flows used by financing activities	(1,085)	(755)	(673)
Effect of foreign exchange rate changes on cash	(10)	9	(13)
Net change in cash	(45)	84	(116)
Cash, beginning of year	355	271	387
Cash, end of year	$ 310	$ 355	$ 271

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) $ in Millions	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive (Loss) Income	Treasury Stock	Previously ReportedRetained Earnings	Previously ReportedAccumulated Other Comprehensive (Loss) Income
Total stockholder's equity at beginning of period at Dec. 31, 2015		$ 683	$ 2,153			$ (78)	$ 9,313	$ (315)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation			20			5
Dividends to common stockholders ($3.30, $3.10, and $3.00 per share)				$ (813)
Net income	$ 859			859
Other comprehensive (loss) income	142				$ 142
Total stockholder's equity at end of period at Dec. 31, 2016	11,969	683	2,173	9,359	(173)	(73)	9,359	(173)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation			2			13
Dividends to common stockholders ($3.30, $3.10, and $3.00 per share)				(844)
Net income	899			899
Other comprehensive (loss) income	205				205
Total stockholder's equity at end of period at Dec. 31, 2017	12,244	683	2,175	9,414	32	(60)	$ 9,414	$ 32
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation			17			3
Dividends to common stockholders ($3.30, $3.10, and $3.00 per share)				(900)
Net income	813			813
Other comprehensive (loss) income	(894)				(894)
Total stockholder's equity at end of period at Dec. 31, 2018	$ 11,217	$ 683	$ 2,192	$ 9,277	$ (878)	$ (57)

Consolidated Statements of St_2

Consolidated Statements of Stockholders' Equity - (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Stockholders' Equity [Abstract]
Dividends declared per share (usd per share)	$ 3.30	$ 3.10	$ 3

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Basis of Presentation The Consolidated Financial Statements include the accounts of CNA Financial Corporation (CNAF) and its subsidiaries. Collectively, CNAF and its subsidiaries are referred to as CNA or the Company. Loews Corporation (Loews) owned approximately 89% of the outstanding common stock of CNAF as of December 31, 2018 . The accompanying Consolidated Financial Statements have been prepared in conformity with GAAP. Intercompany amounts have been eliminated. The preparation of Consolidated Financial Statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the Consolidated Financial Statements and the reported amounts of revenues and expenses during the reporting period. Actual results may differ from those estimates. Recently Adopted Accounting Standards Updates (ASU) ASU 2014-09: In May 2014, the FASB issued ASU No. 2014-09, Revenue Recognition (Topic 606) : Revenue from Contracts with Customers . The standard excludes from its scope the accounting for insurance contracts, financial instruments, and certain other agreements that are governed under other GAAP guidance, but the standard does apply to certain of the Company's warranty products and services. The updated guidance requires an entity to recognize revenue as performance obligations are met, in an amount that reflects the consideration the entity is entitled to receive for the transfer of the promised goods or services. On January 1, 2018, the Company adopted the updated guidance using the modified retrospective method applied to all contracts which were not completed as of the date of adoption, with the cumulative effect recognized as an adjustment to the opening balance of Retained earnings. Prior period amounts have not been adjusted and continue to be reported in accordance with the previous accounting guidance. Under the new guidance, revenue on warranty products and services is recognized more slowly as compared to the historic revenue recognition pattern. In addition, for warranty products where the Company acts as the principal in the transaction, Non-insurance warranty revenue and Non-insurance warranty expense are increased to reflect the gross amount paid by consumers, including the retail seller’s markup which is considered a commission to the Company's agent. This gross-up of revenue and expense also resulted in an increase to Deferred non-insurance warranty acquisition expense and Deferred non-insurance warranty revenue on the Company's Consolidated Balance Sheets as the revenue and expense are recognized over the actuarially determined expected claims emergence pattern. The cumulative effect changes to the Consolidated Balance Sheet for the adoption of the updated guidance on January 1, 2018 were as follows: (In millions) Balance as of December 31, 2017 Adjustments Due to Adoption of Topic 606 Balance as of January 1, 2018 Deferred non-insurance warranty acquisition expense $ 212 $ 1,882 $ 2,094 Deferred non-insurance warranty revenue 972 1,969 2,941 Deferred income taxes 137 21 158 Retained earnings 9,414 (66 ) 9,348 The impact of adoption on the Consolidated Statements of Operations and Balance Sheet was as follows: Year ended December 31, 2018 Prior to Adoption Effect of Adoption As Reported (In millions) Statement of operations: Non-insurance warranty revenue $ 420 $ 587 $ 1,007 Total revenues 9,547 587 10,134 Non-insurance warranty expense 328 595 923 Total claims, benefits and expenses 8,575 595 9,170 Income before income tax 972 (8 ) 964 Income tax expense (153 ) 2 (151 ) Net income 819 (6 ) 813 Balance sheet (1) at December 31, 2018: Deferred non-insurance warranty acquisition expense $ 2,116 $ 397 $ 2,513 Deferred non-insurance warranty revenue 2,997 405 3,402 Deferred income taxes 390 2 392 Retained earnings 9,283 (6 ) 9,277 (1) The Prior to Adoption amounts presented in this table include the cumulative effect adjustment at adoption presented in the prior table. See Note R to the Consolidated Financial Statements for additional information regarding non-insurance revenues from contracts with customers. ASU 2016-01: In January 2016, the FASB issued ASU No. 2016-01, Financial Instruments - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities . The updated accounting guidance requires changes to the reporting model for financial instruments. The guidance primarily changes the model for equity securities by requiring changes in the fair value of equity securities (except those accounted for under the equity method of accounting, those without readily determinable fair values and those that result in consolidation of the investee) to be recognized through the income statement. The Company adopted the updated guidance on January 1, 2018 and recognized a cumulative effect adjustment that increased beginning Retained earnings by $28 million , net of tax. Prior period amounts have not been adjusted and continue to be reported in accordance with the previous accounting guidance. For the year ended December 31, 2018 , the Company recognized $74 million in pretax losses within Net realized investment gains (losses) for the change in fair value of non-redeemable preferred stock and $22 million in pretax losses within Net investment income for the change in fair value of common stock as a result of this change. For the year ended December 31, 2017 , there was a $32 million increase in the fair value of non-redeemable preferred stock and a less than $1 million increase in the fair value of common stock, both recognized in Other comprehensive income. For the year ended December 31, 2016 , there was a $6 million decrease in the fair value of non-redeemable preferred stock and a $4 million increase in the fair value of common stock, both recognized in Other comprehensive income. ASU 2017-07: In March 2017, the FASB issued ASU No. 2017-07, Compensation-Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost . The updated accounting guidance requires changes to the presentation of the components of net periodic benefit cost on the income statement by requiring service cost to be presented with other employee compensation costs and other components of net periodic pension cost to be presented outside of any subtotal of operating income. The ASU also stipulates that only the service cost component of net benefit cost is eligible for capitalization. The Company adopted the updated guidance effective January 1, 2018. The guidance was applied on a prospective basis for capitalization of service costs and on a retrospective basis for the presentation of the service cost and other components of net periodic benefit costs in the Company's Consolidated Statements of Operations and in its disclosures. The Company utilized the practical expedient allowing amounts previously disclosed in its Benefit Plans footnote to be used as the estimation basis for prior comparative periods. The Company expanded the related footnote disclosure, Note I to the Consolidated Financial Statements, to disclose the amount of service cost and non-service cost components of net periodic benefit cost and the line items in the Consolidated Statements of Operations in which such amounts are reported. The change limiting the costs eligible for capitalization is not material to the Company’s results of operations or financial position. ASU 2018-02: In February 2018, the FASB issued ASU No. 2018-02, Income Statement - Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income. GAAP requires the remeasurement of deferred tax assets and liabilities due to a change in the tax rate to be included in Net income, even if the related income tax effects were originally recognized in Accumulated other comprehensive income (AOCI). The ASU allows a reclassification from AOCI to Retained earnings for stranded tax effects resulting from the new U.S. Federal corporate income tax rate enacted on December 22, 2017. The Company early adopted the updated guidance effective January 1, 2018 and elected to reclassify the stranded income tax effects relating to the reduction in the Federal corporate income tax rate from AOCI to Retained earnings at the beginning of the period of adoption. The net impact of the accounting change resulted in a $12 million increase in AOCI and a corresponding decrease in Retained earnings. The $12 million increase in AOCI is comprised of a $142 million increase in net unrealized gains (losses) on investments partially offset by a $130 million decrease in unrecognized pension and postretirement benefits. The Company releases tax effects from AOCI utilizing the security-by-security approach for Net unrealized gains (losses) on investments with Other-than-temporary impairment (OTTI) losses and Net unrealized gains (losses) on other investments. For Pension and postretirement benefits, tax effects from AOCI are released at enacted tax rates based on the pre-tax adjustments to pension liabilities or assets recognized within OCI. ASU 2018-13: In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820) Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement. The updated accounting guidance requires changes to the disclosures for fair value measurement by adding, removing and modifying disclosures. This guidance is effective for fiscal years beginning after December 15, 2019, including interim periods therein and early adoption is permitted. As of September 30, 2018, the Company adopted the updated guidance and added disclosures on changes in unrealized gains (losses) on Level 3 assets recognized in Other comprehensive income as well as the weighted average rate used to develop significant inputs utilized in the fair value measurements of Level 3 assets. The Company also eliminated disclosures on the amount of transfers between Level 1 and Level 2 assets and the policy for timing of transfers between Levels. ASU 2018-14: In August 2018, the FASB issued ASU No. 2018-14, Compensation -Retirement Benefits - Defined Benefit Plans - General (Subtopic 715-20) Disclosure Framework - Changes to the Disclosure Requirements for Defined Benefit Plans. The updated accounting guidance modifies the disclosure requirements for employers that sponsor defined benefit pension or other postretirement plans by removing, modifying and adding disclosures. The guidance is effective for annual periods ending after December 15, 2020, and early adoption is permitted. As of December 31, 2018, the Company adopted the updated accounting guidance by eliminating disclosures of the amounts in AOCI expected to be recognized as part of net periodic cost (benefit) during 2019. The Company also added disclosure of the interest crediting rate used in our defined benefit pension plan and a description of significant gains and losses affecting the benefit obligations for the periods presented. Accounting Standards Pending Adoption In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842): Accounting for Leases. The updated accounting guidance requires lessees to recognize on the balance sheet assets and liabilities for the rights and obligations created by the majority of leases, including those historically accounted for as operating leases. The guidance is effective for interim and annual periods beginning after December 15, 2018 and prescribes a modified retrospective transition method but allows entities to utilize a practical expedient and apply the guidance prospectively beginning with the adoption date. The Company has decided to utilize the practical expedient. The Company is finalizing its determination of the effect the updated guidance will have on its financial statements, but currently anticipates that asset and liabilities will increase approximately $230 million at the adoption date. The Company does not expect the impact of adoption to be material to the Company's results of operations. In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. The updated accounting guidance requires changes to the recognition of credit losses on financial instruments not accounted for at fair value through net income. The guidance is effective for interim and annual periods beginning after December 15, 2019. The guidance will be applied using a modified retrospective approach with the cumulative effect recognized as an adjustment to retained earnings. A prospective transition approach is required for debt securities that have recognized an other-than-temporary impairment prior to the effective date. The Company is currently evaluating the effect the guidance will have on the Company's financial statements, but expects the primary changes to be the use of the expected credit loss model for its mortgage loan portfolio, reinsurance and insurance receivables and other financing receivables and the use of the allowance method rather than the write-down method for credit losses within the available-for-sale fixed maturities portfolio. The expected credit loss model will require a financial asset to be presented at the net amount expected to be collected. The allowance method for available-for-sale debt securities will allow the Company to record reversals of credit losses if the estimate of credit losses declines. In August 2018, the FASB issued ASU 2018-12, Financial Services-Insurance (Topic 944): Targeted Improvements to the Accounting for Long-Duration Contracts . The updated accounting guidance requires changes to the measurement and disclosure of long-duration contracts. The guidance requires entities to annually update cash flow assumptions, including morbidity and persistency, and update discount rate assumptions quarterly using an upper-medium grade fixed-income instrument yield. The effect of changes in cash flow assumptions will be recorded in Net income and the effect of changes in discount rate assumptions will be recorded in Other comprehensive income. This guidance is effective for interim and annual periods beginning after December 15, 2020, and requires restatement of the prior periods presented. Early adoption is permitted. The Company is currently evaluating the method and timing of adoption and the effect the updated guidance will have on its financial statements. The annual updating of cash flow assumptions is expected to increase income statement volatility. The quarterly change in discount rate is expected to increase volatility in the Company’s stockholders' equity, but that will be somewhat mitigated because Shadow Adjustments are eliminated under the new guidance. While the requirements of the new guidance represent a material change from existing GAAP, the underlying economics of the business and related cash flows are unchanged. Insurance Operations Premiums: Insurance premiums on property and casualty insurance contracts are recognized in proportion to the underlying risk insured and are principally earned ratably over the term of the policies. Premiums on long term care contracts are earned ratably over the policy year in which they are due. The reserve for unearned premiums represents the portion of premiums written relating to the unexpired terms of coverage. Insurance receivables include balances due currently or in the future, including amounts due from insureds related to losses under high deductible policies, and are presented at unpaid balances, net of an allowance for uncollectible receivables. Amounts are considered past due based on policy payment terms. The allowance is determined based on periodic evaluations of aged receivables, historical business default data, management's experience and current economic conditions. Insurance receivables and any related allowance are written off after collection efforts are exhausted or a negotiated settlement is reached. Property and casualty contracts that are retrospectively rated contain provisions that result in an adjustment to the initial policy premium depending on the contract provisions and loss experience of the insured during the experience period. For such contracts, the Company estimates the amount of ultimate premiums that the Company may earn upon completion of the experience period and recognizes either an asset or a liability for the difference between the initial policy premium and the estimated ultimate premium. The Company adjusts such estimated ultimate premium amounts during the course of the experience period based on actual results to date. The resulting adjustment is recorded as either a reduction of or an increase to the earned premiums for the period. Claim and claim adjustment expense reserves: Claim and claim adjustment expense reserves, except reserves for structured settlements not associated with A&EP, workers' compensation lifetime claims and long term care claims, are not discounted and are based on i) case basis estimates for losses reported on direct business, adjusted in the aggregate for ultimate loss expectations; ii) estimates of incurred but not reported (IBNR) losses; iii) estimates of losses on assumed reinsurance; iv) estimates of future expenses to be incurred in the settlement of claims; v) estimates of salvage and subrogation recoveries and vi) estimates of amounts due from insureds related to losses under high deductible policies. Management considers current conditions and trends as well as past Company and industry experience in establishing these estimates. The effects of inflation, which can be significant, are implicitly considered in the reserving process and are part of the recorded reserve balance. Ceded claim and claim adjustment expense reserves are reported as a component of Reinsurance receivables on the Consolidated Balance Sheets. Claim and claim adjustment expense reserves are presented net of anticipated amounts due from insureds related to losses under deductible policies of $1.2 billion as of December 31, 2018 and 2017 . A significant portion of these amounts are supported by collateral. The Company has an allowance for uncollectible deductible amounts, which is presented as a component of the allowance for doubtful accounts included in Insurance receivables on the Consolidated Balance Sheets. Structured settlements have been negotiated for certain property and casualty insurance claims. Structured settlements are agreements to provide fixed periodic payments to claimants. The Company's obligations for structured settlements not funded by annuities are included in claim and claim adjustment expense reserves and carried at present values determined using interest rates ranging from to 5.5% to 8.0% as of December 31, 2018 and 2017 . As of December 31, 2018 and 2017 , the discounted reserves for unfunded structured settlements were $512 million and $527 million , net of discount of $760 million and $798 million . For the years ended December 31, 2018 , 2017 and 2016 , the amount of interest recognized on the discounted reserves of unfunded structured settlements was $40 million , $41 million and $42 million , respectively. This interest accretion is presented as a component of Insurance claims and policyholders’ benefits on the Consolidated Statements of Operations, but is excluded from the Company’s disclosure of prior year loss reserve development. Workers' compensation lifetime claim reserves are calculated using mortality assumptions determined through statutory regulation and economic factors. At December 31, 2018 and 2017 , workers' compensation lifetime claim reserves are discounted at a 3.5% interest rate. As of December 31, 2018 and 2017 , the discounted reserves for workers’ compensation lifetime claim reserves were $343 million and $346 million , net of discount of $168 million and $190 million . For the years ended December 31, 2018 , 2017 and 2016 , the amount of interest accretion recognized on the discounted reserves of workers’ compensation lifetime claim reserves was $16 million , $19 million and $17 million , respectively. This interest accretion is presented as a component of Insurance claims and policyholders' benefits on the Consolidated Statements of Operations, but is excluded from the Company's disclosure of prior year loss reserve development. Long term care claim reserves are calculated using mortality and morbidity assumptions based on Company and industry experience. Long term care claim reserves are discounted at an interest rate of 6.0% as of December 31, 2018 and 2017 . As of December 31, 2018 and 2017 , such discounted reserves totaled $2.6 billion and $2.4 billion , net of discount of $460 million and $446 million . Future policy benefit reserves: Future policy benefit reserves represent the active life reserves related to the Company's long term care policies and are computed using the net level premium method, which incorporates actuarial assumptions as to morbidity, persistency, inclusive of mortality, discount rate, future premium rate adjustments and expenses. Expense assumptions primarily relate to claim adjudication. The Company's future policy benefit reserves are based on best estimate actuarial assumptions as of the most recent date of loss recognition, which occurred in 2015. If a premium deficiency were to emerge in the future, the assumptions would be unlocked, and the future policy benefit reserves would be adjusted. The GPV process was performed in the third quarter of 2018 as compared to the fourth quarter in 2017. The GPV as of September 30, 2018 and December 31, 2017 indicated the carried reserves were sufficient; therefore, there was no unlocking of assumptions. Interest rates for long term care active life reserves range from 6.6% to 7.0% as of September 30, 2018 and December 31, 2017 . The Company's most recent GPV indicated the future policy benefit reserves for the long term care business were not deficient in the aggregate, but profits are expected to be recognized in early years followed by losses in later years. In that circumstance, future policy benefit reserves are increased in the profitable years by an amount necessary to offset losses that are projected to be recognized in later years. The amount of the additional future policy benefit reserves recorded in each quarterly period is determined by applying the ratio of the present value of future losses divided by the present value of future profits from the most recently completed GPV to long term care core income in that period. Guaranty fund and other insurance-related assessments: Liabilities for guaranty fund and other insurance-related assessments are accrued when an assessment is probable, when it can be reasonably estimated and when the event obligating the entity to pay an imposed or probable assessment has occurred. Liabilities for guaranty funds and other insurance-related assessments are not discounted and are included as part of Other liabilities on the Consolidated Balance Sheets. As of December 31, 2018 and 2017 , the liability balances were $108 million and $121 million . Reinsurance: Reinsurance accounting allows for contractual cash flows to be reflected as premiums and losses. To qualify for reinsurance accounting, reinsurance agreements must include risk transfer. To meet risk transfer requirements, a reinsurance contract must include both insurance risk, consisting of underwriting and timing risk, and a reasonable possibility of a significant loss for the assuming entity. Reinsurance receivables related to paid losses are presented at unpaid balances. Reinsurance receivables related to unpaid losses are estimated in a manner consistent with claim and claim adjustment expense reserves or future policy benefit reserves. Reinsurance receivables are reported net of an allowance for uncollectible amounts on the Consolidated Balance Sheets. The cost of reinsurance is primarily accounted for over the life of the underlying reinsured policies using assumptions consistent with those used to account for the underlying policies or over the reinsurance contract period. The ceding of insurance does not discharge the primary liability of the Company. The Company has established an allowance for uncollectible reinsurance receivables which relates to both amounts already billed on ceded paid losses as well as ceded reserves that will be billed when losses are paid in the future. The allowance for uncollectible reinsurance receivables is estimated on the basis of periodic evaluations of balances due from reinsurers, reinsurer solvency, industry experience and current economic conditions. Reinsurer financial strength ratings are updated and reviewed on an annual basis or sooner if the Company becomes aware of significant changes related to a reinsurer. Because billed receivables generally approximate 5% or less of total reinsurance receivables, the age of the reinsurance receivables related to paid losses is not a significant input into the allowance analysis. Changes in the allowance for uncollectible reinsurance receivables are presented as a component of Insurance claims and policyholders' benefits on the Consolidated Statements of Operations. Amounts are considered past due based on the reinsurance contract terms. Reinsurance receivables related to paid losses and any related allowance are written off after collection efforts have been exhausted or a negotiated settlement is reached with the reinsurer. Reinsurance receivables from insolvent insurers related to paid losses are written off when the settlement due from the estate can be reasonably estimated. At the time reinsurance receivables related to paid losses are written off, any required adjustment to reinsurance receivables related to unpaid losses is recorded as a component of Insurance claims and policyholders' benefits on the Consolidated Statements of Operations. Reinsurance contracts that do not effectively transfer the economic risk of loss on the underlying policies are recorded using the deposit method of accounting, which requires that premium paid or received by the ceding company or assuming company be accounted for as a deposit asset or liability. The Company had $3 million and $8 million recorded as deposit assets as of December 31, 2018 and 2017 , and $3 million and $4 million recorded as deposit liabilities as of December 31, 2018 and 2017 . Income on reinsurance contracts accounted for under the deposit method is recognized using an effective yield based on the anticipated timing of payments and the remaining life of the contract. When the anticipated timing of payments changes, the effective yield is recalculated to reflect actual payments to date and the estimated timing of future payments. The deposit asset or liability is adjusted to the amount that would have existed had the new effective yield been applied since the inception of the contract. A loss portfolio transfer is a retroactive reinsurance contract. If the cumulative claim and allocated claim adjustment expenses ceded under a loss portfolio transfer exceed the consideration paid, the resulting gain from such excess is deferred and amortized into earnings in future periods in proportion to actual recoveries under the loss portfolio transfer. In any period in which there is a revised estimate of claim and allocated claim adjustment expenses and the loss portfolio transfer is in a gain position, the deferred gain is recalculated as if the revised estimate was available at the inception date of the loss portfolio transfer and the change in the deferred gain is recognized in earnings. Deferred acquisition costs: Deferrable acquisition costs include commissions, premium taxes and certain underwriting and policy issuance costs which are incremental direct costs of successful contract acquisitions. Acquisition costs related to property and casualty business are deferred and amortized ratably over the period the related premiums are earned. Deferred acquisition costs are presented net of ceding commissions and other ceded acquisition costs. The Company evaluates deferred acquisition costs for recoverability. Anticipated investment income is considered in the determination of the recoverability of deferred acquisition costs. Adjustments, if necessary, are recorded in current period results of operations. Investments in life settlement contracts and related revenue recognition: The Company formerly held investments in life settlement contracts. The entire portfolio of life settlement contracts was determined to be held for sale as of December 31, 2016. The Company reached an agreement on terms to sell the portfolio and adjusted the fair value to the estimated sales proceeds less cost to sell. This resulted in a $10 million loss recognized within Net realized investment gains for the year ended December 31, 2016. The sale was completed during 2017 and the Company recorded the consideration, including a note receivable, which is payable over three years and is carried at amortized cost less any valuation allowance. The note receivable was $35 million and $46 million as of December 31, 2018 and 2017 and is included within Other assets on the Consolidated Balance Sheets. Interest income is accreted to the principal balance of the note. The cash receipts and payments related to the life settlement contracts prior to the sale date are included in Cash Flows from operating activities on the Consolidated Statements of Cash Flows. Cash receipts related to the sale of the life settlement contracts, as well as principal payments on the note receivable, are included in Cash Flows from investing activities. Investments The Company classifies its fixed maturity securities as either available-for-sale or trading, and as such, they are carried at fair value. Changes in fair value of trading securities are reported within Net investment income on the Consolidated Statements of Operations. Changes in fair value related to available-for-sale securities are reported as a component of Other comprehensive income. Losses may be recognized within Net realized investment gains (losses) on the Consolidated Statements of Operations when a decline in value is determined by the Company to be other-than-temporary. The cost of fixed maturity securities classified as available-for-sale is adjusted for amortization of premiums and accretion of discounts, which are included in Net investment income on the Consolidated Statements of Operations. The amortization of premium and accretion of discount for fixed maturity securities takes into consideration call and maturity dates that produce the lowest yield. For asset-backed securities included in fixed maturity securities, the Company recognizes income using an effective yield based on anticipated prepayments and the estimated economic life of the securities. When estimates of prepayments change, the effective yield is recalculated to reflect actual payments to date and anticipated future payments. To the extent that unrealized gains on fixed maturity securities supporting long term care products and structured settlements not funded by annuities would result in a premium deficiency if those gains were realized, a related increase in Insurance reserves is recorded, net of tax, as a reduction of net unrealized gains through Other comprehensive income (Shadow Adjustments). Shadow Adjustments, net of tax, decreased $333 million and increased $397 million for the years ended December 31, 2018 and 2017 , respectively. As of December 31, 2018 and 2017 , net unrealized gains on investments included in Accumulated other comprehensive income (AOCI) were correspondingly reduced by Shadow Adjustments of $1,078 million and $1,411 million . Equity securities are carried at fair value. The Company's non-redeemable preferred stock contain characteristics of debt securities, are priced similarly to bonds and are held primarily for income generation through periodic dividends. While recognition of gains and losses on these securities is not discretionary, management does not consider the changes in fair value of non-redeemable preferred stock to be reflective of our primary operations. As such, the changes in the fair value of these securities are recorded through Net realized investments gains (losses). The Company owns certain common stock with the intention of holding the securities primarily for market ap

Investments

Investments	12 Months Ended
	Dec. 31, 2018
Investments [Abstract]
Investments	Investments The significant components of Net investment income are presented in the following table. Years ended December 31 (In millions) 2018 2017 2016 Fixed maturity securities $ 1,795 $ 1,812 $ 1,819 Equity securities 18 12 10 Limited partnership investments (22 ) 207 155 Mortgage loans 50 34 41 Short term investments 26 15 8 Trading portfolio 7 12 10 Other 4 1 4 Gross investment income 1,878 2,093 2,047 Investment expense (61 ) (59 ) (59 ) Net investment income $ 1,817 $ 2,034 $ 1,988 For the year ended December 31, 2018 , Net investment income was reduced by $24 million due to the change in fair value of common stock still held as of December 31, 2018 . As of December 31, 2018 the Company held no non-income producing fixed maturity securities. As of December 31, 2017 the Company held $2 million of non-income producing fixed maturity securities. As of December 31, 2018 and 2017 , no investments in a single issuer exceeded 10% of stockholders' equity, other than investments in securities issued by the U.S. Treasury and obligations of government-sponsored enterprises. Net realized investment gains (losses) are presented in the following table. Years ended December 31 (In millions) 2018 2017 2016 Net realized investment gains (losses): Fixed maturity securities: Gross realized gains $ 168 $ 186 $ 204 Gross realized losses (164 ) (64 ) (138 ) Net realized investment gains (losses) on fixed maturity securities 4 122 66 Equity securities (74 ) — (5 ) Derivatives 9 (4 ) (2 ) Short term investments and other 9 (25 ) (9 ) Net realized investment gains (losses) $ (52 ) $ 93 $ 50 For the year ended December 31, 2018 , Net realized investment gains (losses) were reduced by $73 million due to the change in fair value of non-redeemable preferred stock still held as of December 31, 2018 . Net realized investment gains (losses) for the year ended December 31, 2017 included a $42 million loss related to the redemption of the Company's $350 million senior notes due November 2019. Net change in unrealized gains on investments is presented in the following table. Years ended December 31 (In millions) 2018 2017 2016 Net change in unrealized gains on investments: Fixed maturity securities $ (1,811 ) $ 728 $ 225 Equity securities (1) — 32 (2 ) Other — (2 ) 1 Total net change in unrealized gains on investments $ (1,811 ) $ 758 $ 224 (1) As of January 1, 2018, the Company adopted ASU 2016-01, Financial Instruments - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities . The change in fair value of equity securities is now recognized through the income statement. See Note A to the Consolidated Financial Statements for additional information. The components of OTTI losses recognized in earnings by asset type are presented in the following table. Years ended December 31 (In millions) 2018 2017 2016 Fixed maturity securities available-for-sale: Corporate and other bonds $ 12 $ 12 $ 59 Asset-backed 9 1 13 Total fixed maturity securities available-for-sale 21 13 72 Equity securities available-for-sale — 1 9 OTTI losses recognized in earnings $ 21 $ 14 $ 81 The following tables present a summary of fixed maturity and equity securities. December 31, 2018 (1) Cost or Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Unrealized OTTI Losses (Gains) (In millions) Fixed maturity securities available-for-sale: Corporate and other bonds $ 18,764 $ 791 $ 395 $ 19,160 $ — States, municipalities and political subdivisions 9,681 1,076 9 10,748 — Asset-backed: Residential mortgage-backed 4,815 68 57 4,826 (20 ) Commercial mortgage-backed 2,200 28 32 2,196 — Other asset-backed 1,975 11 24 1,962 — Total asset-backed 8,990 107 113 8,984 (20 ) U.S. Treasury and obligations of government-sponsored enterprises 156 3 — 159 — Foreign government 480 5 4 481 — Redeemable preferred stock 10 — — 10 — Total fixed maturity securities available-for-sale 38,081 1,982 521 39,542 $ (20 ) Total fixed maturity securities trading 4 — — 4 Total fixed maturity securities $ 38,085 $ 1,982 $ 521 $ 39,546 December 31, 2017 Cost or Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Unrealized OTTI Losses (Gains) (In millions) Fixed maturity securities available-for-sale: Corporate and other bonds $ 17,210 $ 1,625 $ 28 $ 18,807 $ — States, municipalities and political subdivisions 12,478 1,551 2 14,027 (11 ) Asset-backed: Residential mortgage-backed 5,043 109 32 5,120 (27 ) Commercial mortgage-backed 1,840 46 14 1,872 — Other asset-backed 1,083 16 5 1,094 — Total asset-backed 7,966 171 51 8,086 (27 ) U.S. Treasury and obligations of government-sponsored enterprises 111 2 4 109 — Foreign government 437 9 2 444 — Redeemable preferred stock 10 1 — 11 — Total fixed maturity securities available-for-sale 38,212 3,359 87 41,484 $ (38 ) Total fixed maturity securities trading 3 — — 3 Equity securities available-for-sale: Common stock 21 7 1 27 Preferred stock 638 31 1 668 Total equity securities available-for-sale 659 38 2 695 Total fixed maturity and equity securities $ 38,874 $ 3,397 $ 89 $ 42,182 (1) As of January 1, 2018, the Company adopted ASU 2016-01, Financial Instruments - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities . The change in fair value of equity securities is now recognized through the income statement. See Note A to the Consolidated Financial Statements for additional information. The following tables present the estimated fair value and gross unrealized losses of fixed maturity and equity securities in a gross unrealized loss position by the length of time in which the securities have continuously been in that position. Less than 12 Months 12 Months or Longer Total December 31, 2018 (1) Estimated Fair Value Gross Unrealized Losses Estimated Fair Value Gross Unrealized Losses Estimated Fair Value Gross Unrealized Losses (In millions) Fixed maturity securities available-for-sale: Corporate and other bonds $ 8,543 $ 340 $ 825 $ 55 $ 9,368 $ 395 States, municipalities and political subdivisions 517 8 5 1 522 9 Asset-backed: Residential mortgage-backed 1,932 23 1,119 34 3,051 57 Commercial mortgage-backed 728 10 397 22 1,125 32 Other asset-backed 834 21 125 3 959 24 Total asset-backed 3,494 54 1,641 59 5,135 113 U.S. Treasury and obligations of government-sponsored enterprises 21 — 19 — 40 — Foreign government 114 2 124 2 238 4 Total $ 12,689 $ 404 $ 2,614 $ 117 $ 15,303 $ 521 Less than 12 Months 12 Months or Longer Total December 31, 2017 Estimated Fair Value Gross Unrealized Losses Estimated Fair Value Gross Unrealized Losses Estimated Fair Value Gross Unrealized Losses (In millions) Fixed maturity securities available-for-sale: Corporate and other bonds $ 1,354 $ 21 $ 168 $ 7 $ 1,522 $ 28 States, municipalities and political subdivisions 72 1 85 1 157 2 Asset-backed: Residential mortgage-backed 1,228 5 947 27 2,175 32 Commercial mortgage-backed 403 4 212 10 615 14 Other asset-backed 248 3 18 2 266 5 Total asset-backed 1,879 12 1,177 39 3,056 51 U.S. Treasury and obligations of government-sponsored enterprises 49 2 21 2 70 4 Foreign government 166 2 4 — 170 2 Total fixed maturity securities available-for-sale 3,520 38 1,455 49 4,975 87 Equity securities available-for-sale: Common stock 7 1 — — 7 1 Preferred stock 93 1 — — 93 1 Total equity securities available-for-sale 100 2 — — 100 2 Total $ 3,620 $ 40 $ 1,455 $ 49 $ 5,075 $ 89 (1) As of January 1, 2018, the Company adopted ASU 2016-01, Financial Instruments - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities . The change in fair value of equity securities is now recognized through the income statement. See Note A to the Consolidated Financial Statements for additional information. Based on current facts and circumstances, the Company believes the unrealized losses presented in the December 31, 2018 securities in a gross unrealized loss position table above are not indicative of the ultimate collectibility of the current amortized cost of the securities, but rather are attributable to changes in interest rates, credit spreads and other factors. The Company has no current intent to sell securities with unrealized losses, nor is it more likely than not that it will be required to sell prior to recovery of amortized cost; accordingly, the Company has determined that there are no additional OTTI losses to be recorded as of December 31, 2018 . The following table presents the activity related to the pretax credit loss component reflected in Retained earnings on fixed maturity securities still held as of December 31, 2018 , 2017 and 2016 for which a portion of an OTTI loss was recognized in Other comprehensive income (loss). Years ended December 31 (In millions) 2018 2017 2016 Beginning balance of credit losses on fixed maturity securities $ 27 $ 36 $ 53 Reductions for securities sold during the period (9 ) (9 ) (16 ) Reductions for securities the Company intends to sell or more likely than not will be required to sell — — (1 ) Ending balance of credit losses on fixed maturity securities $ 18 $ 27 $ 36 Contractual Maturity The following table presents available-for-sale fixed maturity securities by contractual maturity. December 31 2018 2017 (In millions) Cost or Amortized Cost Estimated Fair Value Cost or Amortized Cost Estimated Fair Value Due in one year or less $ 1,350 $ 1,359 $ 1,135 $ 1,157 Due after one year through five years 7,979 8,139 8,165 8,501 Due after five years through ten years 16,859 16,870 16,060 16,718 Due after ten years 11,893 13,174 12,852 15,108 Total $ 38,081 $ 39,542 $ 38,212 $ 41,484 Actual maturities may differ from contractual maturities because certain securities may be called or prepaid. Securities not due at a single date are allocated based on weighted average life. Limited Partnerships The carrying value of limited partnerships as of December 31, 2018 and 2017 was $1,982 million and $2,369 million , which includes net undistributed earnings of $153 million and $539 million . Limited partnerships comprising 60% of the total carrying value are reported on a current basis through December 31, 2018 with no reporting lag, 14% are reported on a one month lag and the remainder are reported on more than a one month lag. The number of limited partnerships held and the strategies employed provide diversification to the limited partnership portfolio and the overall invested asset portfolio. Limited partnerships comprising 65% and 71% of the carrying value as of December 31, 2018 and 2017 employ hedge fund strategies. Limited partnerships comprising 30% and 25% of the carrying value as of December 31, 2018 and 2017 were invested in private debt and equity. The remainder was primarily invested in real estate strategies. Hedge fund strategies include both long and short positions in fixed income, equity and derivative instruments. These hedge fund strategies may seek to generate gains from mispriced or undervalued securities, price differentials between securities, distressed investments, sector rotation or various arbitrage disciplines. Within hedge fund strategies, approximately 60% were equity related, 18% pursued a multi-strategy approach, 19% were focused on distressed investments and 3% were fixed income related as of December 31, 2018 . The ten largest limited partnership positions held totaled $876 million and $1,136 million as of December 31, 2018 and 2017 . Based on the most recent information available regarding the Company’s percentage ownership of the individual limited partnerships, the carrying value reflected on the Consolidated Balance Sheets represents approximately 2% and 3% of the aggregate partnership equity as of December 31, 2018 and 2017 , and the related income reflected on the Consolidated Statements of Operations represents approximately 3% , 3% and 4% of the changes in aggregate partnership equity for the years ended December 31, 2018 , 2017 and 2016 . While the Company generally does not invest in highly leveraged partnerships, there are risks inherent in limited partnership investments which may result in losses due to short-selling, derivatives or other speculative investment practices. The use of leverage increases volatility generated by the underlying investment strategies. The Company’s limited partnership investments contain withdrawal provisions that generally limit liquidity for a period of thirty days up to one year and in some cases do not permit withdrawals until the termination of the partnership. Typically, withdrawals require advance written notice of up to 90 days. Derivative Financial Instruments The Company may use derivatives in the normal course of business, primarily in an attempt to reduce its exposure to market risk (principally interest rate risk, credit risk, equity price risk and foreign currency risk) stemming from various assets and liabilities. The Company's principal objective under such strategies is to achieve the desired reduction in economic risk, even if the position does not receive hedge accounting treatment. The Company may enter into interest rate swaps, futures and forward commitments to purchase securities to manage interest rate risk. The Company may use foreign currency forward contracts to manage foreign currency risk. Credit exposure associated with non-performance by the counterparties to derivative instruments is generally limited to the uncollateralized fair value of the asset related to the instruments recognized on the Consolidated Balance Sheets. The Company generally requires that all over-the-counter derivative contracts be governed by an International Swaps and Derivatives Association Master Agreement, and exchanges collateral under the terms of these agreements with its derivative investment counterparties depending on the amount of the exposure and the credit rating of the counterparty. Gross estimated fair values of derivative positions are presented in Other invested assets and Other liabilities on the Consolidated Balance Sheets. The Company does not offset derivative positions against the fair value of collateral provided or positions subject to netting arrangements. There would be no significant difference in the balance included in such accounts if the estimated fair values were presented net as of December 31, 2018 and 2017 . There was no cash collateral provided by the Company as of December 31, 2018 or 2017 . There was no cash collateral received from counterparties held as of December 31, 2018 or 2017 . The Company holds an embedded derivative on a funds withheld liability with a notional value of $172 million and $167 million as of December 31, 2018 and 2017 and a fair value of $4 million and $(3) million as of December 31, 2018 and 2017 . The embedded derivative on the funds withheld liability is accounted for separately and reported with the funds withheld liability in Other liabilities on the Consolidated Balance Sheets. Investment Commitments As of December 31, 2018 , the Company had committed approximately $574 million to future capital calls from various third-party limited partnership investments in exchange for an ownership interest in the related partnerships. As of December 31, 2018 , the Company had mortgage loan commitments of $59 million representing signed loan applications received and accepted. The Company invests in various privately placed debt securities, including bank loans, as part of its overall investment strategy and has committed to additional future purchases, sales and funding. Purchases and sales of privately placed debt securities are recorded once funded. As of December 31, 2018 , the Company had commitments to purchase or fund additional amounts of $230 million and sell $78 million under the terms of such securities. Investments on Deposit Securities with carrying values of approximately $2.5 billion and $2.6 billion were deposited by the Company’s insurance subsidiaries under requirements of regulatory authorities and others as of December 31, 2018 and 2017 . Cash and securities with carrying values of approximately $1.0 billion and $1.1 billion were deposited with financial institutions in trust accounts or as collateral for letters of credit to secure obligations with various third parties as of December 31, 2018 and 2017 .

Fair Value

Fair Value	12 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Fair Value	Fair Value Fair value is the price that would be received upon sale of an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. The following fair value hierarchy is used in selecting inputs, with the highest priority given to Level 1, as these are the most transparent or reliable. Level 1 - Quoted prices for identical instruments in active markets. Level 2 - Quoted prices for similar instruments in active markets; quoted prices for identical or similar instruments in markets that are not active; and model-derived valuations in which all significant inputs are observable in active markets. Level 3 - Valuations derived from valuation techniques in which one or more significant inputs are not observable. Prices may fall within Level 1, 2 or 3 depending upon the methodology and inputs used to estimate fair value for each specific security. In general, the Company seeks to price securities using third-party pricing services. Securities not priced by pricing services are submitted to independent brokers for valuation and, if those are not available, internally developed pricing models are used to value assets using a methodology and inputs the Company believes market participants would use to value the assets. Prices obtained from third-party pricing services or brokers are not adjusted by the Company. The Company performs control procedures over information obtained from pricing services and brokers to ensure prices received represent a reasonable estimate of fair value and to confirm representations regarding whether inputs are observable or unobservable. Procedures may include i) the review of pricing service methodologies or broker pricing qualifications, ii) back-testing, where past fair value estimates are compared to actual transactions executed in the market on similar dates, iii) exception reporting, where period-over-period changes in price are reviewed and challenged with the pricing service or broker based on exception criteria, iv) deep dives, where the Company performs an independent analysis of the inputs and assumptions used to price individual securities and v) pricing validation, where prices received are compared to prices independently estimated by the Company. Assets and Liabilities Measured at Fair Value Assets and liabilities measured at fair value on a recurring basis are presented in the following tables. Corporate bonds and other includes obligations of the U.S. Treasury, government-sponsored enterprises, foreign governments and redeemable preferred stock. December 31, 2018 Total Assets/Liabilities at Fair Value (In millions) Level 1 Level 2 Level 3 Assets Fixed maturity securities: Corporate bonds and other $ 196 $ 19,396 $ 222 $ 19,814 States, municipalities and political subdivisions — 10,748 — 10,748 Asset-backed — 8,787 197 8,984 Total fixed maturity securities 196 38,931 419 39,546 Equity securities: Common stock 144 — 4 148 Non-redeemable preferred stock 48 570 14 632 Total equity securities 192 570 18 780 Short term and other 216 949 — 1,165 Total assets $ 604 $ 40,450 $ 437 $ 41,491 Liabilities Other liabilities $ — $ (4 ) $ — $ (4 ) Total liabilities $ — $ (4 ) $ — $ (4 ) December 31, 2017 Total Assets/Liabilities at Fair Value (In millions) Level 1 Level 2 Level 3 Assets Fixed maturity securities: Corporate bonds and other $ 128 $ 19,148 $ 98 $ 19,374 States, municipalities and political subdivisions — 14,026 1 14,027 Asset-backed — 7,751 335 8,086 Total fixed maturity securities 128 40,925 434 41,487 Equity securities: Common stock 23 — 4 27 Non-redeemable preferred stock 68 584 16 668 Total equity securities 91 584 20 695 Short term and other 396 958 — 1,354 Total assets $ 615 $ 42,467 $ 454 $ 43,536 Liabilities Other liabilities $ — $ 3 $ — $ 3 Total liabilities $ — $ 3 $ — $ 3 The tables below present a reconciliation for all assets and liabilities measured at fair value on a recurring basis using significant unobservable inputs (Level 3). Level 3 (In millions) Corporate bonds and other States, municipalities and political subdivisions Asset-backed Equity securities Derivative financial instruments Total Balance as of January 1, 2018 $ 98 $ 1 $ 335 $ 20 $ — $ 454 Total realized and unrealized investment gains (losses): Reported in Net realized investment gains (losses) (1 ) — 5 (2 ) — 2 Reported in Net investment income — — — — — — Reported in Other comprehensive income (loss) (4 ) — (8 ) — — (12 ) Total realized and unrealized investment gains (losses) (5 ) — (3 ) (2 ) — (10 ) Purchases 117 — 162 — — 279 Sales (5 ) — (72 ) — — (77 ) Settlements (9 ) (1 ) (64 ) — — (74 ) Transfers into Level 3 35 — 42 — — 77 Transfers out of Level 3 (9 ) — (203 ) — — (212 ) Balance as of December 31, 2018 $ 222 $ — $ 197 $ 18 $ — $ 437 Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2018 recognized in Net income (loss) $ — $ — $ (2 ) $ (2 ) $ — $ (4 ) Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2018 recognized in Other comprehensive income (loss) (5 ) — (4 ) — — (9 ) Level 3 (In millions) Corporate bonds and other States, municipalities and political subdivisions Asset-backed Equity securities Derivative financial instruments Life settlement contracts Total Balance as of January 1, 2017 $ 130 $ 1 $ 199 $ 19 $ — $ 58 $ 407 Total realized and unrealized investment gains (losses): Reported in Net realized investment gains (losses) — — 2 — 1 — 3 Reported in Other revenues — — — — — 6 6 Reported in Other comprehensive income (loss) 3 — 3 3 — — 9 Total realized and unrealized investment gains (losses) 3 — 5 3 1 6 18 Purchases 18 — 107 1 — — 126 Sales (5 ) — — (3 ) (1 ) (59 ) (68 ) Settlements (54 ) — (43 ) — — (5 ) (102 ) Transfers into Level 3 16 — 153 — — — 169 Transfers out of Level 3 (10 ) — (86 ) — — — (96 ) Balance as of December 31, 2017 $ 98 $ 1 $ 335 $ 20 $ — $ — $ 454 Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2017 recognized in Net income (loss) $ — $ — $ — $ — $ — $ — $ — Securities may be transferred in or out of levels within the fair value hierarchy based on the availability of observable market information and quoted prices used to determine the fair value of the security. The availability of observable market information and quoted prices varies based on market conditions and trading volume. Valuation Methodologies and Inputs The following section describes the valuation methodologies and relevant inputs used to measure different financial instruments at fair value, including an indication of the level in the fair value hierarchy in which the instruments are generally classified. Fixed Maturity Securities Level 1 securities include highly liquid and exchange traded bonds and redeemable preferred stock, valued using quoted market prices. Level 2 securities include most other fixed maturity securities as the significant inputs are observable in the marketplace. All classes of Level 2 fixed maturity securities are valued using a methodology based on information generated by market transactions involving identical or comparable assets, a discounted cash flow methodology, or a combination of both when necessary. Common inputs for all classes of fixed maturity securities include prices from recently executed transactions of similar securities, marketplace quotes, benchmark yields, spreads off benchmark yields, interest rates and U.S. Treasury or swap curves. Specifically for asset-backed securities, key inputs include prepayment and default projections based on past performance of the underlying collateral and current market data. Fixed maturity securities are primarily assigned to Level 3 in cases where broker/dealer quotes are significant inputs to the valuation and there is a lack of transparency as to whether these quotes are based on information that is observable in the marketplace. Level 3 securities also include private placement debt securities whose fair value is determined using internal models with inputs that are not market observable. Equity Securities Level 1 equity securities include publicly traded securities valued using quoted market prices. Level 2 securities are primarily valued using pricing for similar securities, recently executed transactions and other pricing models utilizing market observable inputs. Level 3 securities are primarily priced using broker/dealer quotes and internal models with inputs that are not market observable. Short Term and Other Invested Assets Securities that are actively traded or have quoted prices are classified as Level 1. These securities include money market funds and treasury bills. Level 2 primarily includes commercial paper, for which all inputs are market observable. Fixed maturity securities purchased within one year of maturity are classified consistent with fixed maturity securities discussed above. Short term investments as presented in the tables above differ from the amounts presented on the Consolidated Balance Sheets because certain short term investments, such as time deposits, are not measured at fair value. As of December 31, 2018 and December 31, 2017 , there were approximately $ 48 million and $39 million of overseas deposits within other invested assets, which can be redeemed at net asset value in 90 days or less. Overseas deposits are excluded from the fair value hierarchy because their fair value is recorded using the net asset value per share (or equivalent) practical expedient. Life Settlement Contracts The Company sold its life settlement contracts to a third party in 2017. The valuation of the life settlement contracts was based on the terms of sale. The contracts were classified as Level 3 as there was not an active market for life settlement contracts. Derivative Financial Investments Level 2 investments primarily include the embedded derivative on the funds withheld liability. The embedded derivative on funds withheld liability is valued using the change in fair value of the assets supporting the funds withheld liability, which are fixed maturity securities valued with observable inputs. Significant Unobservable Inputs The following tables present quantitative information about the significant unobservable inputs utilized by the Company in the fair value measurements of Level 3 assets. Valuations for assets and liabilities not presented in the tables below are primarily based on broker/dealer quotes for which there is a lack of transparency as to inputs used to develop the valuations. The quantitative detail of these unobservable inputs is neither provided nor reasonably available to the Company. The weighted average rate is calculated based on fair value. December 31, 2018 Estimated Fair Value (In millions) Valuation Technique(s) Unobservable Input(s) Range (Weighted Average) Fixed maturity securities $ 228 Discounted cash flow Credit spread 1% - 12% (3%) December 31, 2017 Estimated Fair Value Valuation Technique(s) Unobservable Input(s) Range (Weighted Average) Fixed maturity securities $ 136 Discounted cash flow Credit spread 1% - 12% (3%) For fixed maturity securities, an increase to the credit spread assumptions would result in a lower fair value measurement. Financial Assets and Liabilities Not Measured at Fair Value The carrying amount and estimated fair value of the Company's financial assets and liabilities which are not measured at fair value on the Consolidated Balance Sheets are presented in the following tables. December 31, 2018 Carrying Amount Estimated Fair Value (In millions) Level 1 Level 2 Level 3 Total Assets Mortgage loans $ 839 $ — $ — $ 827 $ 827 Note receivable 35 — — 35 35 Liabilities Long term debt $ 2,680 $ — $ 2,731 $ — $ 2,731 December 31, 2017 Carrying Estimated Fair Value (In millions) Level 1 Level 2 Level 3 Total Assets Mortgage loans $ 839 $ — $ — $ 844 $ 844 Note receivable 46 — — 46 46 Liabilities Short term debt $ 150 $ — $ 150 $ — $ 150 Long term debt 2,708 — 2,896 — 2,896 The following methods and assumptions were used to estimate the fair value of these financial assets and liabilities. The fair values of mortgage loans were based on the present value of the expected future cash flows discounted at the current interest rate for origination of similar quality loans, adjusted for specific loan risk. The fair value of the note receivable was based on the present value of the expected future cash flows discounted at the current interest rate for origination of similar notes, adjusted for specific credit risk. The note receivable is included within Other assets on the Consolidated Balance Sheets. The Company's senior notes and debentures were valued based on observable market prices. The fair value for other debt was estimated using discounted cash flows based on current incremental borrowing rates for similar borrowing arrangements. The carrying amounts reported on the Consolidated Balance Sheets for Cash, Short term investments not carried at fair value, Accrued investment income and certain Other assets and Other liabilities approximate fair value due to the short term nature of these items. These assets and liabilities are not listed in the tables above.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The CNA Tax Group is included in the consolidated federal income tax return of Loews and its eligible subsidiaries. Loews and the Company have agreed that for each taxable year, the Company will 1) be paid by Loews the amount, if any, by which the Loews consolidated federal income tax liability is reduced by virtue of the inclusion of the CNA Tax Group in the Loews consolidated federal income tax return, or 2) pay to Loews an amount, if any, equal to the federal income tax that would have been payable by the CNA Tax Group filing a separate consolidated tax return. In the event that Loews should have a net operating loss in the future computed on the basis of filing a separate consolidated tax return without the CNA Tax Group, the Company may be required to repay tax recoveries previously received from Loews. This agreement may be canceled by either party upon 30 days written notice. For the years ended December 31, 2018 , 2017 and 2016 , the Company paid $275 million , $127 million and $142 million to Loews related to federal income taxes. For 2016 through 2018 , the Internal Revenue Service (IRS) has accepted Loews and the Company into the Compliance Assurance Process (CAP), which is a voluntary program for large corporations. Under CAP, the IRS conducts a real-time audit and works contemporaneously with the Company to resolve any issues prior to the filing of the tax return. The Company believes that this approach should reduce tax-related uncertainties, if any. As of December 31, 2018 and 2017 , there were no unrecognized tax benefits. The Company recognizes interest accrued related to: 1) unrecognized tax benefits in Interest expense and 2) tax refund claims in Other revenues on the Consolidated Statements of Operations. The Company recognizes penalties (if any) in Income tax (expense) benefit on the Consolidated Statements of Operations. During 2018 , 2017 and 2016 the Company recognized no interest and no penalties. There were no amounts accrued for interest or penalties as of December 31, 2018 or 2017 . On December 22, 2017, H.R.1, “An Act to Provide for Reconciliation Pursuant to Titles II and V of the Concurrent Resolution on the Budget for Fiscal Year 2018,” was signed into law (Tax Reform Legislation). Shortly after enactment, the Securities and Exchange Commission Staff issued Staff Accounting Bulletin No. 118 (SAB 118) to provide guidance on accounting for the Tax Reform Legislation impacts when the measurements of the income tax effects are complete, incomplete, or incomplete but for which a provisional amount can be estimated. SAB 118 permitted the recognition of provisional amounts, and adjustments to provisional amounts, in subsequent reporting periods within a one year measurement period. At December 31, 2017, the Company had significant provisional items as set forth below. • The Company re-computed its insurance reserves and the transition adjustment from existing law. • The Company computed amounts under special accounting method provisions for recognizing income for Federal income tax purposes no later than for financial accounting purposes and the transition adjustment from existing law. • The Company did not record current or deferred taxes with respect to the international provisions since it did not expect to have inclusions in U.S. taxable income for certain earnings of foreign subsidiaries in future years. Adjustments to the Company's provisional amounts for the year ended December 31, 2018 did not impact the effective tax rate. The Tax Reform Legislation provided for a permanent reduction in the Federal corporate income tax rate from 35% to 21% effective January 1, 2018, among other provisions. The Company was required to recognize the effect of the tax rate change on its deferred tax assets in the period the tax rate change was signed into law. Consequently, the Company recorded a non-cash increase to Income tax expense of $83 million in the Consolidated Statements of Operations for the year ended December 31, 2017 . Based on the filed 2017 tax return, the effect of the tax rate change decreased Income tax expense by $6 million for the year ended December 31, 2018 . At December 31, 2018, measurement of the income tax effects of the Tax Reform Legislation is complete. The following table presents a reconciliation between the Company's federal income tax expense at statutory rates and the recorded income tax expense. Years ended December 31 (In millions) 2018 2017 2016 Income tax expense at statutory rates $ (203 ) $ (459 ) $ (398 ) Tax benefit from tax exempt income 63 131 124 Foreign taxes and credits (1 ) 3 3 State income taxes (13 ) (7 ) (6 ) Net deferred tax asset remeasurement 6 (83 ) — Other tax expense (3 ) 4 (1 ) Income tax expense $ (151 ) $ (411 ) $ (278 ) As of December 31, 2018 , no deferred taxes are required on the undistributed earnings of subsidiaries subject to tax. The following table presents the current and deferred components of the Company's income tax expense. Years ended December 31 (In millions) 2018 2017 2016 Current tax expense $ (171 ) $ (243 ) $ (142 ) Deferred tax benefit (expense) 20 (168 ) (136 ) Total income tax expense $ (151 ) $ (411 ) $ (278 ) Total income tax presented above includes foreign tax (expense)/benefit of approximately $(5) million , $1 million and $(9) million related to pretax income from foreign operations of approximately $22 million , $39 million and $51 million for the years ended December 31, 2018 , 2017 and 2016 . The deferred tax effects of the significant components of the Company's deferred tax assets and liabilities are presented in the following table. December 31 (In millions) 2018 2017 Deferred Tax Assets: Insurance reserves: Property and casualty claim and claim adjustment expense reserves $ 108 $ 74 Unearned premium reserves 108 142 Receivables 15 15 Employee benefits 143 154 Deferred retroactive reinsurance benefit 79 68 Other assets 131 105 Gross deferred tax assets 584 558 Deferred Tax Liabilities: Investment valuation differences 44 55 Deferred acquisition costs 78 77 Net unrealized gains 14 233 Software and hardware 44 46 Other liabilities 12 10 Gross deferred tax liabilities 192 421 Net deferred tax asset $ 392 $ 137 As of December 31, 2018 , the CNA Tax Group had no loss carryforwards or tax credit carryforwards. Although realization of deferred tax assets is not assured, management believes it is more likely than not that the recognized net deferred tax asset will be realized through recoupment of ordinary and capital taxes paid in prior carryback years and through future earnings, reversal of existing temporary differences and available tax planning strategies. As a result, no valuation allowance was recorded as of December 31, 2018 or 2017 .

Claim and Claim Adjustment Expe

Claim and Claim Adjustment Expense Reserves	12 Months Ended
	Dec. 31, 2018
Liability for Claims and Claims Adjustment Expense [Abstract]
Claim and Claim Adjustment Expense Reserves	Claim and Claim Adjustment Expense Reserves Property and casualty insurance claim and claim adjustment expense reserves represent the estimated amounts necessary to resolve all outstanding claims, including IBNR claims as of the reporting date. The Company's reserve projections are based primarily on detailed analysis of the facts in each case, the Company's experience with similar cases and various historical development patterns. Consideration is given to historical patterns such as claim reserving trends and settlement practices, loss payments, pending levels of unpaid claims and product mix, as well as court decisions and economic conditions, including inflation, and public attitudes. All of these factors can affect the estimation of claim and claim adjustment expense reserves. Establishing claim and claim adjustment expense reserves, including claim and claim adjustment expense reserves for catastrophic events that have occurred, is an estimation process. Many factors can ultimately affect the final settlement of a claim and, therefore, the necessary reserve. Changes in the law, results of litigation, medical costs, the cost of repair materials and labor rates can affect ultimate claim costs. In addition, time can be a critical part of reserving determinations since the longer the span between the incidence of a loss and the payment or settlement of the claim, the more variable the ultimate settlement amount can be. Accordingly, short-tail claims, such as property damage claims, tend to be more reasonably estimable than long-tail claims, such as workers' compensation, general liability and professional liability claims. Adjustments to prior year reserve estimates, if necessary, are reflected in the results of operations in the period that the need for such adjustments is determined. There can be no assurance that the Company's ultimate cost for insurance losses will not exceed current estimates. Liability for Unpaid Claim and Claim Adjustment Expenses The table below reconciles the net liability for unpaid claim and claim adjustment expenses to the amount presented in the Consolidated Balance Sheets. As of December 31 (In millions) 2018 Net liability for unpaid claim and claim adjustment expenses: Specialty $ 4,831 Commercial 7,998 International 1,524 Corporate & Other 192 Life & Group (1) 3,420 Total net claim and claim adjustment expenses 17,965 Reinsurance receivables: (2) Specialty 634 Commercial 745 International 226 Corporate & Other (3) 2,233 Life & Group 181 Total reinsurance receivables 4,019 Total gross liability for unpaid claim and claim adjustment expenses $ 21,984 (1) The Life & Group segment amounts are primarily related to long term care claim reserves, but also includes amounts related to unfunded structured settlements arising from short duration contracts. Long term care policies are long duration contracts. (2) Reinsurance receivables presented do not include reinsurance receivables related to paid losses. (3) The Corporate & Other Reinsurance receivables are primarily related to A&EP claims covered under the Loss Portfolio Transfer. The following table presents a reconciliation between beginning and ending claim and claim adjustment expense reserves, including claim and claim adjustment expense reserves of the Life & Group segment. As of or for the years ended December 31 (In millions) 2018 2017 2016 Reserves, beginning of year: Gross $ 22,004 $ 22,343 $ 22,663 Ceded 3,934 4,094 4,087 Net reserves, beginning of year 18,070 18,249 18,576 Net incurred claim and claim adjustment expenses: Provision for insured events of current year 5,358 5,201 5,025 Decrease in provision for insured events of prior years (179 ) (381 ) (342 ) Amortization of discount 176 179 175 Total net incurred (1) 5,355 4,999 4,858 Net payments attributable to: Current year events (1,046 ) (975 ) (967 ) Prior year events (4,285 ) (4,366 ) (4,167 ) Total net payments (5,331 ) (5,341 ) (5,134 ) Foreign currency translation adjustment and other (129 ) 163 (51 ) Net reserves, end of year 17,965 18,070 18,249 Ceded reserves, end of year 4,019 3,934 4,094 Gross reserves, end of year $ 21,984 $ 22,004 $ 22,343 (1) Total net incurred above does not agree to Insurance claims and policyholders' benefits as reflected on the Consolidated Statements of Operations due to amounts related to retroactive reinsurance deferred gain accounting, uncollectible reinsurance and loss deductible receivables, and benefit expenses related to future policy benefits, which are not reflected in the table above. Reserving Methodology In developing claim and claim adjustment expense (“loss” or “losses”) reserve estimates, the Company's actuaries perform detailed reserve analyses that are staggered throughout the year. Every reserve group is reviewed at least once during the year, but most are reviewed more frequently. The analyses generally review losses gross of ceded reinsurance and apply the ceded reinsurance terms to the gross estimates to establish estimates net of reinsurance. Factors considered include, but are not limited to, the historical pattern and volatility of the actuarial indications, the sensitivity of the actuarial indications to changes in paid and incurred loss patterns, the consistency of claims handling processes, the consistency of case reserving practices, changes in the Company's pricing and underwriting, pricing and underwriting trends in the insurance market and legal, judicial, social and economic trends. In addition to the detailed analyses, the Company reviews actual loss emergence for all products each quarter. In developing the loss reserve estimates for property and casualty contracts, the Company generally projects ultimate losses using several common actuarial methods as listed below. The Company reviews the various indications from the various methods and applies judgment to select an actuarial point estimate. The carried reserve may differ from the actuarial point estimate as the result of the Company's consideration of the factors noted above as well as the potential volatility of the projections associated with the specific product being analyzed and other factors affecting claims costs that may not be quantifiable through traditional actuarial analysis. The indicated required reserve is the difference between the selected ultimate loss and the inception-to-date paid losses. The difference between the selected ultimate loss and the case incurred or reported loss is IBNR. IBNR includes a provision for development on known cases as well as a provision for late reported incurred claims. Further, the Company does not establish case reserves for allocated loss adjustment expenses (ALAE), therefore ALAE reserves are included in the Company's estimate of IBNR. The most frequently utilized methods to project ultimate losses include the following: • Paid development: The paid development method estimates ultimate losses by reviewing paid loss patterns and applying them to accident years with further expected changes in paid loss. • Incurred development: The incurred development method is similar to the paid development method, but it uses case incurred losses instead of paid losses. • Loss ratio: The loss ratio method multiplies premiums by an expected loss ratio to produce ultimate loss estimates for each accident year. • Bornhuetter-Ferguson using premiums and paid loss: The Bornhuetter-Ferguson using premiums and paid loss method is a combination of the paid development approach and the loss ratio approach. This method normally determines expected loss ratios similar to the approach used to estimate the expected loss ratio for the loss ratio method. • Bornhuetter-Ferguson using premiums and incurred loss: The Bornhuetter-Ferguson using premiums and incurred loss method is similar to the Bornhuetter-Ferguson using premiums and paid loss method except that it uses case incurred losses. • Frequency times severity: The frequency times severity method multiplies a projected number of ultimate claims by an estimated ultimate average loss for each accident year to produce ultimate loss estimates. • Stochastic modeling: The stochastic modeling produces a range of possible outcomes based on varying assumptions related to the particular product being modeled. For many exposures, especially those that can be considered long-tail, a particular accident or policy year may not have a sufficient volume of paid losses to produce a statistically reliable estimate of ultimate losses. In such a case, the Company's actuaries typically assign more weight to the incurred development method than to the paid development method. As claims continue to settle and the volume of paid loss increases, the actuaries may assign additional weight to the paid development method. For most of the Company's products, even the incurred losses for accident or policy years that are early in the claim settlement process will not be of sufficient volume to produce a reliable estimate of ultimate losses. In these cases, the Company may not assign any weight to the paid and incurred development methods. The Company will use the loss ratio, Bornhuetter-Ferguson and frequency times severity methods. For short-tail exposures, the paid and incurred development methods can often be relied on sooner, primarily because the Company's history includes a sufficient number of years to cover the entire period over which paid and incurred losses are expected to change. However, the Company may also use the loss ratio, Bornhuetter-Ferguson and frequency times severity methods for short-tail exposures. For other more complex reserve groups where the above methods may not produce reliable indications, the Company uses additional methods tailored to the characteristics of the specific situation. Certain claim liabilities are more difficult to estimate or have differing methodologies and considerations which are described below. Mass Tort and A&EP Reserves The Company's reserving methodologies for mass tort and A&EP are similar as both are based on detailed reviews of large accounts with estimates of ultimate payments based on the facts in each case and the Company's view of applicable law and coverage litigation. Life & Group The Life & Group segment includes the run-off long term care business as well as structured settlement obligations not funded by annuities related to certain property and casualty claimants. Long term care policies provide benefits for nursing homes, assisted living facilities and home health care subject to various daily and lifetime caps. Generally, policyholders must continue to make periodic premium payments to keep the policy in force and we have the ability to increase policy premiums, subject to state regulatory approval. The Company maintains both claim and claim adjustment expense reserves as well as future policy benefit reserves for policyholder benefits for the Life & Group segment. Claim and claim adjustment expense reserves consist of estimated reserves for long term care policyholders that are currently receiving benefits, including claims that have been incurred but are not yet reported. In developing the claim and claim adjustment expense reserve estimates for the long term care policies, the Company's actuaries perform a detailed claim experience study on an annual basis. The study reviews the sufficiency of existing reserves for policyholders currently on claim and includes an evaluation of expected benefit utilization and claim duration. The Company's recorded claim and claim adjustment expense reserves reflect management's best estimate after incorporating the results of the most recent study. In addition, claim and claim adjustment expense reserves are also maintained for the structured settlement obligations. Both elements of the Life & Group reserves are discounted as discussed in Note A to the Consolidated Financial Statements. Gross and Net Carried Reserves The following tables present the gross and net carried reserves. December 31, 2018 Specialty Commercial International Life & Group Corporate & Other Total (In millions) Gross Case Reserves $ 1,623 $ 4,181 $ 867 $ 3,516 $ 1,208 $ 11,395 Gross IBNR Reserves 3,842 4,562 883 85 1,217 10,589 Total Gross Carried Claim and Claim Adjustment Expense Reserves $ 5,465 $ 8,743 $ 1,750 $ 3,601 $ 2,425 $ 21,984 Net Case Reserves $ 1,483 $ 3,831 $ 749 $ 3,364 $ 96 $ 9,523 Net IBNR Reserves 3,348 4,167 775 56 96 8,442 Total Net Carried Claim and Claim Adjustment Expense Reserves $ 4,831 $ 7,998 $ 1,524 $ 3,420 $ 192 $ 17,965 December 31, 2017 Specialty Commercial International Life & Group Corporate & Other Total (In millions) Gross Case Reserves $ 1,742 $ 4,427 $ 744 $ 3,386 $ 1,371 $ 11,670 Gross IBNR Reserves 3,927 4,337 892 113 1,065 10,334 Total Gross Carried Claim and Claim Adjustment Expense Reserves $ 5,669 $ 8,764 $ 1,636 $ 3,499 $ 2,436 $ 22,004 Net Case Reserves $ 1,600 $ 4,103 $ 640 $ 3,208 $ 94 $ 9,645 Net IBNR Reserves 3,407 4,033 792 82 111 8,425 Total Net Carried Claim and Claim Adjustment Expense Reserves $ 5,007 $ 8,136 $ 1,432 $ 3,290 $ 205 $ 18,070 Net Prior Year Development Changes in estimates of claim and claim adjustment expense reserves, net of reinsurance, for prior years are defined as net prior year loss reserve development (development). These changes can be favorable or unfavorable. The following table presents development recorded for the Specialty, Commercial, International and Corporate & Other segments. December 31, 2018 (In millions) 2018 2017 2016 Pretax (favorable) unfavorable development: Specialty $ (150 ) $ (174 ) $ (247 ) Commercial (25 ) (115 ) 15 International (4 ) (9 ) (58 ) Corporate & Other (2 ) (10 ) 2 Total pretax (favorable) unfavorable development $ (181 ) $ (308 ) $ (288 ) Favorable net prior year loss reserve development of $19 million , $72 million and $46 million was recorded in the Life & Group segment for the years ended December 31, 2018 , 2017 and 2016 . The favorable net prior year loss reserve development for the year ended December 31, 2018 was driven by lower than expected claim severity. Segment Development Tables For the Specialty, Commercial and International segments, the following tables present further detail and commentary on the development reflected in the financial statements for each of the periods presented. Also presented are loss reserve development tables that illustrate the change over time of reserves established for claim and allocated claim adjustment expenses arising from short duration insurance contracts for certain lines of business within each of these segments. Not all lines of business or segments are presented based on their context to the Company's overall loss reserves, calendar year reserve development, or calendar year net earned premiums. Insurance contracts are considered to be short duration contracts when the contracts are not expected to remain in force for an extended period of time. The Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses tables, reading across, show the cumulative net incurred claim and allocated claim adjustment expenses relating to each accident year at the end of the stated calendar year. Changes in the cumulative amount across time are the result of the Company's expanded awareness of additional facts and circumstances that pertain to the unsettled claims. The Cumulative Net Paid Claims and Allocated Claim Adjustment Expenses tables, reading across, show the cumulative amount paid for claims in each accident year as of the end of the stated calendar year. The Net Strengthening or (Releases) of Prior Accident Year Reserves tables, reading across, show the net increase or decrease in the cumulative net incurred accident year claim and allocated claim adjustment expenses during each stated calendar year and indicates whether the reserves for that accident year were strengthened or released. The information in the tables is reported on a net basis after reinsurance and does not include the effects of discounting. The information contained in calendar years 2017 and prior is unaudited. Information contained in the tables pertaining to the Company's International segment has been presented at the year-end 2018 foreign currency exchange rates for all periods presented to remove the effects of foreign currency exchange rate changes between calendar years. The Company has presented development information for the Hardy business prospectively from the date of acquisition and is presented as a separate table within the Company's International segment. To the extent the Company enters into a commutation, the transaction is reported on a prospective basis. To the extent that the Company enters into a disposition, the effects of the disposition are reported on a retrospective basis by removing the balances associated with the disposed of business. The amounts reported for the cumulative number of reported claims include direct and assumed open and closed claims by accident year at the claimant level. The number excludes claim counts for claims within a policy deductible where the insured is responsible for payment of losses in the deductible layer. Claim count data for certain assumed reinsurance contracts is unavailable. IBNR includes reserves for incurred but not reported losses and expected development on case reserves. The Company does not establish case reserves for ALAE, therefore ALAE reserves are also included in the estimate of IBNR. Specialty The following table presents further detail of the development recorded for the Specialty segment. Years ended December 31 (In millions) 2018 2017 2016 Pretax (favorable) unfavorable development: Medical Professional Liability $ 47 $ 30 $ 9 Other Professional Liability and Management Liability (127 ) (126 ) (140 ) Surety (70 ) (84 ) (63 ) Warranty (10 ) 4 4 Other 10 2 (57 ) Total pretax (favorable) unfavorable development $ (150 ) $ (174 ) $ (247 ) 2018 Unfavorable development in medical professional liability was primarily due to higher than expected severity in accident years 2014 and 2017 in our hospitals business. Additionally, there was higher than expected frequency and severity in aging services in accident years 2014 through 2017 combined, partially offset by lower than expected frequency in accident year 2015. Favorable development in other professional liability and management liability was primarily due to lower than expected claim frequency in recent accident years related to financial institutions and professional liability errors and omissions (E&O), favorable severity in accident years 2015 and prior related to professional liability E&O and favorable outcomes on individual claims in financial institutions in accident years 2013 and prior. Favorable development in surety was due to lower than expected loss emergence for accident years 2017 and prior. 2017 Unfavorable development in medical professional liability was primarily due to continued higher than expected frequency in aging services and higher than expected severity for hospitals in recent accident years. This was partially offset by favorable development in hospitals in prior accident years as well as favorable development related to unallocated claim adjustment expenses. Favorable development in other professional liability and management liability was primarily due to favorable settlements on closed claims and a lower frequency of large losses for accident years 2011 through 2015 for professional and management liability, lower than expected claim frequency in accident years 2012 through 2015 for professional liability and lower than expected severity in accident years 2014 through 2015 for professional liability. Favorable development in surety coverages was primarily due to lower than expected frequency of large losses in accident years 2015 and prior. 2016 Favorable development in other professional liability and management liability was primarily due to favorable settlements on closed claims and lower than expected frequency of claims in accident years 2010 through 2014 related to professional services and financial institutions. This was partially offset by unfavorable development related to a specific financial institutions claim in accident year 2014, higher management liability severities in accident year 2015 and deterioration on credit crises-related claims in accident year 2009. Favorable development in surety coverages was primarily due to lower than expected frequency of large losses in accident years 2014 and prior. Favorable development in other coverages provided to Specialty customers was due to better than expected claim frequency and claim severity in commercial lines coverages in accident years 2010 through 2015. Specialty - Line of Business Composition The table below provides the line of business composition of the net liability for unpaid claim and claim adjustment expenses for the Specialty segment. As of December 31 (In millions) 2018 Net liability for unpaid claim and claim adjustment expenses: Medical Professional Liability $ 1,457 Other Professional Liability and Management Liability 2,849 Surety 379 Warranty 40 Other 106 Total net liability for unpaid claim and claim adjustment expenses $ 4,831 Specialty - Medical Professional Liability Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses are presented in the following table. As of December 31 Calendar Year As of December 31, 2018 (In millions, except reported claims data) 2009 (1) 2010 (1) 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 IBNR Cumulative Number of Claims Accident Year 2009 $ 389 $ 390 $ 392 $ 392 $ 366 $ 346 $ 336 $ 309 $ 302 $ 310 $ — 14,716 2010 402 412 423 426 415 395 365 360 356 — 14,615 2011 429 437 443 468 439 434 437 437 8 16,505 2012 464 469 508 498 493 484 493 10 17,691 2013 462 479 500 513 525 535 28 19,442 2014 450 489 537 530 535 30 19,602 2015 433 499 510 494 78 17,835 2016 427 487 485 120 15,427 2017 412 449 217 13,777 2018 404 333 11,205 Total $ 4,498 $ 824 Cumulative Net Paid Claims and Allocated Claim Adjustment Expenses are presented in the following table. As of December 31 Calendar Year (In millions) 2009 (1) 2010 (1) 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 Accident Year 2009 $ 9 $ 63 $ 143 $ 211 $ 247 $ 269 $ 280 $ 288 $ 291 $ 300 2010 10 86 173 257 306 326 337 346 350 2011 17 109 208 295 347 375 398 409 2012 14 117 221 323 388 427 457 2013 17 119 255 355 414 462 2014 23 136 258 359 417 2015 22 101 230 313 2016 18 121 246 2017 19 107 2018 21 Total $ 3,082 Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented $ 1,416 Net liability for unpaid claim and claim adjustment expenses for accident years prior to 2009 18 Liability for unallocated claim adjustment expenses for accident years presented 23 Total net liability for unpaid claim and claim adjustment expenses $ 1,457 Net strengthening or (releases) of prior accident year reserves is presented in the following table. For the years ended December 31 Calendar Year (In millions) 2010 (1) 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 Total Accident Year 2009 $ 1 $ 2 $ — $ (26 ) $ (20 ) $ (10 ) $ (27 ) $ (7 ) $ 8 $ (79 ) 2010 10 11 3 (11 ) (20 ) (30 ) (5 ) (4 ) (46 ) 2011 8 6 25 (29 ) (5 ) 3 — 8 2012 5 39 (10 ) (5 ) (9 ) 9 29 2013 17 21 13 12 10 73 2014 39 48 (7 ) 5 85 2015 66 11 (16 ) 61 2016 60 (2 ) 58 2017 37 37 Total net development for the accident years presented above 60 58 47 Total net development for accident years prior to 2009 (51 ) (21 ) 1 Total unallocated claim adjustment expense development — (7 ) (1 ) Total $ 9 $ 30 $ 47 (1) Data presented for these calendar years is required supplemental information, which is unaudited. Specialty - Other Professional Liability and Management Liability Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses are presented in the following table. As of December 31 Calendar Year As of December 31, 2018 (In millions, except reported claims data) 2009 (1) 2010 (1) 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 IBNR Cumulative Number of Claims Accident Year 2009 $ 831 $ 875 $ 908 $ 903 $ 893 $ 903 $ 897 $ 906 $ 904 $ 892 $ 18 17,374 2010 828 828 848 848 847 837 824 827 821 19 17,888 2011 880 908 934 949 944 911 899 888 39 18,728 2012 923 909 887 878 840 846 833 41 18,491 2013 884 894 926 885 866 863 65 17,918 2014 878 898 885 831 835 88 17,515 2015 888 892 877 832 194 17,333 2016 901 900 900 279 17,787 2017 847 845 479 17,780 2018 850 726 16,564 Total $ 8,559 $ 1,948 Cumulative Net Paid Claims and Allocated Claim Adjustment Expenses are presented in the following table. As of December 31 Calendar Year (In millions) 2009 (1) 2010 (1) 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 Accident Year 2009 $ 37 $ 195 $ 361 $ 553 $ 641 $ 722 $ 772 $ 801 $ 825 $ 844 2010 31 204 405 541 630 670 721 752 784 2011 71 314 503 605 683 726 781 796 2012 56 248 400 573 651 711 755 2013 54 249 447 618 702 754 2014 51 223 392 515 647 2015 60 234 404 542 2016 64 248 466 2017 57 222 2018 54 Total $ 5,864 Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented $ 2,695 Net liability for unpaid claim and claim adjustment expenses for accident years prior to 2009 90 Liability for unallocated claim adjustment expenses for accident years presented 64 Total net liability for unpaid claim and claim adjustment expenses $ 2,849 Net strengthening or (releases) of prior accident year reserves is presented in the following table. For the years ended December 31 Calendar Year (In millions) 2010 (1) 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 Total Accident Year 2009 $ 44 $ 33 $ (5 ) $ (10 ) $ 10 $ (6 ) $ 9 $ (2 ) $ (12 ) $ 61 2010 — 20 — (1 ) (10 ) (13 ) 3 (6 ) (7 ) 2011 28 26 15 (5 ) (33 ) (12 ) (11 ) 8 2012 (14 ) (22 ) (9 ) (38 ) 6 (13 ) (90 ) 2013 10 32 (41 ) (19 ) (3 ) (21 ) 2014 20 (13 ) (54 ) 4 (43 ) 2015 4 (15 ) (45 ) (56 ) 2016 (1 ) — (1 ) 2017 (2 ) (2 ) Total net development for the accident years presented above (125 ) (94 ) (88 ) Total net development for accident years prior to 2009 (15 ) (25 ) (32 ) Total unallocated claim adjustment expense development — (7 ) (7 ) Total $ (140 ) $ (126 ) $ (127 ) (1) Data presented for these calendar years is required supplemental information, which is unaudited. Specialty - Surety Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses are presented in the following table. As of December 31 Calendar Year As of December 31, 2018 (In millions, except reported claims data) 2009 (1) 2010 (1) 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 IBNR Cumulative Number of Claims Accident Year 2009 $ 114 $ 114 $ 103 $ 85 $ 68 $ 59 $ 52 $ 53 $ 53 $ 52 $ 1 6,688 2010 112 112 111 84 76 66 63 59 61 1 5,971 2011 120 121 116 87 75 70 66 62 1 5,808 2012 120 122 98 70 52 45 39 2 5,559 2013 120 121 115 106 91 87 6 5,039 2014 123 124 94 69 60 19 5,036 2015 131 131 104 79 36 4,887 2016 124 124 109 60 5,185 2017 120 115 78 4,936 2018 114 101 3,105 Total $ 778 $ 305 Cumulative Net Paid Claims and Allocated Claim Adjustment Expenses are presented in the following table. As of December 31 Calendar Year (In millions) 2009 (1) 2010 (1) 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 Accident Year 2009 $ 13 $ 24 $ 34 $ 41 $ 43 $ 45 $ 46 $ 47 $ 47 $ 47 2010 13 34 50 55 57 58 55 52 52 2011 19 42 55 58 60 60 56 57 2012 5 32 34 35 35 36 37 2013 16 40 69 78 78 78 2014 7 30 38 36 38 2015 7 26 38 40 2016 5 37 45 2017 23 37 2018 5 Total $ 436 Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented $ 342 Net liability for unpaid claim and claim adjustment expenses for accident years prior to 2009 7 Liability for unallocated claim adjustment expenses for accident years presented 30 Total net liability for unpaid claim and claim adjustment expenses $ 379 Net strengthening or (releases) of prior accident year reserves is presented in the following table. For the years ended December 31 Calendar Year (In millions) 2010 (1) 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 Total Accident Year 2009 $ — $ (11 ) $ (18 ) $ (17 ) $ (9 ) $ (7 ) $ 1 $ — $ (1 ) $ (62 ) 2010 — (1 ) (27 ) (8 ) (10 ) (3 ) (4 ) 2 (51 ) 2011 1 (5 ) (29 ) (12 ) (5 ) (4 ) (4 ) (58 ) 2012 2 (24 ) (28 ) (18 ) (7 ) (6 ) (81 ) 2013 1 (6 ) (9 ) (15 ) (4 ) (33 ) 2014 1 (30 ) (25 ) (9 ) (63 ) 2015 — (27 ) (25 ) (52 ) 2016 — (15 ) (15 ) 2017 (5 ) (5 ) Total net development for the accident years presented above (64 ) (82 ) (67 ) Total net development for accident years prior to 2009 1 1 (3 ) Total unallocated claim adjustment expense development — (3 ) — Total $ (63 ) $ (84 ) $ (70 ) (1) Data presented for these calendar years is required supplemental information, which is unaudited. Commercial The following table presents further detail of the development recorded for the Commercial segment. Years ended December 31 (In millions) 2018 2017 2016 Pretax (favorable) unfavorable development: Commercial Auto $ 1 $ (35 ) $ (47 ) General Liability 32 (24 ) (65 ) Workers' Compensation (32 ) (63 ) 145 Property and Other (26 ) 7 (18 ) Total pretax (favorable) unfavorable development $ (25 ) $ (115 ) $ 15 2018 Unfavorable development in general liability was driven by higher than expected claim severity in unsupported umbrella in accident years 2013 through 2016. Favorable development in workers’ compensation was driven by lower frequency and severity experience and favorable impacts from California reforms. Favorable development in property and other was driven by lower than expected claim severity in catastrophes in accident year 2017. 2017 Favorable development in commercial auto was primarily due to lower than expected severity in accident years 2013 through 2016, as well as a large favorable recovery on a claim in accident year 2012. Favorable development in general liability was due to lower than expected severity in life sciences. Favorable development in workers’ compensation was primarily related to decreases in frequency and severity in recent accident years, partially attributable to California reforms impacting medical costs. This was partially offset by unfavorable development related to an adverse arbitration ruling on reinsurance recoverables from older accident years as well as the recognition of loss estimates associated with earned premium from a prior exposure year. 2016 Favorable development in commercial auto was primarily due to favorable settlements on claims in accident years 2010 through 2014 and lower than expected severities in accident years 2012 through 2015. Favorable development in general liability was primarily due to better than expected claim settlements in accident years 2012 through 2014, better than expected severity on umbrella claims in accident years 2010 through 2013, and better than expected severity in medical products liability in accident years 2010 through 2015. This was partially offset by unfavorable development related to an increase in reported claims prior to the closing of the three year window set forth by the Minnesota Child Victims Act in accident years 2006 and prior. Unfavorable development in workers' compensation was primarily due to higher than expected severity for Defense Base Act contractors that largely resulted from a reduction of expected future recoveries from the US Department of Labor under the War Hazard Act. Further unfavorable development was due to the impact of recent Florida court rulings for accident years 2008 through 2015. These were partially offset by favorable development related to lower than expected frequencies related to our ongoing Middle Market and Small Business results for accident years 2009 through 2014. Favorable development in property and other was primarily due to better than expected loss frequency in accident years 2013 through 2015. This was partially offset by unfavorable development related to higher than expected severity from a fourth quarter 2015 catastrophe event. Commercial - Line of Business Composition The table below provides the line of business composition of the net liability for unpaid claim and claim adjustment expenses for the Commercial segment. As of December 31 (In millions) 2018 Net Claim and claim adjustment expenses: Commercial Auto $ 412 General Liability 3,195 Workers' Compensation 3,968 Property and Other 423 Total net liability for claim and claim adjustment expenses $ 7,998 Commercial - Commercial Auto Cumulative Net Incurred Claim and Allocated C

Legal Proceedings, Contingencie

Legal Proceedings, Contingencies and Guarantees	12 Months Ended
	Dec. 31, 2018
Legal Proceedings, Commitments and Contingencies, and Guarantees [Abstract]
Legal Proceedings, Contingencies and Guarantees	Legal Proceedings, Contingencies and Guarantees Small Business Premium Rate Adjustment In 2016 and 2017, the Company identified rating errors related to its multi-peril package product and workers' compensation policies within its Small Business unit and determined that it would voluntarily issue premium refunds along with interest on affected policies. After the rating errors were identified, written and earned premium were reported net of any impact from the premium rate adjustments. The policyholder refunds for the multi-peril package product were completed in the third quarter of 2017 . The policyholder refunds for workers’ compensation policies were completed in the fourth quarter of 2018 . For the year ended December 31, 2016 , the Company recorded a charge which reduced earned premium by $16 million . For the year ended December 31, 2017 , earned premium was reduced by $36 million . For the year ended December 31, 2018 , earned premium increased by $6 million as a result of a change in estimate of the refund payments to policyholders. Additionally, Interest expense recognized for interest due to policyholders on the premium rate adjustments was $1 million and $7 million for the years ended December 31, 2018 and 2017 . Other Litigation The Company is a party to other routine litigation incidental to its business, which, based on the facts and circumstances currently known, is not material to the Company's results of operations or financial position. Guarantees As of December 31, 2018 and 2017 , the Company had recorded liabilities of approximately $5 million related to guarantee and indemnification agreements and management does not believe that any future indemnity claims will be significantly greater than the amounts recorded. In the course of selling business entities and assets to third parties, the Company agreed to guarantee the performance of certain obligations of previously owned subsidiaries and to indemnify purchasers for losses arising out of breaches of representation and warranties with respect to the business entities or assets sold, including, in certain cases, losses arising from undisclosed liabilities or certain named litigation. Such guarantee and indemnification agreements in effect for sales of business entities, assets and third-party loans may include provisions that survive indefinitely. As of December 31, 2018 , the aggregate amount related to quantifiable guarantees was $375 million and the aggregate amount related to quantifiable indemnification agreements was $252 million . In certain cases, should the Company be required to make payments under any such guarantee, it would have the right to seek reimbursement from an affiliate of a previously owned subsidiary. In addition, the Company has agreed to provide indemnification to third-party purchasers for certain losses associated with sold business entities or assets that are not limited by a contractual monetary amount. As of December 31, 2018 , the Company had outstanding unlimited indemnifications in connection with the sales of certain of its business entities or assets that included tax liabilities arising prior to a purchaser's ownership of an entity or asset, defects in title at the time of sale, employee claims arising prior to closing and in some cases losses arising from certain litigation and undisclosed liabilities. Certain provisions of the indemnification agreements survive indefinitely, while others survive until the applicable statutes of limitation expire, or until the agreed-upon contract terms expire. The Company also provided guarantees, if the primary obligor fails to perform, to holders of structured settlement annuities provided by a previously owned subsidiary. As of December 31, 2018 , the potential amount of future payments the Company could be required to pay under these guarantees was approximately $1.8 billion , which will be paid over the lifetime of the annuitants. The Company does not believe any payment is likely under these guarantees, as the Company is the beneficiary of a trust that must be maintained at a level that approximates the discounted reserves for these annuities.

Reinsurance

Reinsurance	12 Months Ended
	Dec. 31, 2018
Reinsurance Disclosures [Abstract]
Reinsurance	Reinsurance The Company cedes insurance to reinsurers to limit its maximum loss, provide greater diversification of risk, minimize exposures on larger risks and to exit certain lines of business. The ceding of insurance does not discharge the primary liability of the Company. A credit exposure exists with respect to reinsurance ceded to the extent that any reinsurer is unable to meet its obligations. A collectibility exposure also exists to the extent that the reinsurer disputes the liabilities assumed under reinsurance agreements. Property and casualty reinsurance coverages are tailored to the specific risk characteristics of each product line and the Company's retained amount varies by type of coverage. Reinsurance contracts are purchased to protect specific lines of business such as property and workers' compensation. Corporate catastrophe reinsurance is also purchased for property and workers' compensation exposure. The Company also utilizes facultative reinsurance in certain lines. In addition, the Company assumes reinsurance primarily through Hardy and as a member of various reinsurance pools and associations. The following table presents the amounts receivable from reinsurers. December 31 (In millions) 2018 2017 Reinsurance receivables related to insurance reserves: Ceded claim and claim adjustment expenses $ 4,019 $ 3,934 Ceded future policy benefits 233 230 Reinsurance receivables related to paid losses 203 126 Reinsurance receivables 4,455 4,290 Allowance for uncollectible reinsurance (29 ) (29 ) Reinsurance receivables, net of allowance for uncollectible reinsurance $ 4,426 $ 4,261 The Company has established an allowance for uncollectible reinsurance receivables related to credit risk. The Company reviews the allowance quarterly and adjusts the allowance as necessary to reflect changes in estimates of uncollectible balances. The allowance may also be reduced by write-offs of reinsurance receivable balances. The Company attempts to mitigate its credit risk related to reinsurance by entering into reinsurance arrangements with reinsurers that have credit ratings above certain levels and by obtaining collateral. On a limited basis, the Company may enter into reinsurance agreements with reinsurers that are not rated, primarily captive reinsurers. The primary methods of obtaining collateral are through reinsurance trusts, letters of credit and funds withheld balances. Such collateral was approximately $3.2 billion and $2.9 billion as of December 31, 2018 and 2017 . The Company's largest recoverables from a single reinsurer as of December 31, 2018 , including ceded unearned premium reserves, were approximately $2.2 billion from a subsidiary of Berkshire Hathaway Insurance Group, $278 million from the Gateway Rivers Insurance Company and $233 million from subsidiaries of Wilton Re. These amounts are substantially collateralized. The recoverable from the Berkshire Hathaway Insurance Group includes amounts related to third-party reinsurance for which NICO has assumed the credit risk under the terms of the LPT as discussed in Note E to the Consolidated Financial Statements. The effects of reinsurance on earned premiums and written premiums are presented in the following tables. (In millions) Direct Assumed Ceded Net Assumed/ Net % 2018 Earned Premiums Property and casualty $ 10,857 $ 305 $ 4,380 $ 6,782 4.5 % Long term care 480 50 — 530 9.4 % Total earned premiums $ 11,337 $ 355 $ 4,380 $ 7,312 4.9 % 2017 Earned Premiums Property and casualty $ 10,447 $ 317 $ 4,315 $ 6,449 4.9 % Long term care 489 50 — 539 9.3 % Total earned premiums $ 10,936 $ 367 $ 4,315 $ 6,988 5.3 % 2016 Earned Premiums Property and casualty $ 10,400 $ 258 $ 4,270 $ 6,388 4.0 % Long term care 486 50 — 536 9.3 % Total earned premiums $ 10,886 $ 308 $ 4,270 $ 6,924 4.4 % (In millions) Direct Assumed Ceded Net Assumed/ Net % 2018 Written Premiums Property and casualty $ 11,094 $ 310 $ 4,583 $ 6,821 4.5 % Long term care 474 50 — 524 9.5 % Total written premiums $ 11,568 $ 360 $ 4,583 $ 7,345 4.9 % 2017 Written Premiums Property and casualty $ 10,655 $ 327 $ 4,449 $ 6,533 5.0 % Long term care 486 50 — 536 9.3 % Total written premiums $ 11,141 $ 377 $ 4,449 $ 7,069 5.3 % 2016 Written Premiums Property and casualty $ 10,451 $ 245 $ 4,255 $ 6,441 3.8 % Long term care 495 52 — 547 9.5 % Total written premiums $ 10,946 $ 297 $ 4,255 $ 6,988 4.3 % Included in the direct and ceded earned premiums for the years ended December 31, 2018 , 2017 and 2016 are $3,740 million , $3,864 million and $3,865 million related to property business that is 100% reinsured under a significant third-party captive program. The third-party captives that participate in this program are affiliated with the non-insurance company policyholders, therefore this program provides a means for the policyholders to self-insure this property risk. The Company receives and retains a ceding commission. Long term care premiums are from long duration contracts; property and casualty premiums are from short duration contracts. Insurance claims and policyholders' benefits reported on the Consolidated Statements of Operations are net of reinsurance recoveries of $2,836 million , $3,085 million and $3,016 million for the years ended December 31, 2018 , 2017 and 2016 , including $1,927 million , $2,541 million and $2,621 million , respectively, related to the significant third-party captive program discussed above.

Debt

Debt	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Debt	Debt Debt is composed of the following obligations. December 31 (In millions) 2018 2017 Short term debt: Senior notes of CNAF, 6.950%, face amount of $150, due January 15, 2018 $ — $ 150 Long term debt: Senior notes of CNAF: 5.875%, face amount of $500, due August 15, 2020 499 498 5.750%, face amount of $400, due August 15, 2021 399 398 3.950%, face amount of $550, due May 15, 2024 547 547 4.500%, face amount of $500, due March 1, 2026 498 498 3.450%, face amount of $500, due August 15, 2027 495 495 Debenture of CNAF, 7.250%, face amount of $243, due November 15, 2023 242 242 Subordinated variable rate debt of Hardy, face amount of $30, due September 15, 2036 (1) — 30 Total long term debt 2,680 2,708 Total debt $ 2,680 $ 2,858 (1) In the third quarter of 2018, the Company redeemed $30 million of subordinated variable rate debt of Hardy due September 15, 2036. CCC is a member of the FHLBC. FHLBC membership provides participants with access to additional sources of liquidity through various programs and services. As a requirement of membership in the FHLBC, CCC held $5 million of FHLBC stock as of December 31, 2018 giving it immediate access to approximately $111 million of additional liquidity. As of December 31, 2018 and 2017 , CCC had no outstanding borrowings from the FHLBC. During 2015, the Company entered into a five -year $250 million senior unsecured revolving credit facility with a syndicate of banks which may be used for general corporate purposes. The credit agreement includes several covenants, including maintenance of a minimum consolidated net worth and a defined ratio of consolidated indebtedness to consolidated total capitalization. The minimum consolidated net worth, as defined as of December 31, 2018 , was $8.7 billion . As of December 31, 2018 and 2017 , the Company had no outstanding borrowings under the credit agreement. The Company's debt obligations contain customary covenants for investment grade issuers. The Company was in compliance with all covenants as of and for the years ended December 31, 2018 and 2017 . The combined aggregate maturities for debt as of December 31, 2018 are presented in the following table. (In millions) 2019 $ — 2020 500 2021 400 2022 — 2023 243 Thereafter 1,550 Less discount (13 ) Total $ 2,680

Benefit Plans

Benefit Plans	12 Months Ended
	Dec. 31, 2018
Retirement Benefits [Abstract]
Benefit Plans	Benefit Plans Pension and Postretirement Health Care Benefit Plans CNA sponsors noncontributory defined benefit pension plans, primarily through the CNA Retirement Plan, covering certain eligible employees. These plans are closed to new entrants. CNA's funding policy for defined benefit pension plans is to make contributions in accordance with applicable governmental regulatory requirements with consideration of the funded status of the plans. Effective January 1, 2000, the CNA Retirement Plan was closed to new participants. Existing participants at that time were given a choice to either continue to accrue benefits under the CNA Retirement Plan or to cease accruals effective December 31, 1999. Employees who chose to continue to accrue benefits under the plan received benefits in accordance with plan provisions through June 30, 2015 as discussed further below. Employees who elected to cease accruals effective December 31, 1999 received the present value of their accrued benefit in an accrued pension account that is credited with interest based on the annual rate of interest on 30-year Treasury securities. These employees also receive certain enhanced employer contributions in the CNA 401(k) Plus Plan. Effective June 30, 2015, the Company eliminated future benefit accruals associated with the CNA Retirement Plan. Participants continuing to accrue benefits under the CNA Retirement Plan at that time were entitled to an accrued benefit payable based on their eligible compensation and accrued service through June 30, 2015. These employees also began receiving enhanced employer contributions in the CNA 401(k) Plus Plan similar to employees who elected to cease accruals effective December 31, 1999. Employees who elected to cease accruals effective December 31, 1999 were not affected by this curtailment. CNA provides certain health care benefits to eligible retired employees, their covered dependents and their beneficiaries primarily through the CNA Health and Group Benefits Program. These postretirement benefits have largely been eliminated for active employees. The following table presents a reconciliation of benefit obligations and plan assets. Pension Benefits Postretirement Benefits (In millions) 2018 2017 2018 2017 Benefit obligation as of January 1 $ 2,749 $ 2,729 $ 11 $ 15 Changes in benefit obligation: Service cost — — — — Interest cost 93 103 — — Participants' contributions — — 3 4 Actuarial (gain) loss (187 ) 99 — (1 ) Benefits paid (166 ) (170 ) (5 ) (7 ) Foreign currency translation and other (7 ) 10 — — Settlements (16 ) (22 ) — — Benefit obligation as of December 31 2,466 2,749 9 11 Fair value of plan assets as of January 1 2,261 2,193 — — Change in plan assets: Actual return on plan assets (69 ) 221 — — Company contributions 23 29 2 3 Participants' contributions — — 3 4 Benefits paid (166 ) (170 ) (5 ) (7 ) Foreign currency translation and other (8 ) 10 — — Settlements (16 ) (22 ) — — Fair value of plan assets as of December 31 2,025 2,261 — — Funded status $ (441 ) $ (488 ) $ (9 ) $ (11 ) Amounts recognized on the Consolidated Balance Sheets as of December 31: Other assets $ 9 $ 4 $ — $ — Other liabilities (450 ) (492 ) (9 ) (11 ) Net amount recognized $ (441 ) $ (488 ) $ (9 ) $ (11 ) Amounts recognized in Accumulated other comprehensive income, not yet recognized in net periodic cost (benefit): Prior service credit $ — $ — $ — $ (2 ) Net actuarial (gain) loss 984 987 (3 ) (4 ) Net amount recognized $ 984 $ 987 $ (3 ) $ (6 ) The accumulated benefit obligation for all defined benefit pension plans was $2,465 million and $2,749 million as of December 31, 2018 and 2017 . Changes for years ended December 31, 2018 and 2017 include actuarial (gains) losses of $(187) million and $99 million respectively, primarily driven by changes in the discount rate used to determine defined benefit pension obligations. The components of net periodic pension cost (benefit) are presented in the following table. Years ended December 31 (In millions) 2018 2017 2016 Net periodic pension cost (benefit) Service cost $ — $ — $ — Non-service cost (benefit): Interest cost on projected benefit obligation 93 103 113 Expected return on plan assets (159 ) (154 ) (160 ) Amortization of net actuarial (gain) loss 37 35 37 Settlement loss 6 9 — Total non-service cost (benefit) (23 ) (7 ) (10 ) Total net periodic pension cost (benefit) $ (23 ) $ (7 ) $ (10 ) For the years ended December 31, 2018 , 2017 and 2016 , the Company recognized $8 million , $2 million and $3 million of non-service benefit in Insurance claims and policyholders' benefits and $15 million , $5 million and $7 million of non-service benefit in Other operating expenses related to net periodic pension costs (benefit). The components of net periodic postretirement cost (benefit) are presented in the following table. Years ended December 31 (In millions) 2018 2017 2016 Net periodic postretirement cost (benefit) Service cost $ — $ — $ — Non-service cost (benefit): Amortization of prior service credit (1 ) (2 ) (2 ) Amortization of net actuarial (gain) loss (1 ) — — Total non-service cost (benefit) (2 ) (2 ) (2 ) Total net periodic postretirement cost (benefit) $ (2 ) $ (2 ) $ (2 ) For the years ended December 31, 2018 , 2017 and 2016 , the Company recognized $1 million of non-service benefit in Insurance claims and policyholders' benefits and $1 million of non-service benefit in Other operating expenses related to net periodic postretirement cost (benefit), respectively. The amounts recognized in Other comprehensive income are presented in the following table. Years ended December 31 (In millions) 2018 2017 2016 Pension and postretirement benefits Amounts arising during the period $ (41 ) $ (31 ) $ (29 ) Settlement 6 9 (2 ) Reclassification adjustment relating to prior service credit (2 ) (2 ) (2 ) Reclassification adjustment relating to actuarial loss 36 35 37 Total increase (decrease) in Other comprehensive income $ (1 ) $ 11 $ 4 Actuarial assumptions used for the CNA Retirement Plan and CNA Health and Group Benefits Program to determine benefit obligations are presented in the following table. The interest crediting rate is the weighted average interest rate applied to the individual pension balances for employees who elected to cease accruals effective December 31, 1999. December 31 2018 2017 Pension benefits Discount rate 4.250 % 3.550 % Expected long term rate of return 7.500 7.500 Interest crediting rate 5.000 5.000 Postretirement benefits Discount rate 3.550 % 2.750 % Actuarial assumptions used for the CNA Retirement Plan and CNA Health and Group Benefits Program to determine net cost or benefit are presented in the following table. Years ended December 31 2018 2017 2016 Pension benefits Discount rate 3.550 % 3.950 % 4.150 % Expected long term rate of return 7.500 7.500 7.500 Interest crediting rate 5.000 5.000 5.000 Postretirement benefits Discount rate 2.750 % 2.750 % 2.750 % To determine the discount rate assumption as of the year-end measurement date for the CNA Retirement Plan and CNA Health and Group Benefits Program, the Company considered the estimated timing of plan benefit payments and available yields on high quality fixed income debt securities. For this purpose, high quality is considered a rating of Aa or better by Moody's or a rating of AA or better from S&P. The Company reviewed several yield curves constructed using the cash flow characteristics of the plans as well as bond indices as of the measurement date. The trend of those data points was also considered. In determining the expected long term rate of return on plan assets assumption for the CNA Retirement Plan, CNA considered the historical performance of the benefit plan investment portfolio as well as long term market return expectations based on the investment mix of the portfolio and the expected investment horizon. The CNA Health and Group Benefits Program has limited its share of the health care trend rate to a cost-of-living adjustment of 4% per year. For all participants, the employer subsidy on health care costs will not increase by more than 4% per year. As a result, the assumed health care cost trend rate used in measuring the accumulated postretirement benefit obligation for the CNA Health and Group Benefits Program was 4% per year in 2018 , 2017 and 2016 . CNA employs a total return approach whereby a mix of equity, limited partnerships and fixed maturity securities are used to maximize the long term return of retirement plan assets for a prudent level of risk and to manage cash flows according to plan requirements. The target allocation of plan assets is 40% to 60% invested in equity securities and limited partnerships, with the remainder primarily invested in fixed maturity securities. Alternative investments, including limited partnerships, are used to enhance risk adjusted long term returns while improving portfolio diversification. The intent of this strategy is to minimize the Company's expense related to funding the plan by generating investment returns that exceed the growth of the plan liabilities over the long run. Risk tolerance is established after careful consideration of the plan liabilities, plan funded status and corporate financial conditions. As of December 31, 2018 , the Plan had committed approximately $93 million to future capital calls from various third-party limited partnership investments in exchange for an ownership interest in the related partnerships. Derivatives may be used to gain market exposure in an efficient and timely manner. Investment risk is measured and monitored on an ongoing basis through annual liability measurements, periodic asset/liability studies and quarterly investment portfolio reviews. Pension plan assets measured at fair value on a recurring basis as well as cash are presented in the following tables. December 31, 2018 (In millions) Level 1 Level 2 Level 3 Total Assets Fixed maturity securities: Corporate bonds and other $ — $ 472 $ 10 $ 482 States, municipalities and political subdivisions — 58 — 58 Asset-backed — 165 — 165 Total fixed maturity securities — 695 10 705 Equity securities 331 110 — 441 Short term investments 27 54 — 81 Other assets — 9 — 9 Total assets measured at fair value $ 358 $ 868 $ 10 1,236 Total limited partnerships measured at net asset value (1) 789 Total plan assets $ 2,025 December 31, 2017 (In millions) Level 1 Level 2 Level 3 Total Assets Fixed maturity securities: Corporate bonds and other $ — $ 522 $ 10 $ 532 States, municipalities and political subdivisions — 62 — 62 Asset-backed — 180 — 180 Total fixed maturity securities — 764 10 774 Equity securities 405 122 — 527 Short term investments 23 11 — 34 Other assets — 9 — 9 Cash 13 — — 13 Total assets measured at fair value $ 441 $ 906 $ 10 1,357 Total limited partnerships measured at net asset value (1) 904 Total plan assets $ 2,261 (1) Certain investments that are measured at fair value using the net asset value per share (or its equivalent) practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in this table for these investments are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the Plan's Statement of Financial Position. The limited partnership investments held within the plan are recorded at fair value, which represents the plan's share of net asset value of each partnership, as determined by the general partner. Limited partnerships comprising 81% and 85% of the carrying value as of December 31, 2018 and 2017 employ hedge fund strategies that generate returns through investing in marketable securities in the public fixed income and equity markets and the remainder were primarily invested in private debt and equity. Within hedge fund strategies, approximately 66% were equity related, 28% pursued a multi-strategy approach and 6% were focused on distressed investments as of December 31, 2018 . For a discussion of the fair value levels and the valuation methodologies used to measure fixed maturity securities, equities, derivatives and short term investments, see Note C to the Consolidated Financial Statements. The table below presents the estimated future minimum benefit payments to participants as of December 31, 2018 . (In millions) Pension Benefits Postretirement Benefits 2019 $ 175 $ 2 2020 174 2 2021 175 1 2022 177 1 2023 177 1 2024-2028 850 2 In 2019 , CNA expects to contribute $8 million to its pension plans and $2 million to its postretirement health care benefit plans. Savings Plans CNA sponsors savings plans, which are generally contributory plans that allow most employees to contribute a maximum of 50% of their eligible compensation, subject to certain limitations prescribed by the IRS. The Company contributes matching amounts to participants, amounting to 70% of the first 6% ( 35% of the first 6% in the first year of employment) of eligible compensation contributed by the employee. Matching contributions vest ratably over participants first five years of service. Eligible employees also receive a Company contribution of 3% or 5% of their eligible compensation, depending on their age. In addition, these employees are eligible to receive additional discretionary contributions of up to 2% of eligible compensation and an additional Company match of up to 80% of the first 6% of eligible compensation contributed by the employee. These additional contributions are made at the discretion of management and are contributed to participant accounts in the first quarter of the year following management's determination of the discretionary amounts. Matching contributions vest ratably over participants first five years of service. Benefit expense for the Company's savings plans was $71 million , $76 million and $75 million for the years ended December 31, 2018 , 2017 and 2016 .

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-Based Compensation	Stock-Based Compensation The current CNAF Incentive Compensation Plan (the Plan) authorizes the grant of stock-based compensation to certain management personnel for up to 11 million shares of CNAF common stock. The Plan currently provides for awards of stock options, stock appreciation rights (SARs), restricted shares, restricted stock units (RSUs), performance-based RSUs and performance share units. The number of shares available for the granting of stock-based compensation under the Plan as of December 31, 2018 was approximately 1.8 million . The Company recorded stock-based compensation expense related to the Plan of $32 million , $36 million and $36 million for the years ended December 31, 2018 , 2017 and 2016 . The related income tax benefit recognized was $8 million , $18 million and $12 million for the years ended December 31, 2018 , 2017 and 2016 . The compensation cost not yet recognized was $44 million , and the weighted average period over which it is expected to be recognized is 1.7 years as of December 31, 2018 . Equity based compensation that is not fully vested prior to termination is generally forfeited upon termination, except in cases of retirement, death or disability, and as otherwise provided by contractual obligations. Share Awards The fair value of share awards is based on the market value of the Company's common stock as of the date of grant, except for awards made to foreign participants, which is based on the current market value of the Company’s common stock. Generally, RSUs vest over a two or three -year service period following the date of grant. Performance-based RSUs generally become payable within a range of 0% to 100% of the number of shares initially granted based upon the attainment of specific annual performance goals and vest ratably over a four -year service period following the date of grant. As of December 31, 2018 and 2017 , the Company does not have any outstanding performance-based RSUs. In 2016, CNA adopted the Annual Performance Share Plan (PSP). The PSP provides officers with an opportunity to earn an award based upon attainment of specific performance goals achieved over a one -year performance period. Awards are granted at the beginning of each performance year and are generally subject to a two -year cliff vesting period after the Company’s annual performance has been determined. Prior to the PSP, CNA issued performance share units under the Long Term Incentive Plan (LTI Plan). The LTI Plan had a three -year performance period and was settled during 2018. In both plans, the performance share units become payable within a range of 0% to 200% of the number of performance share units initially granted. In 2016, CNA granted Special Supplemental Equity Awards (SSE). The awards consisted of restricted stock units subject to both Company performance in 2016 and service-based vesting up to two years. As of December 31, 2018 , the Company does not have any outstanding SSE restricted stock units. Payments made under the PSP and SSE are made entirely in shares of common stock, except for awards made to foreign participants, which are paid in cash. The total fair value of RSUs and performance shares that vested during the years ended December 31, 2018 , 2017 and 2016 was $16 million , $34 million and $12 million , respectively. The weighted average grant date fair value for RSUs and performance shares granted during the years ended December 31, 2018 , 2017 and 2016 was $51.64 , $44.20 and $32.27 , respectively. The following table presents activity for non-vested RSUs and performance share units under the Plan in 2018 . Number of Awards Weighted-Average Grant Date Fair Value Balance as of January 1, 2018 2,070,737 $ 38.92 Awards granted 840,961 51.64 Awards vested (463,725 ) 38.62 Awards forfeited, canceled or expired (307,719 ) 40.59 Performance-based adjustment 63,894 52.00 Balance as of December 31, 2018 2,204,148 43.98

Other Intangible Assets

Other Intangible Assets	12 Months Ended
	Dec. 31, 2018
Intangible Assets, Gross (Excluding Goodwill) [Abstract]
Other Intangible Assets	Other Intangible Assets Other intangible assets are presented in the following table. December 31 2018 2017 (In millions) Economic Useful Life Carrying Amount Accumulated Amortization Carrying Amount Accumulated Amortization Finite-lived intangible assets: Trade name 8 years $ 6 $ 5 $ 7 $ 5 Distribution channel 15 years 10 4 11 4 Total finite-lived intangible assets 16 9 18 9 Indefinite-lived intangible assets: Syndicate capacity 45 47 Agency force 16 16 Total indefinite-lived intangible assets 61 63 Total other intangible assets $ 77 $ 9 $ 81 $ 9 The Company's other intangible assets primarily relate to the purchase of Hardy, and the amortization of the finite-lived intangible assets is included in the Statement of Operations for the International segment. For the years ended December 31, 2018 , 2017 and 2016 amortization expense of $1 million , $2 million and $1 million was included in Other operating expenses. The gross carrying amounts and accumulated amortization in the table above may change from period to period as a result of foreign currency translation. Estimated future annual amortization expense for other intangible assets is $1 million in years 2019 through 2023.

Operating Leases

Operating Leases	12 Months Ended
	Dec. 31, 2018
Leases, Operating [Abstract]
Operating Leases	Operating Leases The Company occupies office facilities under lease agreements that expire at various dates. In addition, data processing, office and transportation equipment is leased under agreements that expire at various dates. Most leases contain renewal options that provide for rent increases based on prevailing market conditions. Lease expense for the years ended December 31, 2018 , 2017 and 2016 was $62 million , $66 million and $60 million . The table below presents the expected future minimum lease payments to be made under non-cancelable operating leases as of December 31, 2018 . (In millions) Future Minimum Lease Payments 2019 $ 35 2020 39 2021 41 2022 38 2023 32 Thereafter 200 Total $ 385

Stockholders' Equity and Statut

Stockholders' Equity and Statutory Accounting Practices	12 Months Ended
	Dec. 31, 2018
Stockholders' Equity and Statutory Accounting Practices [Abstract]
Stockholders' Equity And Statutory Accounting Practices	Stockholders’ Equity and Statutory Accounting Practices Common Stock Dividends There are no restrictions on the retained earnings or net income of CNAF with regard to payment of dividends to its stockholders. However, given the holding company nature of CNAF, its ability to pay a dividend is significantly dependent on the receipt of dividends from its subsidiaries, particularly CCC, which directly or indirectly owns all significant subsidiaries. See the Statutory Accounting Practices section below for a discussion of the regulatory restrictions on CCC's availability to pay dividends. CNAF's ability to pay dividends may be indirectly limited by the minimum consolidated net worth covenant in the Company's line of credit agreement. See Note H to the Consolidated Financial Statements for further discussion of the Company's debt obligations. Statutory Accounting Practices CNAF’s insurance subsidiaries are domiciled in various jurisdictions. These subsidiaries prepare statutory financial statements in accordance with accounting practices prescribed or permitted by the respective jurisdictions’ insurance regulators. Domestic prescribed statutory accounting practices are set forth in a variety of publications of the National Association of Insurance Commissioners (NAIC) as well as state laws, regulations and general administrative rules. These statutory accounting principles vary in certain respects from GAAP. In converting from statutory accounting principles to GAAP, the more significant adjustments include deferral of policy acquisition costs and the inclusion of net unrealized holding gains or losses in stockholders’ equity relating to certain fixed maturity securities. The Company has a prescribed practice as it relates to the accounting under Statement of Statutory Accounting Principles No. 62R (SSAP No. 62R), Property and Casualty Reinsurance , paragraphs 67 and 68 in conjunction with the 2010 LPT with NICO which is further discussed in Note E to the Consolidated Financial Statements. The prescribed practice allows the Company to aggregate all third party A&EP reinsurance balances administered by NICO in Schedule F and to utilize the LPT as collateral for the underlying third party reinsurance balances for purposes of calculating the statutory reinsurance penalty. This prescribed practice increased statutory capital and surplus by $88 million and $63 million at December 31, 2018 and 2017 . The payment of dividends by CNAF's insurance subsidiaries without prior approval of the insurance department of each subsidiary’s domiciliary jurisdiction is generally limited by formula. Dividends in excess of these amounts are subject to prior approval by the respective insurance regulator. Dividends from CCC are subject to the insurance holding company laws of the State of Illinois, the domiciliary state of CCC. Under these laws, ordinary dividends, or dividends that do not require prior approval by the Illinois Department of Insurance (the Department), are determined based on the greater of the prior year's statutory net income or 10% of statutory surplus as of the end of the prior year, as well as the timing and amount of dividends paid in the preceding twelve months. Additionally, ordinary dividends may only be paid from earned surplus, which is calculated by removing unrealized gains from unassigned surplus. As of December 31, 2018 , CCC is in a positive earned surplus position. The maximum allowable dividend CCC could pay during 2019 that would not be subject to the Department’s prior approval is $1,383 million , less dividends paid during the preceding twelve months measured at that point in time. CCC paid dividends of $1,026 million in 2018 . The actual level of dividends paid in any year is determined after an assessment of available dividend capacity, holding company liquidity and cash needs as well as the impact the dividends will have on the statutory surplus of the applicable insurance company. Combined statutory capital and surplus and statutory net income (loss) for the Combined Continental Casualty Companies are presented in the table below, determined in accordance with accounting practices prescribed or permitted by insurance and/or other regulatory authorities Statutory Capital and Surplus Statutory Net Income (Loss) December 31 Years ended December 31 (In millions) 2018 (1) 2017 2018 (1) 2017 2016 Combined Continental Casualty Companies $ 10,411 $ 10,726 $ 1,405 $ 1,029 $ 1,033 (1) Information derived from the statutory-basis financial statements to be filed with insurance regulators. CNAF’s domestic insurance subsidiaries are subject to risk-based capital (RBC) requirements. RBC is a method developed by the NAIC to determine the minimum amount of statutory capital appropriate for an insurance company to support its overall business operations in consideration of its size and risk profile. The formula for determining the amount of RBC specifies various factors, weighted based on the perceived degree of risk, which are applied to certain financial balances and financial activity. The adequacy of a company's actual capital is evaluated by a comparison to the RBC results, as determined by the formula. Companies below minimum RBC requirements are classified within certain levels, each of which requires specified corrective action. The statutory capital and surplus presented above for CCC was approximately 266% and 264% of company action level RBC as of December 31, 2018 and 2017 . Company action level RBC is the level of RBC which triggers a heightened level of regulatory supervision. The statutory capital and surplus of the Company's foreign insurance subsidiaries, which is not significant to the overall statutory capital and surplus, also met or exceeded their respective regulatory and other capital requirements.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income (Loss) by Component	12 Months Ended
	Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated Other Comprehensive Income (Loss) by Component	Accumulated Other Comprehensive Income (Loss) by Component The tables below display the changes in Accumulated other comprehensive income (loss) by component. (In millions) Net unrealized gains (losses) on investments with OTTI losses Net unrealized gains (losses) on other investments Pension and postretirement benefits Cumulative foreign currency translation adjustment Total Balance as of January 1, 2018, as previously reported $ 25 $ 750 $ (645 ) $ (98 ) $ 32 Cumulative effect adjustment from accounting change for adoption of ASU 2018-02 (1) 5 137 (130 ) — 12 Cumulative effect adjustment from accounting change for adoption of ASU 2016-01 (1) net of tax (expense) benefit of $-, $8, $-, $- and $8 — (28 ) — — (28 ) Balance as of January 1, 2018, as adjusted 30 859 (775 ) (98 ) 16 Other comprehensive income (loss) before reclassifications (7 ) (801 ) (32 ) (82 ) (922 ) Amounts reclassified from accumulated other comprehensive income (loss) net of tax (expense) benefit of $(2), $2, $8, $- and $8 7 (3 ) (32 ) — (28 ) Other comprehensive income (loss) net of tax (expense) benefit of $4, $211, $1, $- and $216 (14 ) (798 ) — (82 ) (894 ) Balance as of December 31, 2018 $ 16 $ 61 $ (775 ) $ (180 ) $ (878 ) (1) See Note A to the Consolidated Financial Statements for additional information. (In millions) Net unrealized gains (losses) on investments with OTTI losses Net unrealized gains (losses) on other investments Pension and postretirement benefits Cumulative foreign currency translation adjustment Total Balance as of January 1, 2017 $ 30 $ 642 $ (647 ) $ (198 ) $ (173 ) Other comprehensive income (loss) before reclassifications (3 ) 190 (25 ) 100 262 Amounts reclassified from accumulated other comprehensive income (loss) net of tax (expense) benefit of $(1), $(38), $15, $- and $(24) 2 82 (27 ) — 57 Other comprehensive income (loss) net of tax (expense) benefit of $2, $(68), $(9), $- and $(75) (5 ) 108 2 100 205 Balance as of December 31, 2017 $ 25 $ 750 $ (645 ) $ (98 ) $ 32 Amounts reclassified from Accumulated other comprehensive income (loss) shown above are reported in Net income (loss) as follows: Component of AOCI Consolidated Statements of Operations Line Item Affected by Reclassifications Net unrealized gains (losses) on investments with OTTI losses Net realized investment gains (losses) Net unrealized gains (losses) on other investments Net realized investment gains (losses) Pension and postretirement benefits Other operating expenses and Insurance claims and policyholders' benefits

Business Segments

Business Segments	12 Months Ended
	Dec. 31, 2018
Segment Reporting [Abstract]
Business Segments	Business Segments The Company's property and casualty commercial insurance operations are managed and reported in three business segments: Specialty, Commercial and International. These three segments are collectively referred to as Property & Casualty Operations. Specialty provides management and professional liability and other coverages through property and casualty products and services using a network of brokers, independent agencies and managing general underwriters. Commercial works with a network of brokers and independent agents to market a broad range of property and casualty insurance products and services to small, middle-market and large businesses. The International segment underwrites property and casualty coverages on a global basis through its U.K.-based insurance company, a branch operation in Canada as well as through its presence at Lloyd’s of London (Hardy). The Company's operations outside of Property & Casualty Operations are managed and reported in two segments: Life & Group and Corporate & Other. Life & Group primarily includes the results of the individual and group long term care businesses that are in run-off. Corporate & Other primarily includes certain corporate expenses, including interest on corporate debt, and the results of certain property and casualty business in run-off, including CNA Re and A&EP. The accounting policies of the segments are the same as those described in Note A to the Consolidated Financial Statements. The Company manages most of its assets on a legal entity basis, while segment operations are generally conducted across legal entities. As such, only Insurance and Reinsurance receivables, Insurance reserves, Deferred acquisition costs, Goodwill and Deferred non-insurance warranty acquisition expense and revenue are readily identifiable for individual segments. Distinct investment portfolios are not maintained for every individual segment; accordingly, allocation of assets to each segment is not performed. Therefore, a significant portion of Net investment income and Realized investment gains or losses are allocated primarily based on each segment's net carried insurance reserves, as adjusted. All significant intersegment income and expense have been eliminated. Income taxes have been allocated on the basis of the taxable income of the segments. Approximately 9.3% , 7.7% and 7.9% of the Company's direct written premiums were derived from outside the United States for the years ended December 31, 2018 , 2017 and 2016 . In the following tables, certain financial measures are presented to provide information used by management to monitor the Company's operating performance. Management utilizes these financial measures to monitor the Company's insurance operations and investment portfolio. The performance of the Company's insurance operations is monitored by management through core income (loss), which is derived from certain income statement amounts. The Company's investment portfolio is monitored by management through analysis of various factors including unrealized gains and losses on securities, portfolio duration and exposure to market and credit risk. Core income (loss) is calculated by excluding from net income (loss) the after-tax effects of i) net realized investment gains (losses), ii) income or loss from discontinued operations, iii) any cumulative effects of changes in accounting guidance and iv) deferred tax asset and liability remeasurement as a result of an enacted U.S. Federal tax rate change. The calculation of core income (loss) excludes net realized investment gains or losses because net realized investment gains or losses are generally driven by economic factors that are not necessarily consistent with key drivers of underwriting performance, and are therefore not considered an indication of trends in insurance operations. The Company's results of operations and selected balance sheet items by segment are presented in the following tables. Year ended December 31, 2018 Specialty Commercial International Life & Group Corporate & Other (In millions) Eliminations Total Net written premiums $ 2,744 $ 3,060 $ 1,018 $ 524 $ — $ (1 ) $ 7,345 Operating revenues Net earned premiums $ 2,732 $ 3,050 $ 1,001 $ 530 $ — $ (1 ) $ 7,312 Net investment income 439 500 57 801 20 — 1,817 Non-insurance warranty revenue 1,007 — — — — — 1,007 Other revenues 2 28 1 2 19 (2 ) 50 Total operating revenues 4,180 3,578 1,059 1,333 39 (3 ) 10,186 Claims, benefits and expenses Net incurred claims and benefits 1,526 2,053 699 1,218 51 — 5,547 Policyholders’ dividends 5 20 — — — — 25 Amortization of deferred acquisition costs 599 505 231 — — — 1,335 Non-insurance warranty expense 923 — — — — — 923 Other insurance related expenses 279 505 135 122 (1 ) (1 ) 1,039 Other expenses 46 43 14 7 193 (2 ) 301 Total claims, benefits and expenses 3,378 3,126 1,079 1,347 243 (3 ) 9,170 Core income (loss) before income tax 802 452 (20 ) (14 ) (204 ) — 1,016 Income tax (expense) benefit on core income (loss) (173 ) (95 ) 1 57 39 — (171 ) Core income (loss) $ 629 $ 357 $ (19 ) $ 43 $ (165 ) $ — 845 Net realized investment gains (losses) (52 ) Income tax (expense) benefit on net realized investment gains (losses) 14 Net realized investment gains (losses), after tax (38 ) Net deferred tax asset remeasurement 6 Net income $ 813 December 31, 2018 (In millions) Reinsurance receivables $ 649 $ 795 $ 250 $ 414 $ 2,347 $ — $ 4,455 Insurance receivables 947 1,277 284 9 (152 ) — 2,365 Deferred acquisition costs 308 230 95 — — — 633 Goodwill 117 — 29 — — — 146 Deferred non-insurance warranty acquisition expense 2,513 — — — — — 2,513 Insurance reserves Claim and claim adjustment expenses 5,465 8,743 1,750 3,601 2,425 — 21,984 Unearned premiums 2,132 1,454 475 122 — — 4,183 Future policy benefits — — — 10,597 — — 10,597 Deferred non-insurance warranty revenue 3,402 — — — — — 3,402 Year ended December 31, 2017 Specialty Commercial International Life & Group Corporate & Other (In millions) Eliminations Total Net written premiums $ 2,731 $ 2,922 $ 881 $ 536 $ — $ (1 ) $ 7,069 Operating revenues Net earned premiums $ 2,712 $ 2,881 $ 857 $ 539 $ — $ (1 ) $ 6,988 Net investment income 522 658 52 782 20 — 2,034 Non-insurance warranty revenue 390 — — — — — 390 Other revenues 1 32 — 2 2 — 37 Total operating revenues 3,625 3,571 909 1,323 22 (1 ) 9,449 Claims, benefits and expenses Net incurred claims and benefits 1,533 1,930 575 1,269 (19 ) — 5,288 Policyholders’ dividends 4 18 — — — — 22 Amortization of deferred acquisition costs 590 481 162 — — — 1,233 Non-insurance warranty expense 299 — — — — — 299 Other insurance related expenses 279 530 162 129 (1 ) (1 ) 1,098 Other expenses 43 57 (7 ) 7 192 — 292 Total claims, benefits and expenses 2,748 3,016 892 1,405 172 (1 ) 8,232 Core income (loss) before income tax 877 555 17 (82 ) (150 ) — 1,217 Income tax (expense) benefit on core income (loss) (295 ) (186 ) (9 ) 132 60 — (298 ) Core income (loss) $ 582 $ 369 $ 8 $ 50 $ (90 ) $ — 919 Net realized investment gains (losses) 93 Income tax (expense) benefit on net realized investment gains (losses) (30 ) Net realized investment gains (losses), after tax 63 Net deferred tax asset remeasurement (83 ) Net income $ 899 December 31, 2017 (In millions) Reinsurance receivables $ 671 $ 654 $ 212 $ 438 $ 2,315 $ — $ 4,290 Insurance receivables 969 1,103 254 8 2 — 2,336 Deferred acquisition costs 318 223 93 — — — 634 Goodwill 117 — 31 — — — 148 Deferred non-insurance warranty acquisition expense 212 — — — — — 212 Insurance reserves Claim and claim adjustment expenses 5,669 8,764 1,636 3,499 2,436 — 22,004 Unearned premiums 2,020 1,409 472 128 — — 4,029 Future policy benefits — — — 11,179 — — 11,179 Deferred non-insurance warranty revenue 972 — — — — — 972 Year ended December 31, 2016 Specialty Commercial Life & Group Corporate & Other (In millions) International Eliminations Total Net written premiums $ 2,738 $ 2,883 $ 821 $ 547 $ — $ (1 ) $ 6,988 Operating revenues Net earned premiums $ 2,743 $ 2,840 $ 806 $ 536 $ — $ (1 ) $ 6,924 Net investment income 497 657 51 767 16 — 1,988 Non-insurance warranty revenue 361 — — — — — 361 Other revenues 1 32 — (2 ) 12 — 43 Total operating revenues 3,602 3,529 857 1,301 28 (1 ) 9,316 Claims, benefits and expenses Net incurred claims and benefits 1,489 1,905 492 1,286 98 — 5,270 Policyholders’ dividends 4 9 — — — — 13 Amortization of deferred acquisition costs 586 475 174 — — — 1,235 Non-insurance warranty expense 271 — — — — — 271 Other insurance related expenses 295 566 133 132 (3 ) (1 ) 1,122 Other expenses 41 36 24 8 209 — 318 Total claims, benefits and expenses 2,686 2,991 823 1,426 304 (1 ) 8,229 Core income (loss) before income tax 916 538 34 (125 ) (276 ) — 1,087 Income tax (expense) benefit on core income (loss) (310 ) (183 ) (13 ) 145 98 — (263 ) Core income (loss) $ 606 $ 355 $ 21 $ 20 $ (178 ) $ — 824 Net realized investment gains (losses) 50 Income tax (expense) benefit on net realized investment gains (losses) (15 ) Net realized investment gains (losses), after tax 35 Net income $ 859 The following table presents operating revenue by line of business for each reportable segment. Years ended December 31 (In millions) 2018 2017 2016 Specialty Management & Professional Liability $ 2,440 $ 2,533 $ 2,562 Surety 571 541 529 Warranty & Alternative Risks (1) 1,169 551 511 Specialty revenues 4,180 3,625 3,602 Commercial Middle Market 2,045 1,965 1,823 Small Business 472 480 582 Other Commercial Insurance 1,061 1,126 1,124 Commercial revenues 3,578 3,571 3,529 International Canada 255 224 203 Europe 363 326 314 Hardy 441 359 340 International revenues 1,059 909 857 Life & Group revenues 1,333 1,323 1,301 Corporate & Other revenues 39 22 28 Eliminations (3 ) (1 ) (1 ) Total operating revenues 10,186 9,449 9,316 Net realized investment gains (losses) (52 ) 93 50 Total revenues $ 10,134 $ 9,542 $ 9,366 (1) As of January 1, 2018, the Company adopted ASU 2014-09 Revenue Recognition (Topic 606): Revenue from Contracts with Customers . See Note A to the Consolidated Financial Statements for additional information.

Quarterly Financial Data (Unaud

Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Data [Abstract]
Quarterly Financial Data (Unaudited)	Quarterly Financial Data (Unaudited) The following tables present unaudited quarterly financial data. 2018 (In millions, except per share data) First Second Third Fourth Full Year Revenues $ 2,535 $ 2,574 $ 2,622 $ 2,403 $ 10,134 Net income (loss) (1) $ 291 $ 270 $ 336 $ (84 ) $ 813 Basic earnings (loss) per share $ 1.07 $ 0.99 $ 1.24 $ (0.31 ) $ 2.99 Diluted earnings (loss) per share $ 1.07 $ 0.99 $ 1.23 $ (0.31 ) $ 2.98 2017 (In millions, except per share data) First Second Third Fourth Full Year Revenues $ 2,330 $ 2,366 $ 2,398 $ 2,448 $ 9,542 Net income (loss) (2)(3) $ 260 $ 272 $ 144 $ 223 $ 899 Basic earnings (loss) per share $ 0.96 $ 1.01 $ 0.53 $ 0.82 $ 3.32 Diluted earnings (loss) per share $ 0.96 $ 1.00 $ 0.53 $ 0.82 $ 3.30 (1) Net income (loss) in the fourth quarter of 2018 included a loss on limited partnership and common stock investments of $109 million and catastrophe losses, net of reinsurance, of $107 million related to Hurricane Michael and the California wildfires. (2) Net income (loss) in the third quarter of 2017 included catastrophe losses, net of reinsurance and including reinstatement premiums, of $188 million related to Hurricanes Harvey, Irma and Maria. (3) Net income (loss) in the fourth quarter of 2017 included a one-time non-cash increase to Income tax expense of $83 million as a result of Tax Reform Legislation.

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2018
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions The Company reimburses Loews for, or pays directly, fees and expenses of investment facilities and services provided to the Company. Additionally, beginning in 2018, the Company provides investment-related processing services to Loews. The net amounts incurred by the Company for these fees, expenses and services were $43 million for each of the years ended December 31, 2018 , 2017 and 2016 . Net amounts due to Loews, included in Other liabilities and payable in the first quarter of the subsequent year, were $23 million and $22 million as of December 31, 2018 and 2017 . In addition, the Company reimbursed Loews for general corporate services and related travel expenses of less than $1 million for the each of the years ended December 31, 2018 and 2017 . The CNA Tax Group is included in the consolidated federal income tax return of Loews and its eligible subsidiaries. The related receivable from Loews, included in Other assets, was $8 million as of December 31, 2018 . The related payable to Loews, included in Other liabilities, was $121 million as of December 31, 2017 . For a detailed description of the income tax agreement with Loews see Note D to the Consolidated Financial Statements. In addition, the Company writes, at standard rates, a limited amount of insurance for Loews and its subsidiaries. The earned premiums for each of the years ended December 31, 2018 , 2017 and 2016 were $2 million .

Non-Insurance Revenues from Con

Non-Insurance Revenues from Contracts with Customers	12 Months Ended
	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
Non-Insurance Revenues from Contracts with Customers	Non-Insurance Revenues from Contracts with Customers Non-Insurance revenue is recognized when obligations under the terms of a contract with a customer are satisfied; generally this occurs over time as obligations are fulfilled. Revenue is measured as the amount of consideration the Company expects to receive in exchange for providing services. Deferred Non-Insurance Warranty Revenue The Company had deferred non-insurance warranty revenue balances of $2.9 billion and $3.4 billion reported in Deferred non-insurance warranty revenue as of January 1, 2018 and December 31, 2018 . The increase in the deferred revenue balance for the year ended December 31, 2018 was primarily driven by deferrals outpacing revenue recognized in the period due to growth in the business. For the year ended December 31, 2018 , the Company recognized $834 million of revenues that were included in the deferred revenue balance as of January 1, 2018 . For the year ended December 31, 2018 , Non-insurance warranty revenue recognized from performance obligations related to prior periods due to a change in estimate was not material. The Company expects to recognize approximately $963 million of the deferred revenue in 2019, $791 million in 2020, $613 million in 2021 and $1.0 billion thereafter. Cost to Obtain and Fulfill Non-Insurance Warranty Contracts with Customers As of December 31, 2018 , capitalized commission costs were $2.5 billion and capitalized administrator service costs were $24 million . For the year ended December 31, 2018 , the amount of amortization of capitalized costs was $673 million and there was no impairment loss related to the costs capitalized. There were no adjustments to deferred costs recorded for the year ended December 31, 2018 .

Schedule I. Summary of Investme

Schedule I. Summary of Investments - Other Than Investments in Related Parties	12 Months Ended
	Dec. 31, 2018
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Abstract]
Schedule I. Summary of Investments - Other than Investments in Related Parties	SCHEDULE I. SUMMARY OF INVESTMENTS - OTHER THAN INVESTMENTS IN RELATED PARTIES Incorporated herein by reference to Note B to the Consolidated Financial Statements included under Item 8.

Schedule II. Condensed Financia

Schedule II. Condensed Financial Information of Registrant (Parent Company)	12 Months Ended
	Dec. 31, 2018
Condensed Financial Information Disclosure [Abstract]
Schedule II. Condensed Financial Information of Registrant (Parent Company)	SCHEDULE II. CONDENSED FINANCIAL INFORMATION OF REGISTRANT (PARENT COMPANY) CNA Financial Corporation Statements of Operations and Comprehensive (Loss) Income Years ended December 31 (In millions) 2018 2017 2016 Revenues Net investment income $ 10 $ 6 $ 3 Net realized investment (losses) gains — (42 ) (7 ) Total revenues 10 (36 ) (4 ) Expenses Administrative and general 1 2 1 Interest 135 152 155 Total expenses 136 154 156 Loss from operations before income taxes and equity in net income of subsidiaries (126 ) (190 ) (160 ) Income tax benefit 9 57 41 Loss before equity in net income of subsidiaries (117 ) (133 ) (119 ) Equity in net income of subsidiaries 930 1,032 978 Net income 813 899 859 Equity in other comprehensive income of subsidiaries (894 ) 205 142 Total comprehensive (loss) income $ (81 ) $ 1,104 $ 1,001 See accompanying Notes to Condensed Financial Information as well as the Consolidated Financial Statements and accompanying Notes. CNA Financial Corporation Balance Sheets December 31 (In millions, except share data) 2018 2017 Assets Investment in subsidiaries $ 13,427 $ 14,481 Cash 1 1 Short term investments 519 638 Amounts due from affiliates 2 4 Other assets — 1 Total assets $ 13,949 $ 15,125 Liabilities Short term debt $ — $ 150 Long term debt 2,680 2,678 Other liabilities 52 53 Total liabilities 2,732 2,881 Stockholders' Equity Common stock ($2.50 par value; 500,000,000 shares authorized; 273,040,243 shares issued; 271,456,978 and 271,205,390 shares outstanding) 683 683 Additional paid-in capital 2,192 2,175 Retained earnings 9,277 9,414 Accumulated other comprehensive income (878 ) 32 Treasury stock (1,583,265 and 1,834,853 shares), at cost (57 ) (60 ) Total stockholders' equity 11,217 12,244 Total liabilities and stockholders' equity $ 13,949 $ 15,125 See accompanying Notes to Condensed Financial Information as well as the Consolidated Financial Statements and accompanying Notes. CNA Financial Corporation Statements of Cash Flows Years ended December 31 (In millions) 2018 2017 2016 Cash Flows from Operating Activities Net income $ 813 $ 899 $ 859 Adjustments to reconcile net income to net cash flows provided by operating activities: Equity in net income of subsidiaries (930 ) (1,032 ) (978 ) Dividends received from subsidiaries 1,026 955 765 Net realized investment losses — 42 7 Other, net 16 36 21 Total adjustments 112 1 (185 ) Net cash flows provided by operating activities 925 900 674 Cash Flows from Investing Activities Change in short term investments 130 (146 ) (9 ) Capital contributions to subsidiaries (2 ) — — Other, net — — 4 Net cash flows provided (used) by investing activities 128 (146 ) (5 ) Cash Flows from Financing Activities Dividends paid to common stockholders (896 ) (842 ) (813 ) Proceeds from the issuance of debt — 496 498 Repayment of debt (150 ) (391 ) (358 ) Other, net (7 ) (17 ) 1 Net cash flows used by financing activities (1,053 ) (754 ) (672 ) Net change in cash — — (3 ) Cash, beginning of year 1 1 4 Cash, end of year $ 1 $ 1 $ 1 See accompanying Notes to Condensed Financial Information as well as the Consolidated Financial Statements and accompanying Notes. Notes to Condensed Financial Information A. Summary of Significant Accounting Policies Basis of Presentation The condensed financial information of CNA Financial Corporation (CNAF or the Parent Company) should be read in conjunction with the Consolidated Financial Statements and Notes thereto included in Item 8 of this Form 10-K. CNAF’s subsidiaries are accounted for using the equity method of accounting. Equity in net income of these subsidiaries is presented on the Condensed Statements of Operations as Equity in net income of subsidiaries. Loews owned approximately 89% of the outstanding common stock of CNAF as of December 31, 2018 . B. Guarantees As of December 31, 2018 and 2017 CNAF had recorded liabilities of approximately $5 million related to guarantee agreements. The Parent Company believes that it is not likely that any future indemnity claims will be significantly greater than the amounts recorded. In the course of selling business entities and assets to third parties, CNAF has agreed to guarantee the performance of certain obligations of both a previously owned subsidiary and a current subsidiary. Such obligations include agreement to indemnify purchasers for losses arising out of breaches of representation and warranties with respect to the business entities or assets sold, including, in certain cases, losses arising from undisclosed liabilities or certain named litigation. The guarantee agreements may include provisions that survive indefinitely. As of December 31, 2018 , the aggregate amount of quantifiable guarantee agreements in effect for sales of business entities, assets and third-party loans was $625 million . Should the company be required to make payments under the guarantee, it would have the right to seek reimbursement in certain cases from an affiliate of a previously owned subsidiary. In addition, CNAF has agreed to provide indemnification to third-party purchasers for certain losses associated with sold business entities or assets that are not limited by a contractual monetary amount. As of December 31, 2018 , CNAF had outstanding unlimited indemnifications in connection with the sales of certain of its business entities or assets that included tax liabilities arising prior to a purchaser’s ownership of an entity or asset, defects in title at the time of sale, employee claims arising prior to closing and in some cases losses arising from certain litigation and undisclosed liabilities. These indemnification agreements survive until the applicable statutes of limitation expire or until the agreed upon contract terms expire. CNAF also provided guarantees, if the primary obligor fails to perform, to holders of structured settlement annuities provided by a previously owned subsidiary. As of December 31, 2018 , the potential amount of future payments CNAF could be required to pay under these guarantees was approximately $1.8 billion , which will be paid over the lifetime of the annuitants. The Parent Company does not believe a payable is likely under these guarantees, as it is the beneficiary of a trust that must be maintained at a level that approximates the discounted reserves for these annuities.

Schedule III. Supplementary Ins

Schedule III. Supplementary Insurance Information	12 Months Ended
	Dec. 31, 2018
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Abstract]
Schedule III. Supplementary Insurance Information	SCHEDULE III. SUPPLEMENTARY INSURANCE INFORMATION Incorporated herein by reference to Note O to the Consolidated Financial Statements included under Item 8.

Schedule IV. Reinsurance

Schedule IV. Reinsurance	12 Months Ended
	Dec. 31, 2018
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Abstract]
Schedule IV. Reinsurance	SCHEDULE IV. REINSURANCE Incorporated herein by reference to Note G to the Consolidated Financial Statements included under Item 8.

Schedule V. Valuation and Quali

Schedule V. Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2018
SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]
Schedule V. Valuation and Qualifying Accounts	SCHEDULE V. VALUATION AND QUALIFYING ACCOUNTS (In millions) Balance at Beginning of Period Charged to Costs and Expenses Charged to Other Accounts (1) Deductions Balance at End of Period Year ended December 31, 2018 Deducted from assets: Allowance for doubtful accounts: Insurance and reinsurance receivables $ 73 $ 4 $ — $ (6 ) $ 71 Year ended December 31, 2017 Deducted from assets: Allowance for doubtful accounts: Insurance and reinsurance receivables $ 83 $ (1 ) $ — $ (9 ) $ 73 Year ended December 31, 2016 Deducted from assets: Allowance for doubtful accounts: Insurance and reinsurance receivables $ 89 $ (2 ) $ (1 ) $ (3 ) $ 83 (1) Amount includes effects of foreign currency translation.

Schedule VI. Supplemental Infor

Schedule VI. Supplemental Information Concerning Property and Casualty Insurance Operations	12 Months Ended
	Dec. 31, 2018
SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters [Abstract]
Schedule VI. Supplemental Information Concerning Property and Casualty Insurance Operations	SCHEDULE VI. SUPPLEMENTAL INFORMATION CONCERNING PROPERTY AND CASUALTY INSURANCE OPERATIONS As of and for the years ended December 31 Consolidated Property and Casualty Operations (In millions) 2018 2017 2016 Balance Sheet Data Deferred acquisition costs $ 632 $ 632 Reserves for unpaid claim and claim adjustment expenses 21,984 22,004 Discount deducted from claim and claim adjustment expense reserves above (based on interest rates ranging from 3.5% to 8.0%) 1,388 1,434 Unearned premiums 4,183 4,029 Statement of Operations Data Net written premiums $ 7,345 $ 7,069 $ 6,988 Net earned premiums 7,312 6,988 6,924 Net investment income 1,751 1,992 1,952 Incurred claim and claim adjustment expenses related to current year 5,358 5,201 5,025 Incurred claim and claim adjustment expenses related to prior years (179 ) (381 ) (342 ) Amortization of deferred acquisition costs 1,335 1,233 1,235 Paid claim and claim adjustment expenses 5,331 5,341 5,134

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Consolidation	The Consolidated Financial Statements include the accounts of CNA Financial Corporation (CNAF) and its subsidiaries. Collectively, CNAF and its subsidiaries are referred to as CNA or the Company. Loews Corporation (Loews) owned approximately 89% of the outstanding common stock of CNAF as of December 31, 2018 . The accompanying Consolidated Financial Statements have been prepared in conformity with GAAP. Intercompany amounts have been eliminated.
Use of Estimates	The preparation of Consolidated Financial Statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the Consolidated Financial Statements and the reported amounts of revenues and expenses during the reporting period. Actual results may differ from those estimates.
Recently Adopted Accounting Standards Updates and Accounting Standards Pending Adoption	Recently Adopted Accounting Standards Updates (ASU) ASU 2014-09: In May 2014, the FASB issued ASU No. 2014-09, Revenue Recognition (Topic 606) : Revenue from Contracts with Customers . The standard excludes from its scope the accounting for insurance contracts, financial instruments, and certain other agreements that are governed under other GAAP guidance, but the standard does apply to certain of the Company's warranty products and services. The updated guidance requires an entity to recognize revenue as performance obligations are met, in an amount that reflects the consideration the entity is entitled to receive for the transfer of the promised goods or services. On January 1, 2018, the Company adopted the updated guidance using the modified retrospective method applied to all contracts which were not completed as of the date of adoption, with the cumulative effect recognized as an adjustment to the opening balance of Retained earnings. Prior period amounts have not been adjusted and continue to be reported in accordance with the previous accounting guidance. Under the new guidance, revenue on warranty products and services is recognized more slowly as compared to the historic revenue recognition pattern. In addition, for warranty products where the Company acts as the principal in the transaction, Non-insurance warranty revenue and Non-insurance warranty expense are increased to reflect the gross amount paid by consumers, including the retail seller’s markup which is considered a commission to the Company's agent. This gross-up of revenue and expense also resulted in an increase to Deferred non-insurance warranty acquisition expense and Deferred non-insurance warranty revenue on the Company's Consolidated Balance Sheets as the revenue and expense are recognized over the actuarially determined expected claims emergence pattern. The cumulative effect changes to the Consolidated Balance Sheet for the adoption of the updated guidance on January 1, 2018 were as follows: (In millions) Balance as of December 31, 2017 Adjustments Due to Adoption of Topic 606 Balance as of January 1, 2018 Deferred non-insurance warranty acquisition expense $ 212 $ 1,882 $ 2,094 Deferred non-insurance warranty revenue 972 1,969 2,941 Deferred income taxes 137 21 158 Retained earnings 9,414 (66 ) 9,348 The impact of adoption on the Consolidated Statements of Operations and Balance Sheet was as follows: Year ended December 31, 2018 Prior to Adoption Effect of Adoption As Reported (In millions) Statement of operations: Non-insurance warranty revenue $ 420 $ 587 $ 1,007 Total revenues 9,547 587 10,134 Non-insurance warranty expense 328 595 923 Total claims, benefits and expenses 8,575 595 9,170 Income before income tax 972 (8 ) 964 Income tax expense (153 ) 2 (151 ) Net income 819 (6 ) 813 Balance sheet (1) at December 31, 2018: Deferred non-insurance warranty acquisition expense $ 2,116 $ 397 $ 2,513 Deferred non-insurance warranty revenue 2,997 405 3,402 Deferred income taxes 390 2 392 Retained earnings 9,283 (6 ) 9,277 (1) The Prior to Adoption amounts presented in this table include the cumulative effect adjustment at adoption presented in the prior table. See Note R to the Consolidated Financial Statements for additional information regarding non-insurance revenues from contracts with customers. ASU 2016-01: In January 2016, the FASB issued ASU No. 2016-01, Financial Instruments - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities . The updated accounting guidance requires changes to the reporting model for financial instruments. The guidance primarily changes the model for equity securities by requiring changes in the fair value of equity securities (except those accounted for under the equity method of accounting, those without readily determinable fair values and those that result in consolidation of the investee) to be recognized through the income statement. The Company adopted the updated guidance on January 1, 2018 and recognized a cumulative effect adjustment that increased beginning Retained earnings by $28 million , net of tax. Prior period amounts have not been adjusted and continue to be reported in accordance with the previous accounting guidance. For the year ended December 31, 2018 , the Company recognized $74 million in pretax losses within Net realized investment gains (losses) for the change in fair value of non-redeemable preferred stock and $22 million in pretax losses within Net investment income for the change in fair value of common stock as a result of this change. For the year ended December 31, 2017 , there was a $32 million increase in the fair value of non-redeemable preferred stock and a less than $1 million increase in the fair value of common stock, both recognized in Other comprehensive income. For the year ended December 31, 2016 , there was a $6 million decrease in the fair value of non-redeemable preferred stock and a $4 million increase in the fair value of common stock, both recognized in Other comprehensive income. ASU 2017-07: In March 2017, the FASB issued ASU No. 2017-07, Compensation-Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost . The updated accounting guidance requires changes to the presentation of the components of net periodic benefit cost on the income statement by requiring service cost to be presented with other employee compensation costs and other components of net periodic pension cost to be presented outside of any subtotal of operating income. The ASU also stipulates that only the service cost component of net benefit cost is eligible for capitalization. The Company adopted the updated guidance effective January 1, 2018. The guidance was applied on a prospective basis for capitalization of service costs and on a retrospective basis for the presentation of the service cost and other components of net periodic benefit costs in the Company's Consolidated Statements of Operations and in its disclosures. The Company utilized the practical expedient allowing amounts previously disclosed in its Benefit Plans footnote to be used as the estimation basis for prior comparative periods. The Company expanded the related footnote disclosure, Note I to the Consolidated Financial Statements, to disclose the amount of service cost and non-service cost components of net periodic benefit cost and the line items in the Consolidated Statements of Operations in which such amounts are reported. The change limiting the costs eligible for capitalization is not material to the Company’s results of operations or financial position. ASU 2018-02: In February 2018, the FASB issued ASU No. 2018-02, Income Statement - Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income. GAAP requires the remeasurement of deferred tax assets and liabilities due to a change in the tax rate to be included in Net income, even if the related income tax effects were originally recognized in Accumulated other comprehensive income (AOCI). The ASU allows a reclassification from AOCI to Retained earnings for stranded tax effects resulting from the new U.S. Federal corporate income tax rate enacted on December 22, 2017. The Company early adopted the updated guidance effective January 1, 2018 and elected to reclassify the stranded income tax effects relating to the reduction in the Federal corporate income tax rate from AOCI to Retained earnings at the beginning of the period of adoption. The net impact of the accounting change resulted in a $12 million increase in AOCI and a corresponding decrease in Retained earnings. The $12 million increase in AOCI is comprised of a $142 million increase in net unrealized gains (losses) on investments partially offset by a $130 million decrease in unrecognized pension and postretirement benefits. The Company releases tax effects from AOCI utilizing the security-by-security approach for Net unrealized gains (losses) on investments with Other-than-temporary impairment (OTTI) losses and Net unrealized gains (losses) on other investments. For Pension and postretirement benefits, tax effects from AOCI are released at enacted tax rates based on the pre-tax adjustments to pension liabilities or assets recognized within OCI. ASU 2018-13: In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820) Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement. The updated accounting guidance requires changes to the disclosures for fair value measurement by adding, removing and modifying disclosures. This guidance is effective for fiscal years beginning after December 15, 2019, including interim periods therein and early adoption is permitted. As of September 30, 2018, the Company adopted the updated guidance and added disclosures on changes in unrealized gains (losses) on Level 3 assets recognized in Other comprehensive income as well as the weighted average rate used to develop significant inputs utilized in the fair value measurements of Level 3 assets. The Company also eliminated disclosures on the amount of transfers between Level 1 and Level 2 assets and the policy for timing of transfers between Levels. ASU 2018-14: In August 2018, the FASB issued ASU No. 2018-14, Compensation -Retirement Benefits - Defined Benefit Plans - General (Subtopic 715-20) Disclosure Framework - Changes to the Disclosure Requirements for Defined Benefit Plans. The updated accounting guidance modifies the disclosure requirements for employers that sponsor defined benefit pension or other postretirement plans by removing, modifying and adding disclosures. The guidance is effective for annual periods ending after December 15, 2020, and early adoption is permitted. As of December 31, 2018, the Company adopted the updated accounting guidance by eliminating disclosures of the amounts in AOCI expected to be recognized as part of net periodic cost (benefit) during 2019. The Company also added disclosure of the interest crediting rate used in our defined benefit pension plan and a description of significant gains and losses affecting the benefit obligations for the periods presented. Accounting Standards Pending Adoption In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842): Accounting for Leases. The updated accounting guidance requires lessees to recognize on the balance sheet assets and liabilities for the rights and obligations created by the majority of leases, including those historically accounted for as operating leases. The guidance is effective for interim and annual periods beginning after December 15, 2018 and prescribes a modified retrospective transition method but allows entities to utilize a practical expedient and apply the guidance prospectively beginning with the adoption date. The Company has decided to utilize the practical expedient. The Company is finalizing its determination of the effect the updated guidance will have on its financial statements, but currently anticipates that asset and liabilities will increase approximately $230 million at the adoption date. The Company does not expect the impact of adoption to be material to the Company's results of operations. In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. The updated accounting guidance requires changes to the recognition of credit losses on financial instruments not accounted for at fair value through net income. The guidance is effective for interim and annual periods beginning after December 15, 2019. The guidance will be applied using a modified retrospective approach with the cumulative effect recognized as an adjustment to retained earnings. A prospective transition approach is required for debt securities that have recognized an other-than-temporary impairment prior to the effective date. The Company is currently evaluating the effect the guidance will have on the Company's financial statements, but expects the primary changes to be the use of the expected credit loss model for its mortgage loan portfolio, reinsurance and insurance receivables and other financing receivables and the use of the allowance method rather than the write-down method for credit losses within the available-for-sale fixed maturities portfolio. The expected credit loss model will require a financial asset to be presented at the net amount expected to be collected. The allowance method for available-for-sale debt securities will allow the Company to record reversals of credit losses if the estimate of credit losses declines. In August 2018, the FASB issued ASU 2018-12, Financial Services-Insurance (Topic 944): Targeted Improvements to the Accounting for Long-Duration Contracts . The updated accounting guidance requires changes to the measurement and disclosure of long-duration contracts. The guidance requires entities to annually update cash flow assumptions, including morbidity and persistency, and update discount rate assumptions quarterly using an upper-medium grade fixed-income instrument yield. The effect of changes in cash flow assumptions will be recorded in Net income and the effect of changes in discount rate assumptions will be recorded in Other comprehensive income. This guidance is effective for interim and annual periods beginning after December 15, 2020, and requires restatement of the prior periods presented. Early adoption is permitted. The Company is currently evaluating the method and timing of adoption and the effect the updated guidance will have on its financial statements. The annual updating of cash flow assumptions is expected to increase income statement volatility. The quarterly change in discount rate is expected to increase volatility in the Company’s stockholders' equity, but that will be somewhat mitigated because Shadow Adjustments are eliminated under the new guidance
Premiums	Premiums: Insurance premiums on property and casualty insurance contracts are recognized in proportion to the underlying risk insured and are principally earned ratably over the term of the policies. Premiums on long term care contracts are earned ratably over the policy year in which they are due. The reserve for unearned premiums represents the portion of premiums written relating to the unexpired terms of coverage. Insurance receivables include balances due currently or in the future, including amounts due from insureds related to losses under high deductible policies, and are presented at unpaid balances, net of an allowance for uncollectible receivables. Amounts are considered past due based on policy payment terms. The allowance is determined based on periodic evaluations of aged receivables, historical business default data, management's experience and current economic conditions. Insurance receivables and any related allowance are written off after collection efforts are exhausted or a negotiated settlement is reached. Property and casualty contracts that are retrospectively rated contain provisions that result in an adjustment to the initial policy premium depending on the contract provisions and loss experience of the insured during the experience period. For such contracts, the Company estimates the amount of ultimate premiums that the Company may earn upon completion of the experience period and recognizes either an asset or a liability for the difference between the initial policy premium and the estimated ultimate premium. The Company adjusts such estimated ultimate premium amounts during the course of the experience period based on actual results to date. The resulting adjustment is recorded as either a reduction of or an increase to the earned premiums for the period.
Claim and claim adjustment expense reserves	Claim and claim adjustment expense reserves: Claim and claim adjustment expense reserves, except reserves for structured settlements not associated with A&EP, workers' compensation lifetime claims and long term care claims, are not discounted and are based on i) case basis estimates for losses reported on direct business, adjusted in the aggregate for ultimate loss expectations; ii) estimates of incurred but not reported (IBNR) losses; iii) estimates of losses on assumed reinsurance; iv) estimates of future expenses to be incurred in the settlement of claims; v) estimates of salvage and subrogation recoveries and vi) estimates of amounts due from insureds related to losses under high deductible policies. Management considers current conditions and trends as well as past Company and industry experience in establishing these estimates. The effects of inflation, which can be significant, are implicitly considered in the reserving process and are part of the recorded reserve balance. Ceded claim and claim adjustment expense reserves are reported as a component of Reinsurance receivables on the Consolidated Balance Sheets. Claim and claim adjustment expense reserves are presented net of anticipated amounts due from insureds related to losses under deductible policies of $1.2 billion as of December 31, 2018 and 2017 . A significant portion of these amounts are supported by collateral. The Company has an allowance for uncollectible deductible amounts, which is presented as a component of the allowance for doubtful accounts included in Insurance receivables on the Consolidated Balance Sheets. Structured settlements have been negotiated for certain property and casualty insurance claims. Structured settlements are agreements to provide fixed periodic payments to claimants. The Company's obligations for structured settlements not funded by annuities are included in claim and claim adjustment expense reserves and carried at present values determined using interest rates ranging from to 5.5% to 8.0% as of December 31, 2018 and 2017 . As of December 31, 2018 and 2017 , the discounted reserves for unfunded structured settlements were $512 million and $527 million , net of discount of $760 million and $798 million . For the years ended December 31, 2018 , 2017 and 2016 , the amount of interest recognized on the discounted reserves of unfunded structured settlements was $40 million , $41 million and $42 million , respectively. This interest accretion is presented as a component of Insurance claims and policyholders’ benefits on the Consolidated Statements of Operations, but is excluded from the Company’s disclosure of prior year loss reserve development. Workers' compensation lifetime claim reserves are calculated using mortality assumptions determined through statutory regulation and economic factors. At December 31, 2018 and 2017 , workers' compensation lifetime claim reserves are discounted at a 3.5% interest rate. As of December 31, 2018 and 2017 , the discounted reserves for workers’ compensation lifetime claim reserves were $343 million and $346 million , net of discount of $168 million and $190 million . For the years ended December 31, 2018 , 2017 and 2016 , the amount of interest accretion recognized on the discounted reserves of workers’ compensation lifetime claim reserves was $16 million , $19 million and $17 million , respectively. This interest accretion is presented as a component of Insurance claims and policyholders' benefits on the Consolidated Statements of Operations, but is excluded from the Company's disclosure of prior year loss reserve development. Long term care claim reserves are calculated using mortality and morbidity assumptions based on Company and industry experience. Long term care claim reserves are discounted at an interest rate of 6.0% as of December 31, 2018 and 2017 .
Future policy benefits reserves	Future policy benefit reserves: Future policy benefit reserves represent the active life reserves related to the Company's long term care policies and are computed using the net level premium method, which incorporates actuarial assumptions as to morbidity, persistency, inclusive of mortality, discount rate, future premium rate adjustments and expenses. Expense assumptions primarily relate to claim adjudication. The Company's future policy benefit reserves are based on best estimate actuarial assumptions as of the most recent date of loss recognition, which occurred in 2015. If a premium deficiency were to emerge in the future, the assumptions would be unlocked, and the future policy benefit reserves would be adjusted. The GPV process was performed in the third quarter of 2018 as compared to the fourth quarter in 2017. The GPV as of September 30, 2018 and December 31, 2017 indicated the carried reserves were sufficient; therefore, there was no unlocking of assumptions. Interest rates for long term care active life reserves range from 6.6% to 7.0% as of September 30, 2018 and December 31, 2017 . The Company's most recent GPV indicated the future policy benefit reserves for the long term care business were not deficient in the aggregate, but profits are expected to be recognized in early years followed by losses in later years. In that circumstance, future policy benefit reserves are increased in the profitable years by an amount necessary to offset losses that are projected to be recognized in later years. The amount of the additional future policy benefit reserves recorded in each quarterly period is determined by applying the ratio of the present value of future losses divided by the present value of future profits from the most recently completed GPV to long term care core income in that period.
Guaranty fund and other insurance-related assessments	Guaranty fund and other insurance-related assessments: Liabilities for guaranty fund and other insurance-related assessments are accrued when an assessment is probable, when it can be reasonably estimated and when the event obligating the entity to pay an imposed or probable assessment has occurred. Liabilities for guaranty funds and other insurance-related assessments are not discounted and are included as part of Other liabilities on the Consolidated Balance Sheets.
Reinsurance	Reinsurance: Reinsurance accounting allows for contractual cash flows to be reflected as premiums and losses. To qualify for reinsurance accounting, reinsurance agreements must include risk transfer. To meet risk transfer requirements, a reinsurance contract must include both insurance risk, consisting of underwriting and timing risk, and a reasonable possibility of a significant loss for the assuming entity. Reinsurance receivables related to paid losses are presented at unpaid balances. Reinsurance receivables related to unpaid losses are estimated in a manner consistent with claim and claim adjustment expense reserves or future policy benefit reserves. Reinsurance receivables are reported net of an allowance for uncollectible amounts on the Consolidated Balance Sheets. The cost of reinsurance is primarily accounted for over the life of the underlying reinsured policies using assumptions consistent with those used to account for the underlying policies or over the reinsurance contract period. The ceding of insurance does not discharge the primary liability of the Company. The Company has established an allowance for uncollectible reinsurance receivables which relates to both amounts already billed on ceded paid losses as well as ceded reserves that will be billed when losses are paid in the future. The allowance for uncollectible reinsurance receivables is estimated on the basis of periodic evaluations of balances due from reinsurers, reinsurer solvency, industry experience and current economic conditions. Reinsurer financial strength ratings are updated and reviewed on an annual basis or sooner if the Company becomes aware of significant changes related to a reinsurer. Because billed receivables generally approximate 5% or less of total reinsurance receivables, the age of the reinsurance receivables related to paid losses is not a significant input into the allowance analysis. Changes in the allowance for uncollectible reinsurance receivables are presented as a component of Insurance claims and policyholders' benefits on the Consolidated Statements of Operations. Amounts are considered past due based on the reinsurance contract terms. Reinsurance receivables related to paid losses and any related allowance are written off after collection efforts have been exhausted or a negotiated settlement is reached with the reinsurer. Reinsurance receivables from insolvent insurers related to paid losses are written off when the settlement due from the estate can be reasonably estimated. At the time reinsurance receivables related to paid losses are written off, any required adjustment to reinsurance receivables related to unpaid losses is recorded as a component of Insurance claims and policyholders' benefits on the Consolidated Statements of Operations. Reinsurance contracts that do not effectively transfer the economic risk of loss on the underlying policies are recorded using the deposit method of accounting, which requires that premium paid or received by the ceding company or assuming company be accounted for as a deposit asset or liability. The Company had $3 million and $8 million recorded as deposit assets as of December 31, 2018 and 2017 , and $3 million and $4 million recorded as deposit liabilities as of December 31, 2018 and 2017 . Income on reinsurance contracts accounted for under the deposit method is recognized using an effective yield based on the anticipated timing of payments and the remaining life of the contract. When the anticipated timing of payments changes, the effective yield is recalculated to reflect actual payments to date and the estimated timing of future payments. The deposit asset or liability is adjusted to the amount that would have existed had the new effective yield been applied since the inception of the contract. A loss portfolio transfer is a retroactive reinsurance contract. If the cumulative claim and allocated claim adjustment expenses ceded under a loss portfolio transfer exceed the consideration paid, the resulting gain from such excess is deferred and amortized into earnings in future periods in proportion to actual recoveries under the loss portfolio transfer. In any period in which there is a revised estimate of claim and allocated claim adjustment expenses and the loss portfolio transfer is in a gain position, the deferred gain is recalculated as if the revised estimate was available at the inception date of the loss portfolio transfer and the change in the deferred gain is recognized in earnings.
Deferred acquisition costs	Deferred acquisition costs: Deferrable acquisition costs include commissions, premium taxes and certain underwriting and policy issuance costs which are incremental direct costs of successful contract acquisitions. Acquisition costs related to property and casualty business are deferred and amortized ratably over the period the related premiums are earned. Deferred acquisition costs are presented net of ceding commissions and other ceded acquisition costs. The Company evaluates deferred acquisition costs for recoverability. Anticipated investment income is considered in the determination of the recoverability of deferred acquisition costs. Adjustments, if necessary, are recorded in current period results of operations.
Investments in life settlement contracts and related revenue recognition	Investments in life settlement contracts and related revenue recognition: The Company formerly held investments in life settlement contracts. The entire portfolio of life settlement contracts was determined to be held for sale as of December 31, 2016. The Company reached an agreement on terms to sell the portfolio and adjusted the fair value to the estimated sales proceeds less cost to sell. This resulted in a $10 million loss recognized within Net realized investment gains for the year ended December 31, 2016. The sale was completed during 2017 and the Company recorded the consideration, including a note receivable, which is payable over three years and is carried at amortized cost less any valuation allowance. The note receivable was $35 million and $46 million as of December 31, 2018 and 2017 and is included within Other assets on the Consolidated Balance Sheets. Interest income is accreted to the principal balance of the note. The cash receipts and payments related to the life settlement contracts prior to the sale date are included in Cash Flows from operating activities on the Consolidated Statements of Cash Flows. Cash receipts related to the sale of the life settlement contracts, as well as principal payments on the note receivable, are included in Cash Flows from investing activities.
Investments	Investments The Company classifies its fixed maturity securities as either available-for-sale or trading, and as such, they are carried at fair value. Changes in fair value of trading securities are reported within Net investment income on the Consolidated Statements of Operations. Changes in fair value related to available-for-sale securities are reported as a component of Other comprehensive income. Losses may be recognized within Net realized investment gains (losses) on the Consolidated Statements of Operations when a decline in value is determined by the Company to be other-than-temporary. The cost of fixed maturity securities classified as available-for-sale is adjusted for amortization of premiums and accretion of discounts, which are included in Net investment income on the Consolidated Statements of Operations. The amortization of premium and accretion of discount for fixed maturity securities takes into consideration call and maturity dates that produce the lowest yield. For asset-backed securities included in fixed maturity securities, the Company recognizes income using an effective yield based on anticipated prepayments and the estimated economic life of the securities. When estimates of prepayments change, the effective yield is recalculated to reflect actual payments to date and anticipated future payments. To the extent that unrealized gains on fixed maturity securities supporting long term care products and structured settlements not funded by annuities would result in a premium deficiency if those gains were realized, a related increase in Insurance reserves is recorded, net of tax, as a reduction of net unrealized gains through Other comprehensive income (Shadow Adjustments). Shadow Adjustments, net of tax, decreased $333 million and increased $397 million for the years ended December 31, 2018 and 2017 , respectively. As of December 31, 2018 and 2017 , net unrealized gains on investments included in Accumulated other comprehensive income (AOCI) were correspondingly reduced by Shadow Adjustments of $1,078 million and $1,411 million . Equity securities are carried at fair value. The Company's non-redeemable preferred stock contain characteristics of debt securities, are priced similarly to bonds and are held primarily for income generation through periodic dividends. While recognition of gains and losses on these securities is not discretionary, management does not consider the changes in fair value of non-redeemable preferred stock to be reflective of our primary operations. As such, the changes in the fair value of these securities are recorded through Net realized investments gains (losses). The Company owns certain common stock with the intention of holding the securities primarily for market appreciation and as such, the changes in the fair value of these securities are recorded through Net investment income. Prior to 2018, equity securities were considered available for sale with changes in fair value reported as a component of Other comprehensive income (loss). The Company's carrying value of investments in limited partnerships is its share of the net asset value of each partnership, as determined by the general partner. Certain partnerships for which results are not available on a timely basis are reported on a lag, primarily three months or less. Changes in net asset values are accounted for under the equity method and recorded within Net investment income on the Consolidated Statements of Operations. Mortgage loans are commercial in nature, are carried at unpaid principal balance, net of unamortized fees and any valuation allowance, and are recorded once funded. Interest income from mortgage loans is recognized on an accrual basis using the effective yield method. Mortgage loans are considered to be impaired loans when it is probable that contractual principal and interest payments will not be collected. The Company evaluates loans for impairment on a specific loan basis and identifies loans for evaluation of impairment based on the collection experience of each loan and other credit quality indicators such as debt service coverage ratio and the creditworthiness of the borrower or tenants of credit tenant loan properties. Accrual of income is generally suspended for mortgage loans that are impaired and collection of principal and interest payments is unlikely. Mortgage loans are considered past due when full principal or interest payments have not been received according to contractual terms. As of December 31, 2018 and 2017 , there were no loans past due or in non-accrual status, and no valuation allowance was recorded. Other invested assets include overseas deposits. Overseas deposits are valued using the net asset value per share (or equivalent) practical expedient. They are primarily short-term government securities, agency securities and corporate bonds held in trusts that are managed by Lloyd's of London. These funds are required of Lloyd's syndicates to protect policyholders in overseas markets and may be denominated in local currency. Short term investments are carried at fair value, with the exception of cash accounts earning interest, which are carried at cost and approximate fair value. Changes in fair value are reported as a component of Other comprehensive income. Purchases and sales of all securities are recorded on the trade date, except for private placement debt securities, including bank loan participations, which are recorded once funded. Realized investment gains and losses are determined on the basis of the cost or amortized cost of the specific securities sold.
Variable Interest Entities	In the normal course of investing activities, the Company enters into relationships with variable interest entities (VIEs), as both an investor in limited partnerships and asset-backed securities issued by third-party VIEs. The Company is not the primary beneficiary of these VIEs, and therefore does not consolidate them. The Company determines whether it is the primary beneficiary of a VIE based on a qualitative assessment of the relative power and benefits of the Company and the other participants in the VIE. The Company’s maximum exposure to loss with respect to these investments is limited to the investment carrying values included in the Company’s Consolidated Balance Sheets and any unfunded commitments.
Impairments, Other Than Temporary	An available for sale security is impaired if the fair value of the security is less than its cost adjusted for accretion, amortization and previously recorded OTTI losses, otherwise defined as an unrealized loss. When a security is impaired, the impairment is evaluated to determine whether it is temporary or other-than-temporary. Significant judgment is required in the determination of whether an OTTI loss has occurred for a security. The Company follows a consistent and systematic process for determining and recording an OTTI loss, including the evaluation of securities in an unrealized loss position on at least a quarterly basis. The Company’s assessment of whether an OTTI loss has occurred incorporates both quantitative and qualitative information. Fixed maturity securities that the Company intends to sell, or it more likely than not will be required to sell before recovery of amortized cost, are considered to be other-than-temporarily impaired and the entire difference between the amortized cost basis and fair value of the security is recognized as an OTTI loss in earnings. The remaining fixed maturity securities in an unrealized loss position are evaluated to determine if a credit loss exists. The factors considered include (a) the financial condition and near-term and long-term prospects of the issuer, (b) whether the debtor is current on interest and principal payments, (c) credit ratings of the securities and (d) general market conditions and industry or sector specific outlook. The Company also considers results and analysis of cash flow modeling for asset-backed securities, and when appropriate, other fixed maturity securities. The focus of the analysis for asset-backed securities is on assessing the sufficiency and quality of underlying collateral and timing of cash flows based on scenario tests. If the present value of the modeled expected cash flows equals or exceeds the amortized cost of a security, no credit loss is judged to exist and the asset-backed security is deemed to be temporarily impaired. If the present value of the expected cash flows is significantly less than amortized cost, the security is judged to be other-than-temporarily impaired for credit reasons and that shortfall, referred to as the credit component, is recognized as an OTTI loss in earnings. The difference between the adjusted amortized cost basis and fair value, referred to as the non-credit component, is recognized as OTTI in Other comprehensive income. In subsequent reporting periods, a change in intent to sell or further credit impairment on a security whose fair value has not deteriorated will cause the non-credit component originally recorded as OTTI in Other comprehensive income to be recognized as an OTTI loss in earnings. The Company performs the discounted cash flow analysis using stressed scenarios to determine future expectations regarding recoverability. Significant assumptions enter into these cash flow projections including delinquency rates, probable risk of default, loss severity upon a default, over collateralization and interest coverage triggers and credit support from lower level tranches.
Deferred Non-Insurance Warranty Revenue	Deferred Non-Insurance Warranty Acquisition Expense Dealers, retailers and agents earn commission for assisting the Company in obtaining non-insurance warranty contracts. Additionally, the Company utilizes a third-party to perform warranty administrator services for its consumer goods warranties. These costs, which are deferred and recorded as Deferred non-insurance warranty acquisition expense, are amortized to Non-insurance warranty expense consistent with how the related revenue is recognized. Losses under warranty contracts shall be recognized when it is probable that estimated future costs exceed unrecognized revenue. The Company evaluates deferred costs for recoverability including consideration of anticipated investment income. Adjustments to deferred costs, if necessary, are recorded in the current period results of operations. Deferred Non-Insurance Warranty Revenue Non-insurance warranty revenue is primarily generated from separately-priced service contracts that provide mechanical breakdown and other coverages to vehicle or consumer goods owners. The warranty contracts generally provide coverage from 1 month to 10 years . For warranty products where the Company acts as the principal in the transaction, Non-insurance warranty revenues are reported on a gross basis, with amounts paid by customers reported as Non-insurance warranty revenue and commissions paid to agents reported as Non-insurance warranty expense. Non-insurance warranty revenue is reported net of any premiums related to contractual liability coverage issued by the Company's insurance operations. Additionally, the Company provides warranty administration services for dealer and manufacturer obligor warranty products, which include limited warranties and guaranteed automobile protection waivers. The Company recognizes Non-insurance warranty revenues over the service period in proportion to the actuarially determined expected claims emergence pattern. Customers pay in full at the inception of the warranty contract. The liability for deferred revenue represents the unearned portion of revenue in advance of the Company's performance. The deferred revenue balance includes amounts which are refundable on a pro rata basis upon cancellation.
Income Taxes	Income Taxes The Company and its eligible subsidiaries (CNA Tax Group) are included in the consolidated federal income tax return of Loews and its eligible subsidiaries. The Company accounts for income taxes under the asset and liability method. Under the asset and liability method, deferred income taxes are recognized for temporary differences between the financial statement and tax return bases of assets and liabilities, based on enacted tax rates and other provisions of the tax law. The effect of a change in tax laws or rates on deferred tax assets and liabilities is recognized in income in the period in which such change is enacted. Future tax benefits are recognized to the extent that realization of such benefits is more likely than not, and a valuation allowance is established for any portion of a deferred tax asset that management believes will not be realized.
Pension and Postretirement Benefits	Pension and Postretirement Benefits The Company recognizes the overfunded or underfunded status of its defined benefit plans in Other assets or Other liabilities on the Consolidated Balance Sheets. Changes in funded status related to prior service costs and credits and actuarial gains and losses are recognized in the year in which the changes occur through Other comprehensive income. Annual service cost, interest cost, expected return on plan assets, amortization of prior service costs and credits and amortization of actuarial gains and losses are recognized in the Consolidated Statements of Operations. The vested benefit obligation for the CNA Retirement Plan is determined based on eligible compensation and accrued service for previously entitled employees. Effective June 30, 2015, future benefit accruals under the CNA Retirement Plan were eliminated and the benefit obligations were frozen.
Stock-Based Compensation	Stock-Based Compensation The Company records compensation expense using the fair value method for all awards it grants, modifies or cancels primarily on a straight-line basis over the requisite service period, generally three years.
Foreign Currency	Foreign Currency The Company's foreign subsidiaries' balance sheet accounts are translated at the exchange rates in effect at each reporting date and income statement accounts are either translated at the exchange rates on the date of the transaction or at average exchange rates. Foreign currency translation gains and losses are reflected in Stockholders' equity as a component of AOCI.
Property and Equipment	Property and Equipment Property and equipment are carried at cost less accumulated depreciation. Depreciation is based on the estimated useful lives of the various classes of property and equipment and is determined principally on the straight-line method. Furniture and fixtures are depreciated over seven years. Office equipment is depreciated over five years. The estimated lives for data processing equipment and software generally range from three to five years, but can be as long as ten years. Leasehold improvements are depreciated over the corresponding lease terms not to exceed the underlying asset life.
Goodwill	Goodwill Goodwill represents the excess of purchase price over the fair value of the net assets of acquired entities and businesses. Goodwill in the International segment may change from period to period as a result of foreign currency translation. Goodwill is tested for impairment annually or when certain triggering events require such tests. As a result of reviews completed for the year ended December 31, 2018 , the Company determined that the estimated fair value of the reporting units were in excess of their carrying value including Goodwill. Changes in future periods in assumptions about the level of economic capital, business growth, earnings projections or the weighted average cost of capital could result in a goodwill impairment.
Other Intangible Assets	Other Intangible Assets Other intangible assets are reported within Other assets. Finite-lived intangible assets are amortized over their estimated useful lives. Indefinite-lived other intangible assets are tested for impairment annually or when certain triggering events require such tests.
Earnings (Loss) Per Share Data	Earnings (Loss) Per Share Data Earnings (loss) per share is based on weighted average number of outstanding common shares. Basic earnings (loss) per share excludes the impact of dilutive securities and is computed by dividing Net income (loss) by the weighted average number of common shares outstanding for the period. Diluted earnings (loss) per share reflects the potential dilution that could occur if securities or other contracts to issue common stock were exercised or converted into common stock. For the years ended December 31, 2018 , 2017 and 2016 , approximately 943 thousand , 988 thousand and 678 thousand potential shares attributable to exercises or conversions into common stock under stock-based employee compensation plans were included in the calculation of diluted earnings per share. For those same periods, 6 thousand , less than 1 thousand and 102 thousand potential shares attributable to exercises or conversions into common stock under stock-based employee compensation plans were not included in the calculation of diluted earnings per share because the effect would have been antidilutive.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Schedule of New Accounting Pronouncements and Changes in Accounting Principles	The cumulative effect changes to the Consolidated Balance Sheet for the adoption of the updated guidance on January 1, 2018 were as follows: (In millions) Balance as of December 31, 2017 Adjustments Due to Adoption of Topic 606 Balance as of January 1, 2018 Deferred non-insurance warranty acquisition expense $ 212 $ 1,882 $ 2,094 Deferred non-insurance warranty revenue 972 1,969 2,941 Deferred income taxes 137 21 158 Retained earnings 9,414 (66 ) 9,348 The impact of adoption on the Consolidated Statements of Operations and Balance Sheet was as follows: Year ended December 31, 2018 Prior to Adoption Effect of Adoption As Reported (In millions) Statement of operations: Non-insurance warranty revenue $ 420 $ 587 $ 1,007 Total revenues 9,547 587 10,134 Non-insurance warranty expense 328 595 923 Total claims, benefits and expenses 8,575 595 9,170 Income before income tax 972 (8 ) 964 Income tax expense (153 ) 2 (151 ) Net income 819 (6 ) 813 Balance sheet (1) at December 31, 2018: Deferred non-insurance warranty acquisition expense $ 2,116 $ 397 $ 2,513 Deferred non-insurance warranty revenue 2,997 405 3,402 Deferred income taxes 390 2 392 Retained earnings 9,283 (6 ) 9,277 (1) The Prior to Adoption amounts presented in this table include the cumulative effect adjustment at adoption presented in the prior table.

Investments (Tables)

Investments (Tables)	12 Months Ended
	Dec. 31, 2018
Investments [Abstract]
Net investment income	The significant components of Net investment income are presented in the following table. Years ended December 31 (In millions) 2018 2017 2016 Fixed maturity securities $ 1,795 $ 1,812 $ 1,819 Equity securities 18 12 10 Limited partnership investments (22 ) 207 155 Mortgage loans 50 34 41 Short term investments 26 15 8 Trading portfolio 7 12 10 Other 4 1 4 Gross investment income 1,878 2,093 2,047 Investment expense (61 ) (59 ) (59 ) Net investment income $ 1,817 $ 2,034 $ 1,988
Net realized investment gains (losses)	Net realized investment gains (losses) are presented in the following table. Years ended December 31 (In millions) 2018 2017 2016 Net realized investment gains (losses): Fixed maturity securities: Gross realized gains $ 168 $ 186 $ 204 Gross realized losses (164 ) (64 ) (138 ) Net realized investment gains (losses) on fixed maturity securities 4 122 66 Equity securities (74 ) — (5 ) Derivatives 9 (4 ) (2 ) Short term investments and other 9 (25 ) (9 ) Net realized investment gains (losses) $ (52 ) $ 93 $ 50
Net change in unrealized gains (losses) on investments	Net change in unrealized gains on investments is presented in the following table. Years ended December 31 (In millions) 2018 2017 2016 Net change in unrealized gains on investments: Fixed maturity securities $ (1,811 ) $ 728 $ 225 Equity securities (1) — 32 (2 ) Other — (2 ) 1 Total net change in unrealized gains on investments $ (1,811 ) $ 758 $ 224 (1) As of January 1, 2018, the Company adopted ASU 2016-01, Financial Instruments - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities . The change in fair value of equity securities is now recognized through the income statement. See Note A to the Consolidated Financial Statements for additional information.
Components of net other than temporary impairment losses recognized in earnings by asset type	The components of OTTI losses recognized in earnings by asset type are presented in the following table. Years ended December 31 (In millions) 2018 2017 2016 Fixed maturity securities available-for-sale: Corporate and other bonds $ 12 $ 12 $ 59 Asset-backed 9 1 13 Total fixed maturity securities available-for-sale 21 13 72 Equity securities available-for-sale — 1 9 OTTI losses recognized in earnings $ 21 $ 14 $ 81
Summary of fixed maturity and equity securities	The following tables present a summary of fixed maturity and equity securities. December 31, 2018 (1) Cost or Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Unrealized OTTI Losses (Gains) (In millions) Fixed maturity securities available-for-sale: Corporate and other bonds $ 18,764 $ 791 $ 395 $ 19,160 $ — States, municipalities and political subdivisions 9,681 1,076 9 10,748 — Asset-backed: Residential mortgage-backed 4,815 68 57 4,826 (20 ) Commercial mortgage-backed 2,200 28 32 2,196 — Other asset-backed 1,975 11 24 1,962 — Total asset-backed 8,990 107 113 8,984 (20 ) U.S. Treasury and obligations of government-sponsored enterprises 156 3 — 159 — Foreign government 480 5 4 481 — Redeemable preferred stock 10 — — 10 — Total fixed maturity securities available-for-sale 38,081 1,982 521 39,542 $ (20 ) Total fixed maturity securities trading 4 — — 4 Total fixed maturity securities $ 38,085 $ 1,982 $ 521 $ 39,546 December 31, 2017 Cost or Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Unrealized OTTI Losses (Gains) (In millions) Fixed maturity securities available-for-sale: Corporate and other bonds $ 17,210 $ 1,625 $ 28 $ 18,807 $ — States, municipalities and political subdivisions 12,478 1,551 2 14,027 (11 ) Asset-backed: Residential mortgage-backed 5,043 109 32 5,120 (27 ) Commercial mortgage-backed 1,840 46 14 1,872 — Other asset-backed 1,083 16 5 1,094 — Total asset-backed 7,966 171 51 8,086 (27 ) U.S. Treasury and obligations of government-sponsored enterprises 111 2 4 109 — Foreign government 437 9 2 444 — Redeemable preferred stock 10 1 — 11 — Total fixed maturity securities available-for-sale 38,212 3,359 87 41,484 $ (38 ) Total fixed maturity securities trading 3 — — 3 Equity securities available-for-sale: Common stock 21 7 1 27 Preferred stock 638 31 1 668 Total equity securities available-for-sale 659 38 2 695 Total fixed maturity and equity securities $ 38,874 $ 3,397 $ 89 $ 42,182 (1) As of January 1, 2018, the Company adopted ASU 2016-01, Financial Instruments - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities . The change in fair value of equity securities is now recognized through the income statement. See Note A to the Consolidated Financial Statements for additional information.
Securities in a gross unrealized loss position	The following tables present the estimated fair value and gross unrealized losses of fixed maturity and equity securities in a gross unrealized loss position by the length of time in which the securities have continuously been in that position. Less than 12 Months 12 Months or Longer Total December 31, 2018 (1) Estimated Fair Value Gross Unrealized Losses Estimated Fair Value Gross Unrealized Losses Estimated Fair Value Gross Unrealized Losses (In millions) Fixed maturity securities available-for-sale: Corporate and other bonds $ 8,543 $ 340 $ 825 $ 55 $ 9,368 $ 395 States, municipalities and political subdivisions 517 8 5 1 522 9 Asset-backed: Residential mortgage-backed 1,932 23 1,119 34 3,051 57 Commercial mortgage-backed 728 10 397 22 1,125 32 Other asset-backed 834 21 125 3 959 24 Total asset-backed 3,494 54 1,641 59 5,135 113 U.S. Treasury and obligations of government-sponsored enterprises 21 — 19 — 40 — Foreign government 114 2 124 2 238 4 Total $ 12,689 $ 404 $ 2,614 $ 117 $ 15,303 $ 521 Less than 12 Months 12 Months or Longer Total December 31, 2017 Estimated Fair Value Gross Unrealized Losses Estimated Fair Value Gross Unrealized Losses Estimated Fair Value Gross Unrealized Losses (In millions) Fixed maturity securities available-for-sale: Corporate and other bonds $ 1,354 $ 21 $ 168 $ 7 $ 1,522 $ 28 States, municipalities and political subdivisions 72 1 85 1 157 2 Asset-backed: Residential mortgage-backed 1,228 5 947 27 2,175 32 Commercial mortgage-backed 403 4 212 10 615 14 Other asset-backed 248 3 18 2 266 5 Total asset-backed 1,879 12 1,177 39 3,056 51 U.S. Treasury and obligations of government-sponsored enterprises 49 2 21 2 70 4 Foreign government 166 2 4 — 170 2 Total fixed maturity securities available-for-sale 3,520 38 1,455 49 4,975 87 Equity securities available-for-sale: Common stock 7 1 — — 7 1 Preferred stock 93 1 — — 93 1 Total equity securities available-for-sale 100 2 — — 100 2 Total $ 3,620 $ 40 $ 1,455 $ 49 $ 5,075 $ 89 (1) As of January 1, 2018, the Company adopted ASU 2016-01, Financial Instruments - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities . The change in fair value of equity securities is now recognized through the income statement. See Note A to the Consolidated Financial Statements for additional information.
Activity related to the pretax fixed maturity credit loss component reflected within retained earnings for securities still held for which a portion of an OTTI loss was recognized in OCI	The following table presents the activity related to the pretax credit loss component reflected in Retained earnings on fixed maturity securities still held as of December 31, 2018 , 2017 and 2016 for which a portion of an OTTI loss was recognized in Other comprehensive income (loss). Years ended December 31 (In millions) 2018 2017 2016 Beginning balance of credit losses on fixed maturity securities $ 27 $ 36 $ 53 Reductions for securities sold during the period (9 ) (9 ) (16 ) Reductions for securities the Company intends to sell or more likely than not will be required to sell — — (1 ) Ending balance of credit losses on fixed maturity securities $ 18 $ 27 $ 36
Contractual maturity	The following table presents available-for-sale fixed maturity securities by contractual maturity. December 31 2018 2017 (In millions) Cost or Amortized Cost Estimated Fair Value Cost or Amortized Cost Estimated Fair Value Due in one year or less $ 1,350 $ 1,359 $ 1,135 $ 1,157 Due after one year through five years 7,979 8,139 8,165 8,501 Due after five years through ten years 16,859 16,870 16,060 16,718 Due after ten years 11,893 13,174 12,852 15,108 Total $ 38,081 $ 39,542 $ 38,212 $ 41,484

Fair Value (Tables)

Fair Value (Tables)	12 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Assets and liabilities measured at fair value on a recurring basis	Assets and liabilities measured at fair value on a recurring basis are presented in the following tables. Corporate bonds and other includes obligations of the U.S. Treasury, government-sponsored enterprises, foreign governments and redeemable preferred stock. December 31, 2018 Total Assets/Liabilities at Fair Value (In millions) Level 1 Level 2 Level 3 Assets Fixed maturity securities: Corporate bonds and other $ 196 $ 19,396 $ 222 $ 19,814 States, municipalities and political subdivisions — 10,748 — 10,748 Asset-backed — 8,787 197 8,984 Total fixed maturity securities 196 38,931 419 39,546 Equity securities: Common stock 144 — 4 148 Non-redeemable preferred stock 48 570 14 632 Total equity securities 192 570 18 780 Short term and other 216 949 — 1,165 Total assets $ 604 $ 40,450 $ 437 $ 41,491 Liabilities Other liabilities $ — $ (4 ) $ — $ (4 ) Total liabilities $ — $ (4 ) $ — $ (4 ) December 31, 2017 Total Assets/Liabilities at Fair Value (In millions) Level 1 Level 2 Level 3 Assets Fixed maturity securities: Corporate bonds and other $ 128 $ 19,148 $ 98 $ 19,374 States, municipalities and political subdivisions — 14,026 1 14,027 Asset-backed — 7,751 335 8,086 Total fixed maturity securities 128 40,925 434 41,487 Equity securities: Common stock 23 — 4 27 Non-redeemable preferred stock 68 584 16 668 Total equity securities 91 584 20 695 Short term and other 396 958 — 1,354 Total assets $ 615 $ 42,467 $ 454 $ 43,536 Liabilities Other liabilities $ — $ 3 $ — $ 3 Total liabilities $ — $ 3 $ — $ 3
Table of reconciliation for assets and liablities measured at fair value on a recurring basis using significant unobservable inputs	The tables below present a reconciliation for all assets and liabilities measured at fair value on a recurring basis using significant unobservable inputs (Level 3). Level 3 (In millions) Corporate bonds and other States, municipalities and political subdivisions Asset-backed Equity securities Derivative financial instruments Total Balance as of January 1, 2018 $ 98 $ 1 $ 335 $ 20 $ — $ 454 Total realized and unrealized investment gains (losses): Reported in Net realized investment gains (losses) (1 ) — 5 (2 ) — 2 Reported in Net investment income — — — — — — Reported in Other comprehensive income (loss) (4 ) — (8 ) — — (12 ) Total realized and unrealized investment gains (losses) (5 ) — (3 ) (2 ) — (10 ) Purchases 117 — 162 — — 279 Sales (5 ) — (72 ) — — (77 ) Settlements (9 ) (1 ) (64 ) — — (74 ) Transfers into Level 3 35 — 42 — — 77 Transfers out of Level 3 (9 ) — (203 ) — — (212 ) Balance as of December 31, 2018 $ 222 $ — $ 197 $ 18 $ — $ 437 Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2018 recognized in Net income (loss) $ — $ — $ (2 ) $ (2 ) $ — $ (4 ) Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2018 recognized in Other comprehensive income (loss) (5 ) — (4 ) — — (9 ) Level 3 (In millions) Corporate bonds and other States, municipalities and political subdivisions Asset-backed Equity securities Derivative financial instruments Life settlement contracts Total Balance as of January 1, 2017 $ 130 $ 1 $ 199 $ 19 $ — $ 58 $ 407 Total realized and unrealized investment gains (losses): Reported in Net realized investment gains (losses) — — 2 — 1 — 3 Reported in Other revenues — — — — — 6 6 Reported in Other comprehensive income (loss) 3 — 3 3 — — 9 Total realized and unrealized investment gains (losses) 3 — 5 3 1 6 18 Purchases 18 — 107 1 — — 126 Sales (5 ) — — (3 ) (1 ) (59 ) (68 ) Settlements (54 ) — (43 ) — — (5 ) (102 ) Transfers into Level 3 16 — 153 — — — 169 Transfers out of Level 3 (10 ) — (86 ) — — — (96 ) Balance as of December 31, 2017 $ 98 $ 1 $ 335 $ 20 $ — $ — $ 454 Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2017 recognized in Net income (loss) $ — $ — $ — $ — $ — $ — $ —
Quantitative information about significant unobservable inputs in the fair value measurement of level 3 assets	The following tables present quantitative information about the significant unobservable inputs utilized by the Company in the fair value measurements of Level 3 assets. Valuations for assets and liabilities not presented in the tables below are primarily based on broker/dealer quotes for which there is a lack of transparency as to inputs used to develop the valuations. The quantitative detail of these unobservable inputs is neither provided nor reasonably available to the Company. The weighted average rate is calculated based on fair value. December 31, 2018 Estimated Fair Value (In millions) Valuation Technique(s) Unobservable Input(s) Range (Weighted Average) Fixed maturity securities $ 228 Discounted cash flow Credit spread 1% - 12% (3%) December 31, 2017 Estimated Fair Value Valuation Technique(s) Unobservable Input(s) Range (Weighted Average) Fixed maturity securities $ 136 Discounted cash flow Credit spread 1% - 12% (3%)
Carrying amount and estimated fair value of financial instrument assets and liabilities not measured at fair value	The carrying amount and estimated fair value of the Company's financial assets and liabilities which are not measured at fair value on the Consolidated Balance Sheets are presented in the following tables. December 31, 2018 Carrying Amount Estimated Fair Value (In millions) Level 1 Level 2 Level 3 Total Assets Mortgage loans $ 839 $ — $ — $ 827 $ 827 Note receivable 35 — — 35 35 Liabilities Long term debt $ 2,680 $ — $ 2,731 $ — $ 2,731 December 31, 2017 Carrying Estimated Fair Value (In millions) Level 1 Level 2 Level 3 Total Assets Mortgage loans $ 839 $ — $ — $ 844 $ 844 Note receivable 46 — — 46 46 Liabilities Short term debt $ 150 $ — $ 150 $ — $ 150 Long term debt 2,708 — 2,896 — 2,896

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Reconcilliation between the Company's federal income tax (expense) benefit at statutory rates and the recorded income tax (expense) benefit	The following table presents a reconciliation between the Company's federal income tax expense at statutory rates and the recorded income tax expense. Years ended December 31 (In millions) 2018 2017 2016 Income tax expense at statutory rates $ (203 ) $ (459 ) $ (398 ) Tax benefit from tax exempt income 63 131 124 Foreign taxes and credits (1 ) 3 3 State income taxes (13 ) (7 ) (6 ) Net deferred tax asset remeasurement 6 (83 ) — Other tax expense (3 ) 4 (1 ) Income tax expense $ (151 ) $ (411 ) $ (278 )
Current and deferred components of the Company's income tax (expense) benefit	The following table presents the current and deferred components of the Company's income tax expense. Years ended December 31 (In millions) 2018 2017 2016 Current tax expense $ (171 ) $ (243 ) $ (142 ) Deferred tax benefit (expense) 20 (168 ) (136 ) Total income tax expense $ (151 ) $ (411 ) $ (278 )
Significant components of the Company's deferred tax assets and liabilities	The deferred tax effects of the significant components of the Company's deferred tax assets and liabilities are presented in the following table. December 31 (In millions) 2018 2017 Deferred Tax Assets: Insurance reserves: Property and casualty claim and claim adjustment expense reserves $ 108 $ 74 Unearned premium reserves 108 142 Receivables 15 15 Employee benefits 143 154 Deferred retroactive reinsurance benefit 79 68 Other assets 131 105 Gross deferred tax assets 584 558 Deferred Tax Liabilities: Investment valuation differences 44 55 Deferred acquisition costs 78 77 Net unrealized gains 14 233 Software and hardware 44 46 Other liabilities 12 10 Gross deferred tax liabilities 192 421 Net deferred tax asset $ 392 $ 137

Claim and Claim Adjustment Ex_2

Claim and Claim Adjustment Expense Reserves (Tables)	12 Months Ended
	Dec. 31, 2018
Net Incurred Claim and Claim Adjustment Expense [Line Items]
Schedule of liability for unpaid claims and claims adjustment expense	The following table presents a reconciliation between beginning and ending claim and claim adjustment expense reserves, including claim and claim adjustment expense reserves of the Life & Group segment. As of or for the years ended December 31 (In millions) 2018 2017 2016 Reserves, beginning of year: Gross $ 22,004 $ 22,343 $ 22,663 Ceded 3,934 4,094 4,087 Net reserves, beginning of year 18,070 18,249 18,576 Net incurred claim and claim adjustment expenses: Provision for insured events of current year 5,358 5,201 5,025 Decrease in provision for insured events of prior years (179 ) (381 ) (342 ) Amortization of discount 176 179 175 Total net incurred (1) 5,355 4,999 4,858 Net payments attributable to: Current year events (1,046 ) (975 ) (967 ) Prior year events (4,285 ) (4,366 ) (4,167 ) Total net payments (5,331 ) (5,341 ) (5,134 ) Foreign currency translation adjustment and other (129 ) 163 (51 ) Net reserves, end of year 17,965 18,070 18,249 Ceded reserves, end of year 4,019 3,934 4,094 Gross reserves, end of year $ 21,984 $ 22,004 $ 22,343 (1) Total net incurred above does not agree to Insurance claims and policyholders' benefits as reflected on the Consolidated Statements of Operations due to amounts related to retroactive reinsurance deferred gain accounting, uncollectible reinsurance and loss deductible receivables, and benefit expenses related to future policy benefits, which are not reflected in the table above.
Gross and net carried claim and claim adjustment expense reserves	The following tables present the gross and net carried reserves. December 31, 2018 Specialty Commercial International Life & Group Corporate & Other Total (In millions) Gross Case Reserves $ 1,623 $ 4,181 $ 867 $ 3,516 $ 1,208 $ 11,395 Gross IBNR Reserves 3,842 4,562 883 85 1,217 10,589 Total Gross Carried Claim and Claim Adjustment Expense Reserves $ 5,465 $ 8,743 $ 1,750 $ 3,601 $ 2,425 $ 21,984 Net Case Reserves $ 1,483 $ 3,831 $ 749 $ 3,364 $ 96 $ 9,523 Net IBNR Reserves 3,348 4,167 775 56 96 8,442 Total Net Carried Claim and Claim Adjustment Expense Reserves $ 4,831 $ 7,998 $ 1,524 $ 3,420 $ 192 $ 17,965 December 31, 2017 Specialty Commercial International Life & Group Corporate & Other Total (In millions) Gross Case Reserves $ 1,742 $ 4,427 $ 744 $ 3,386 $ 1,371 $ 11,670 Gross IBNR Reserves 3,927 4,337 892 113 1,065 10,334 Total Gross Carried Claim and Claim Adjustment Expense Reserves $ 5,669 $ 8,764 $ 1,636 $ 3,499 $ 2,436 $ 22,004 Net Case Reserves $ 1,600 $ 4,103 $ 640 $ 3,208 $ 94 $ 9,645 Net IBNR Reserves 3,407 4,033 792 82 111 8,425 Total Net Carried Claim and Claim Adjustment Expense Reserves $ 5,007 $ 8,136 $ 1,432 $ 3,290 $ 205 $ 18,070
Net prior year development	The following table presents development recorded for the Specialty, Commercial, International and Corporate & Other segments. December 31, 2018 (In millions) 2018 2017 2016 Pretax (favorable) unfavorable development: Specialty $ (150 ) $ (174 ) $ (247 ) Commercial (25 ) (115 ) 15 International (4 ) (9 ) (58 ) Corporate & Other (2 ) (10 ) 2 Total pretax (favorable) unfavorable development $ (181 ) $ (308 ) $ (288 )
Short-duration insurance contracts, reconciliation of claims development to liability	The table below reconciles the net liability for unpaid claim and claim adjustment expenses to the amount presented in the Consolidated Balance Sheets. As of December 31 (In millions) 2018 Net liability for unpaid claim and claim adjustment expenses: Specialty $ 4,831 Commercial 7,998 International 1,524 Corporate & Other 192 Life & Group (1) 3,420 Total net claim and claim adjustment expenses 17,965 Reinsurance receivables: (2) Specialty 634 Commercial 745 International 226 Corporate & Other (3) 2,233 Life & Group 181 Total reinsurance receivables 4,019 Total gross liability for unpaid claim and claim adjustment expenses $ 21,984 (1) The Life & Group segment amounts are primarily related to long term care claim reserves, but also includes amounts related to unfunded structured settlements arising from short duration contracts. Long term care policies are long duration contracts. (2) Reinsurance receivables presented do not include reinsurance receivables related to paid losses. (3) The Corporate & Other Reinsurance receivables are primarily related to A&EP claims covered under the Loss Portfolio Transfer.
Specialty
Net Incurred Claim and Claim Adjustment Expense [Line Items]
Net prior year claim and allocated claim adjustment expense reserve development	The following table presents further detail of the development recorded for the Specialty segment. Years ended December 31 (In millions) 2018 2017 2016 Pretax (favorable) unfavorable development: Medical Professional Liability $ 47 $ 30 $ 9 Other Professional Liability and Management Liability (127 ) (126 ) (140 ) Surety (70 ) (84 ) (63 ) Warranty (10 ) 4 4 Other 10 2 (57 ) Total pretax (favorable) unfavorable development $ (150 ) $ (174 ) $ (247 )
Short-duration insurance contracts, reconciliation of claims development to liability	The table below provides the line of business composition of the net liability for unpaid claim and claim adjustment expenses for the Specialty segment. As of December 31 (In millions) 2018 Net liability for unpaid claim and claim adjustment expenses: Medical Professional Liability $ 1,457 Other Professional Liability and Management Liability 2,849 Surety 379 Warranty 40 Other 106 Total net liability for unpaid claim and claim adjustment expenses $ 4,831
Commercial
Net Incurred Claim and Claim Adjustment Expense [Line Items]
Net prior year claim and allocated claim adjustment expense reserve development	The following table presents further detail of the development recorded for the Commercial segment. Years ended December 31 (In millions) 2018 2017 2016 Pretax (favorable) unfavorable development: Commercial Auto $ 1 $ (35 ) $ (47 ) General Liability 32 (24 ) (65 ) Workers' Compensation (32 ) (63 ) 145 Property and Other (26 ) 7 (18 ) Total pretax (favorable) unfavorable development $ (25 ) $ (115 ) $ 15
Short-duration insurance contracts, reconciliation of claims development to liability	The table below provides the line of business composition of the net liability for unpaid claim and claim adjustment expenses for the Commercial segment. As of December 31 (In millions) 2018 Net Claim and claim adjustment expenses: Commercial Auto $ 412 General Liability 3,195 Workers' Compensation 3,968 Property and Other 423 Total net liability for claim and claim adjustment expenses $ 7,998
International
Net Incurred Claim and Claim Adjustment Expense [Line Items]
Net prior year claim and allocated claim adjustment expense reserve development	The following table presents further detail of the development recorded for the International segment. Years ended December 31 (In millions) 2018 2017 2016 Pretax (favorable) unfavorable development: Casualty $ (17 ) $ 9 $ (29 ) Property 17 (16 ) (21 ) Energy and Marine (19 ) (12 ) (18 ) Specialty 27 12 19 Healthcare and Technology (12 ) (2 ) (9 ) Total pretax (favorable) unfavorable development $ (4 ) $ (9 ) $ (58 )
Short-duration insurance contracts, reconciliation of claims development to liability	The table below provides the composition of the net liability for unpaid claim and claim adjustment expenses for the International segment. As of December 31 (In millions) 2018 Net Claim and claim adjustment expenses: International excluding Hardy $ 1,059 Hardy 465 Total net liability for claim and claim adjustment expenses $ 1,524
CNAF Consolidated
Net Incurred Claim and Claim Adjustment Expense [Line Items]
Schedule of historical claims duration	The table below presents information about average historical claims duration as of December 31, 2018 and is presented as required supplementary information, which is unaudited. Average Annual Percentage Payout of Ultimate Net Incurred Claim and Allocated Claim Adjustment Expenses in Year: 1 2 3 4 5 6 7 8 9 10 Total Specialty Medical Professional Liability 3.8 % 19.7 % 24.3 % 20.1 % 12.1 % 7.2 % 4.5 % 2.5 % 1.0 % 2.9 % 98.1 % Other Professional Liability and Management Liability 6.2 % 21.5 % 21.3 % 17.4 % 10.7 % 6.4 % 5.8 % 2.9 % 3.3 % 2.1 % 97.6 % Surety (1) 21.6 % 37.9 % 21.0 % 7.9 % 2.1 % 1.6 % (1.7 )% (0.5 )% — % — % 89.9 % Commercial Commercial Auto 28.0 % 23.0 % 18.5 % 14.2 % 9.3 % 3.1 % 1.3 % 0.3 % 0.2 % 0.7 % 98.6 % General Liability 4.3 % 15.9 % 19.5 % 20.5 % 15.7 % 8.0 % 5.6 % 3.2 % 1.6 % 0.8 % 95.1 % Workers' Compensation 13.7 % 21.1 % 13.9 % 10.6 % 7.5 % 4.4 % 4.4 % 3.2 % 2.5 % 1.2 % 82.5 % International International - Excluding Hardy 20.5 % 26.0 % 11.2 % 7.1 % 6.5 % 4.8 % 4.3 % 2.8 % 1.7 % 3.7 % 88.6 % International - Hardy (2) 24.0 % 38.9 % 13.3 % 6.0 % 2.9 % 2.1 % 87.2 % (1) Due to the nature of the Surety business, average annual percentage payout of ultimate net incurred claim and allocated claim adjustment expenses has been calculated using only the payouts of mature accident years presented in the loss reserve development tables. (2) Average historical claims duration for Hardy is presented prospectively beginning with the first full year subsequent to acquisition, 2013.
Impact of loss portfolio transfer on the consolidated statement of operations	The following table presents the impact of the Loss Portfolio Transfer on the Consolidated Statements of Operations. Years ended December 31 (In millions) 2018 2017 2016 Additional amounts ceded under LPT: Net A&EP adverse development before consideration of LPT $ 178 $ 60 $ 200 Provision for uncollectible third-party reinsurance on A&EP (16 ) — — Total additional amounts ceded under LPT 162 60 200 Retroactive reinsurance benefit recognized (114 ) (68 ) (107 ) Pretax impact of deferred retroactive reinsurance $ 48 $ (8 ) $ 93
Hardy | International
Net Incurred Claim and Claim Adjustment Expense [Line Items]
Short-duration contracts net incurred claims and allocated claim adjustment expenses	Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses are presented in the following table. As of December 31 Calendar Year As of December 31, 2018 (In millions, except reported claims data) Net Claim and Allocated Claim Adjustment Expense Reserves at Acquisition Net Incurred Claim and Allocated Claim Adjustment Expenses in 2012 (1)(2) Total Acquired Net Claim and Allocated Claim Adjustment Expense Reserves and 2012 Incurreds 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 IBNR Cumulative Number of Claims Accident Year 2009 $ 11 $ — $ 12 $ 6 $ (4 ) $ 1 $ (2 ) $ (3 ) $ (3 ) $ (2 ) 3,856 2010 48 (9 ) 38 47 52 46 52 51 50 — 4,540 2011 125 (1 ) 124 134 134 138 137 137 140 (2 ) 6,252 2012 33 71 104 104 112 119 113 113 115 1 6,900 2013 130 146 138 139 140 144 4 7,624 2014 184 182 176 170 170 2 8,097 2015 190 179 177 178 3 8,968 2016 227 245 234 28 9,536 2017 244 252 48 10,309 2018 270 103 7,563 Total $ 1,550 $ 185
Short-duration contracts net cumulative paid claim adjustment expenses reconciliation of total liability for unpaid claim and claim adjustment expense	Cumulative Net Paid Claims and Allocated Claim Adjustment Expenses are presented in the following table. As of December 31 Calendar Year (In millions) 2012 (1)(2) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 Accident Year 2009 $ 2 $ (2 ) $ (4 ) $ (4 ) $ (4 ) $ (5 ) $ (4 ) 2010 19 35 42 45 47 48 46 2011 30 83 123 127 131 132 134 2012 14 79 100 109 106 109 110 2013 38 101 120 126 130 133 2014 56 122 141 150 155 2015 29 98 129 144 2016 63 144 171 2017 53 150 2018 55 Total $ 1,094 Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented $ 456 Net liability for unpaid claim and claim adjustment expenses for accident years prior to 2009 — Liability for unallocated claim adjustment expenses for accident years presented 9 Total net liability for unpaid claim and claim adjustment expenses $ 465
Short-duration contracts reserve development	Net strengthening or (releases) of prior accident year reserves is presented in the following table. For the years ended December 31 Calendar Year (In millions) 2012 (1)(2) 2013 (1) 2014 (1) 2015 (1)(3) 2016 (1)(3) 2017 (1)(3) 2018 (3) Total (3) Accident Year 2009 $ 1 $ (6 ) $ (10 ) $ 5 $ (3 ) $ (1 ) $ — $ (14 ) 2010 (10 ) 9 5 (6 ) 6 (1 ) (1 ) 2 2011 (1 ) 10 — 4 (1 ) — 3 15 2012 — 8 7 (6 ) — 2 11 2013 16 (8 ) 1 1 4 14 2014 (2 ) (6 ) (6 ) — (14 ) 2015 (11 ) (2 ) 1 (12 ) 2016 18 (11 ) 7 2017 8 8 (1) Data presented for these calendar years is required supplemental information, which is unaudited. (2) Data presented for this calendar year is post-acquisition of Hardy. (3) The amounts included in the loss reserve development tables above are presented at the year-end 2018 foreign currency exchange rates for all periods presented to remove the effects of foreign currency exchange rate fluctuations between calendar years. The amounts included within the table on page 102 presenting the detail of the development recorded within the International segment include the impact of fluctuations in foreign currency exchange rates.
Medical Professional Liability | Specialty
Net Incurred Claim and Claim Adjustment Expense [Line Items]
Short-duration contracts net incurred claims and allocated claim adjustment expenses	Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses are presented in the following table. As of December 31 Calendar Year As of December 31, 2018 (In millions, except reported claims data) 2009 (1) 2010 (1) 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 IBNR Cumulative Number of Claims Accident Year 2009 $ 389 $ 390 $ 392 $ 392 $ 366 $ 346 $ 336 $ 309 $ 302 $ 310 $ — 14,716 2010 402 412 423 426 415 395 365 360 356 — 14,615 2011 429 437 443 468 439 434 437 437 8 16,505 2012 464 469 508 498 493 484 493 10 17,691 2013 462 479 500 513 525 535 28 19,442 2014 450 489 537 530 535 30 19,602 2015 433 499 510 494 78 17,835 2016 427 487 485 120 15,427 2017 412 449 217 13,777 2018 404 333 11,205 Total $ 4,498 $ 824
Short-duration contracts net cumulative paid claim adjustment expenses reconciliation of total liability for unpaid claim and claim adjustment expense	Cumulative Net Paid Claims and Allocated Claim Adjustment Expenses are presented in the following table. As of December 31 Calendar Year (In millions) 2009 (1) 2010 (1) 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 Accident Year 2009 $ 9 $ 63 $ 143 $ 211 $ 247 $ 269 $ 280 $ 288 $ 291 $ 300 2010 10 86 173 257 306 326 337 346 350 2011 17 109 208 295 347 375 398 409 2012 14 117 221 323 388 427 457 2013 17 119 255 355 414 462 2014 23 136 258 359 417 2015 22 101 230 313 2016 18 121 246 2017 19 107 2018 21 Total $ 3,082 Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented $ 1,416 Net liability for unpaid claim and claim adjustment expenses for accident years prior to 2009 18 Liability for unallocated claim adjustment expenses for accident years presented 23 Total net liability for unpaid claim and claim adjustment expenses $ 1,457
Short-duration contracts reserve development	Net strengthening or (releases) of prior accident year reserves is presented in the following table. For the years ended December 31 Calendar Year (In millions) 2010 (1) 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 Total Accident Year 2009 $ 1 $ 2 $ — $ (26 ) $ (20 ) $ (10 ) $ (27 ) $ (7 ) $ 8 $ (79 ) 2010 10 11 3 (11 ) (20 ) (30 ) (5 ) (4 ) (46 ) 2011 8 6 25 (29 ) (5 ) 3 — 8 2012 5 39 (10 ) (5 ) (9 ) 9 29 2013 17 21 13 12 10 73 2014 39 48 (7 ) 5 85 2015 66 11 (16 ) 61 2016 60 (2 ) 58 2017 37 37 Total net development for the accident years presented above 60 58 47 Total net development for accident years prior to 2009 (51 ) (21 ) 1 Total unallocated claim adjustment expense development — (7 ) (1 ) Total $ 9 $ 30 $ 47 (1) Data presented for these calendar years is required supplemental information, which is unaudited.
Other Professional Liability and Management Liability | Specialty
Net Incurred Claim and Claim Adjustment Expense [Line Items]
Short-duration contracts net incurred claims and allocated claim adjustment expenses	Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses are presented in the following table. As of December 31 Calendar Year As of December 31, 2018 (In millions, except reported claims data) 2009 (1) 2010 (1) 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 IBNR Cumulative Number of Claims Accident Year 2009 $ 831 $ 875 $ 908 $ 903 $ 893 $ 903 $ 897 $ 906 $ 904 $ 892 $ 18 17,374 2010 828 828 848 848 847 837 824 827 821 19 17,888 2011 880 908 934 949 944 911 899 888 39 18,728 2012 923 909 887 878 840 846 833 41 18,491 2013 884 894 926 885 866 863 65 17,918 2014 878 898 885 831 835 88 17,515 2015 888 892 877 832 194 17,333 2016 901 900 900 279 17,787 2017 847 845 479 17,780 2018 850 726 16,564 Total $ 8,559 $ 1,948
Short-duration contracts net cumulative paid claim adjustment expenses reconciliation of total liability for unpaid claim and claim adjustment expense	Cumulative Net Paid Claims and Allocated Claim Adjustment Expenses are presented in the following table. As of December 31 Calendar Year (In millions) 2009 (1) 2010 (1) 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 Accident Year 2009 $ 37 $ 195 $ 361 $ 553 $ 641 $ 722 $ 772 $ 801 $ 825 $ 844 2010 31 204 405 541 630 670 721 752 784 2011 71 314 503 605 683 726 781 796 2012 56 248 400 573 651 711 755 2013 54 249 447 618 702 754 2014 51 223 392 515 647 2015 60 234 404 542 2016 64 248 466 2017 57 222 2018 54 Total $ 5,864 Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented $ 2,695 Net liability for unpaid claim and claim adjustment expenses for accident years prior to 2009 90 Liability for unallocated claim adjustment expenses for accident years presented 64 Total net liability for unpaid claim and claim adjustment expenses $ 2,849
Short-duration contracts reserve development	Net strengthening or (releases) of prior accident year reserves is presented in the following table. For the years ended December 31 Calendar Year (In millions) 2010 (1) 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 Total Accident Year 2009 $ 44 $ 33 $ (5 ) $ (10 ) $ 10 $ (6 ) $ 9 $ (2 ) $ (12 ) $ 61 2010 — 20 — (1 ) (10 ) (13 ) 3 (6 ) (7 ) 2011 28 26 15 (5 ) (33 ) (12 ) (11 ) 8 2012 (14 ) (22 ) (9 ) (38 ) 6 (13 ) (90 ) 2013 10 32 (41 ) (19 ) (3 ) (21 ) 2014 20 (13 ) (54 ) 4 (43 ) 2015 4 (15 ) (45 ) (56 ) 2016 (1 ) — (1 ) 2017 (2 ) (2 ) Total net development for the accident years presented above (125 ) (94 ) (88 ) Total net development for accident years prior to 2009 (15 ) (25 ) (32 ) Total unallocated claim adjustment expense development — (7 ) (7 ) Total $ (140 ) $ (126 ) $ (127 ) (1) Data presented for these calendar years is required supplemental information, which is unaudited.
Surety | Specialty
Net Incurred Claim and Claim Adjustment Expense [Line Items]
Short-duration contracts net incurred claims and allocated claim adjustment expenses	Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses are presented in the following table. As of December 31 Calendar Year As of December 31, 2018 (In millions, except reported claims data) 2009 (1) 2010 (1) 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 IBNR Cumulative Number of Claims Accident Year 2009 $ 114 $ 114 $ 103 $ 85 $ 68 $ 59 $ 52 $ 53 $ 53 $ 52 $ 1 6,688 2010 112 112 111 84 76 66 63 59 61 1 5,971 2011 120 121 116 87 75 70 66 62 1 5,808 2012 120 122 98 70 52 45 39 2 5,559 2013 120 121 115 106 91 87 6 5,039 2014 123 124 94 69 60 19 5,036 2015 131 131 104 79 36 4,887 2016 124 124 109 60 5,185 2017 120 115 78 4,936 2018 114 101 3,105 Total $ 778 $ 305
Short-duration contracts net cumulative paid claim adjustment expenses reconciliation of total liability for unpaid claim and claim adjustment expense	Cumulative Net Paid Claims and Allocated Claim Adjustment Expenses are presented in the following table. As of December 31 Calendar Year (In millions) 2009 (1) 2010 (1) 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 Accident Year 2009 $ 13 $ 24 $ 34 $ 41 $ 43 $ 45 $ 46 $ 47 $ 47 $ 47 2010 13 34 50 55 57 58 55 52 52 2011 19 42 55 58 60 60 56 57 2012 5 32 34 35 35 36 37 2013 16 40 69 78 78 78 2014 7 30 38 36 38 2015 7 26 38 40 2016 5 37 45 2017 23 37 2018 5 Total $ 436 Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented $ 342 Net liability for unpaid claim and claim adjustment expenses for accident years prior to 2009 7 Liability for unallocated claim adjustment expenses for accident years presented 30 Total net liability for unpaid claim and claim adjustment expenses $ 379
Short-duration contracts reserve development	Net strengthening or (releases) of prior accident year reserves is presented in the following table. For the years ended December 31 Calendar Year (In millions) 2010 (1) 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 Total Accident Year 2009 $ — $ (11 ) $ (18 ) $ (17 ) $ (9 ) $ (7 ) $ 1 $ — $ (1 ) $ (62 ) 2010 — (1 ) (27 ) (8 ) (10 ) (3 ) (4 ) 2 (51 ) 2011 1 (5 ) (29 ) (12 ) (5 ) (4 ) (4 ) (58 ) 2012 2 (24 ) (28 ) (18 ) (7 ) (6 ) (81 ) 2013 1 (6 ) (9 ) (15 ) (4 ) (33 ) 2014 1 (30 ) (25 ) (9 ) (63 ) 2015 — (27 ) (25 ) (52 ) 2016 — (15 ) (15 ) 2017 (5 ) (5 ) Total net development for the accident years presented above (64 ) (82 ) (67 ) Total net development for accident years prior to 2009 1 1 (3 ) Total unallocated claim adjustment expense development — (3 ) — Total $ (63 ) $ (84 ) $ (70 ) (1) Data presented for these calendar years is required supplemental information, which is unaudited.
Commercial Auto | Commercial
Net Incurred Claim and Claim Adjustment Expense [Line Items]
Short-duration contracts net incurred claims and allocated claim adjustment expenses	Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses are presented in the following table. As of December 31 Calendar Year As of December 31, 2018 (In millions, except reported claims data) 2009 (1) 2010 (1) 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 IBNR Cumulative Number of Claims Accident Year 2009 $ 291 $ 276 $ 280 $ 282 $ 285 $ 281 $ 278 $ 276 $ 276 $ 277 $ — 48,499 2010 267 283 287 291 298 293 289 288 288 1 48,030 2011 268 281 288 302 300 294 294 294 4 47,905 2012 275 289 299 303 307 299 299 6 46,288 2013 246 265 265 249 245 245 7 39,429 2014 234 223 212 205 205 9 33,609 2015 201 199 190 190 22 30,388 2016 198 186 186 27 30,342 2017 199 198 45 30,580 2018 229 118 28,602 Total $ 2,411 $ 239
Short-duration contracts net cumulative paid claim adjustment expenses reconciliation of total liability for unpaid claim and claim adjustment expense	Cumulative Net Paid Claims and Allocated Claim Adjustment Expenses are presented in the following table. As of December 31 Calendar Year (In millions) 2009 (1) 2010 (1) 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 Accident Year 2009 $ 73 $ 130 $ 191 $ 233 $ 261 $ 272 $ 274 $ 274 $ 275 $ 277 2010 74 141 203 246 271 281 286 287 287 2011 79 145 199 248 274 284 287 289 2012 78 160 220 259 282 285 290 2013 74 135 168 200 225 234 2014 64 102 137 166 187 2015 52 96 130 153 2016 52 93 126 2017 58 107 2018 66 Total $ 2,016 Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented $ 395 Net liability for unpaid claim and claim adjustment expenses for accident years prior to 2009 6 Liability for unallocated claim adjustment expenses for accident years presented 11 Total net liability for unpaid claim and claim adjustment expenses $ 412
Short-duration contracts reserve development	Net strengthening or (releases) of prior accident year reserves is presented in the following table. For the years ended December 31 Calendar Year (In millions) 2010 (1) 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 Total Accident Year 2009 $ (15 ) $ 4 $ 2 $ 3 $ (4 ) $ (3 ) $ (2 ) $ — $ 1 $ (14 ) 2010 16 4 4 7 (5 ) (4 ) (1 ) — 21 2011 13 7 14 (2 ) (6 ) — — 26 2012 14 10 4 4 (8 ) — 24 2013 19 — (16 ) (4 ) — (1 ) 2014 (11 ) (11 ) (7 ) — (29 ) 2015 (2 ) (9 ) — (11 ) 2016 (12 ) — (12 ) 2017 (1 ) (1 ) Total net development for the accident years presented above (37 ) (41 ) — Total net development for accident years prior to 2009 (10 ) 4 — Total unallocated claim adjustment expense development — 2 1 Total $ (47 ) $ (35 ) $ 1 (1) Data presented for these calendar years is required supplemental information, which is unaudited.
General Liability | Commercial
Net Incurred Claim and Claim Adjustment Expense [Line Items]
Short-duration contracts net incurred claims and allocated claim adjustment expenses	Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses are presented in the following table. As of December 31 Calendar Year As of December 31, 2018 (In millions, except reported claims data) 2009 (1) 2010 (1) 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 IBNR Cumulative Number of Claims Accident Year 2009 $ 662 $ 716 $ 733 $ 755 $ 752 $ 756 $ 755 $ 754 $ 755 $ 755 $ 16 44,934 2010 646 664 658 709 750 726 697 691 691 24 44,144 2011 591 589 631 677 676 681 670 669 26 39,283 2012 587 611 639 636 619 635 635 46 35,083 2013 650 655 650 655 613 623 51 33,420 2014 653 658 654 631 635 71 27,736 2015 581 576 574 589 122 23,471 2016 623 659 667 265 23,078 2017 632 632 412 19,716 2018 653 553 13,336 Total $ 6,549 $ 1,586
Short-duration contracts net cumulative paid claim adjustment expenses reconciliation of total liability for unpaid claim and claim adjustment expense	Cumulative Net Paid Claims and Allocated Claim Adjustment Expenses are presented in the following table. As of December 31 Calendar Year (In millions) 2009 (1) 2010 (1) 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 Accident Year 2009 $ 33 $ 124 $ 305 $ 468 $ 576 $ 625 $ 663 $ 701 $ 721 $ 727 2010 27 145 280 429 561 611 642 652 656 2011 28 148 273 411 517 568 602 622 2012 28 132 247 374 454 510 559 2013 31 128 240 352 450 510 2014 31 119 247 376 481 2015 19 110 230 357 2016 32 163 279 2017 23 118 2018 33 Total $ 4,342 Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented $ 2,207 Net liability for unpaid claim and claim adjustment expenses for accident years prior to 2009 927 Liability for unallocated claim adjustment expenses for accident years presented 61 Total net liability for unpaid claim and claim adjustment expenses $ 3,195
Short-duration contracts reserve development	Net strengthening or (releases) of prior accident year reserves is presented in the following table. For the years ended December 31 Calendar Year (In millions) 2010 (1) 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 Total Accident Year 2009 $ 54 $ 17 $ 22 $ (3 ) $ 4 $ (1 ) $ (1 ) $ 1 $ — $ 93 2010 18 (6 ) 51 41 (24 ) (29 ) (6 ) — 45 2011 (2 ) 42 46 (1 ) 5 (11 ) (1 ) 78 2012 24 28 (3 ) (17 ) 16 — 48 2013 5 (5 ) 5 (42 ) 10 (27 ) 2014 5 (4 ) (23 ) 4 (18 ) 2015 (5 ) (2 ) 15 8 2016 36 8 44 2017 — — Total net development for the accident years presented above (46 ) (31 ) 36 Total net development for accident years prior to 2009 (19 ) (1 ) — Total unallocated claim adjustment expense development — 8 (4 ) Total $ (65 ) $ (24 ) $ 32 (1) Data presented for these calendar years is required supplemental information, which is unaudited.
Workers' Compensation | Commercial
Net Incurred Claim and Claim Adjustment Expense [Line Items]
Short-duration contracts net incurred claims and allocated claim adjustment expenses	Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses are presented in the following table. As of December 31 Calendar Year As of December 31, 2018 (In millions, except reported claims data) 2009 (1) 2010 (1) 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 IBNR Cumulative Number of Claims Accident Year 2009 $ 592 $ 599 $ 609 $ 611 $ 616 $ 626 $ 631 $ 638 $ 649 $ 650 $ 46 51,822 2010 583 632 654 676 698 710 730 733 732 44 49,106 2011 607 641 647 659 651 676 676 674 27 45,637 2012 601 627 659 669 678 673 671 59 42,477 2013 537 572 592 618 593 582 86 38,665 2014 467 480 479 452 450 104 33,465 2015 422 431 406 408 146 31,828 2016 426 405 396 171 31,905 2017 440 432 171 32,811 2018 450 276 30,399 Total $ 5,445 $ 1,130
Short-duration contracts net cumulative paid claim adjustment expenses reconciliation of total liability for unpaid claim and claim adjustment expense	Cumulative Net Paid Claims and Allocated Claim Adjustment Expenses are presented in the following table. As of December 31 Calendar Year (In millions) 2009 (1) 2010 (1) 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 Accident Year 2009 $ 89 $ 227 $ 321 $ 388 $ 443 $ 476 $ 503 $ 525 $ 549 $ 557 2010 97 251 359 442 510 542 577 615 625 2011 99 249 358 438 478 522 564 571 2012 87 232 342 416 470 509 524 2013 80 213 300 370 417 419 2014 61 159 215 258 282 2015 51 131 180 212 2016 53 129 169 2017 63 151 2018 68 Total $ 3,578 Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented $ 1,867 Net liability for unpaid claim and claim adjustment expenses for accident years prior to 2009 2,131 Other (2) (32 ) Liability for unallocated claim adjustment expenses for accident years presented 2 Total net liability for unpaid claim and claim adjustment expenses $ 3,968
Short-duration contracts reserve development	Net strengthening or (releases) of prior accident year reserves is presented in the following table. For the years ended December 31 Calendar Year (In millions) 2010 (1) 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 Total Accident Year 2009 $ 7 $ 10 $ 2 $ 5 $ 10 $ 5 $ 7 $ 11 $ 1 $ 58 2010 49 22 22 22 12 20 3 (1 ) 149 2011 34 6 12 (8 ) 25 — (2 ) 67 2012 26 32 10 9 (5 ) (2 ) 70 2013 35 20 26 (25 ) (11 ) 45 2014 13 (1 ) (27 ) (2 ) (17 ) 2015 9 (25 ) 2 (14 ) 2016 (21 ) (9 ) (30 ) 2017 (8 ) (8 ) Total net development for the accident years presented above 95 (89 ) (32 ) Adjustment for development on a discounted basis (3 ) (3 ) — Total net development for accident years prior to 2009 53 28 7 Total unallocated claim adjustment expense development — 1 (7 ) Total $ 145 $ (63 ) $ (32 ) (1) Data presented for these calendar years is required supplemental information, which is unaudited. (2) Other includes the effect of discounting lifetime claim reserves.
Excluding Hardy | International
Net Incurred Claim and Claim Adjustment Expense [Line Items]
Short-duration contracts net incurred claims and allocated claim adjustment expenses	Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses are presented in the following table. As of December 31 Calendar Year As of December 31, 2018 (In millions, except reported claims data) 2009 (1) 2010 (1) 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 IBNR Cumulative Number of Claims Accident Year 2009 $ 254 $ 251 $ 253 $ 253 $ 239 $ 236 $ 226 $ 218 $ 216 $ 219 $ 8 20,257 2010 232 229 223 217 208 201 195 188 184 8 21,949 2011 265 266 258 239 227 221 219 216 9 24,585 2012 266 273 258 251 251 244 236 20 24,975 2013 287 289 281 261 257 250 25 23,909 2014 275 290 290 279 271 38 24,874 2015 289 305 304 286 51 23,239 2016 284 302 289 79 17,557 2017 300 363 134 17,865 2018 369 174 16,565 Total $ 2,683 $ 546
Short-duration contracts net cumulative paid claim adjustment expenses reconciliation of total liability for unpaid claim and claim adjustment expense	Cumulative Net Paid Claims and Allocated Claim Adjustment Expenses are presented in the following table. As of December 31 Calendar Year (In millions) 2009 (1) 2010 (1) 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 Accident Year 2009 $ 39 $ 92 $ 122 $ 137 $ 153 $ 162 $ 174 $ 185 $ 190 $ 198 2010 48 96 119 133 146 156 164 167 169 2011 44 114 135 149 162 174 181 185 2012 43 112 144 164 180 191 201 2013 49 112 138 155 169 179 2014 51 120 148 165 182 2015 55 131 161 181 2016 66 131 157 2017 64 145 2018 90 Total $ 1,687 Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented $ 996 Net liability for unpaid claim and claim adjustment expenses for accident years prior to 2009 39 Liability for unallocated claim adjustment expenses for accident years presented 24 Total net liability for unpaid claim and claim adjustment expenses $ 1,059
Short-duration contracts reserve development	Net strengthening or (releases) of prior accident year reserves is presented in the following table. For the years ended December 31 Calendar Year (In millions) 2010 (1) 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1)(2) 2016 (1)(2) 2017 (1)(2) 2018 (2) Total (2) Accident Year 2009 $ (3 ) $ 2 $ — $ (14 ) $ (3 ) $ (10 ) $ (8 ) $ (2 ) $ 3 $ (35 ) 2010 (3 ) (6 ) (6 ) (9 ) (7 ) (6 ) (7 ) (4 ) (48 ) 2011 1 (8 ) (19 ) (12 ) (6 ) (2 ) (3 ) (49 ) 2012 7 (15 ) (7 ) — (7 ) (8 ) (30 ) 2013 2 (8 ) (20 ) (4 ) (7 ) (37 ) 2014 15 — (11 ) (8 ) (4 ) 2015 16 (1 ) (18 ) (3 ) 2016 18 (13 ) 5 2017 63 63 (1) Data presented for these calendar years is required supplemental information, which is unaudited. (2) The amounts included in the loss reserve development tables above are presented at the year-end 2018 foreign currency exchange rates for all periods presented to remove the effects of foreign currency exchange rate fluctuations between calendar years. The amounts included within the table on page 102 presenting the detail of the development recorded within the International segment include the impact of fluctuations in foreign currency exchange rates.

Reinsurance (Tables)

Reinsurance (Tables)	12 Months Ended
	Dec. 31, 2018
Reinsurance Disclosures [Abstract]
Components of Reinsurance Receivables	The following table presents the amounts receivable from reinsurers. December 31 (In millions) 2018 2017 Reinsurance receivables related to insurance reserves: Ceded claim and claim adjustment expenses $ 4,019 $ 3,934 Ceded future policy benefits 233 230 Reinsurance receivables related to paid losses 203 126 Reinsurance receivables 4,455 4,290 Allowance for uncollectible reinsurance (29 ) (29 ) Reinsurance receivables, net of allowance for uncollectible reinsurance $ 4,426 $ 4,261
Components of Earned and Written Premiums	The effects of reinsurance on earned premiums and written premiums are presented in the following tables. (In millions) Direct Assumed Ceded Net Assumed/ Net % 2018 Earned Premiums Property and casualty $ 10,857 $ 305 $ 4,380 $ 6,782 4.5 % Long term care 480 50 — 530 9.4 % Total earned premiums $ 11,337 $ 355 $ 4,380 $ 7,312 4.9 % 2017 Earned Premiums Property and casualty $ 10,447 $ 317 $ 4,315 $ 6,449 4.9 % Long term care 489 50 — 539 9.3 % Total earned premiums $ 10,936 $ 367 $ 4,315 $ 6,988 5.3 % 2016 Earned Premiums Property and casualty $ 10,400 $ 258 $ 4,270 $ 6,388 4.0 % Long term care 486 50 — 536 9.3 % Total earned premiums $ 10,886 $ 308 $ 4,270 $ 6,924 4.4 % (In millions) Direct Assumed Ceded Net Assumed/ Net % 2018 Written Premiums Property and casualty $ 11,094 $ 310 $ 4,583 $ 6,821 4.5 % Long term care 474 50 — 524 9.5 % Total written premiums $ 11,568 $ 360 $ 4,583 $ 7,345 4.9 % 2017 Written Premiums Property and casualty $ 10,655 $ 327 $ 4,449 $ 6,533 5.0 % Long term care 486 50 — 536 9.3 % Total written premiums $ 11,141 $ 377 $ 4,449 $ 7,069 5.3 % 2016 Written Premiums Property and casualty $ 10,451 $ 245 $ 4,255 $ 6,441 3.8 % Long term care 495 52 — 547 9.5 % Total written premiums $ 10,946 $ 297 $ 4,255 $ 6,988 4.3 %

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Schedule of debt instruments	Debt is composed of the following obligations. December 31 (In millions) 2018 2017 Short term debt: Senior notes of CNAF, 6.950%, face amount of $150, due January 15, 2018 $ — $ 150 Long term debt: Senior notes of CNAF: 5.875%, face amount of $500, due August 15, 2020 499 498 5.750%, face amount of $400, due August 15, 2021 399 398 3.950%, face amount of $550, due May 15, 2024 547 547 4.500%, face amount of $500, due March 1, 2026 498 498 3.450%, face amount of $500, due August 15, 2027 495 495 Debenture of CNAF, 7.250%, face amount of $243, due November 15, 2023 242 242 Subordinated variable rate debt of Hardy, face amount of $30, due September 15, 2036 (1) — 30 Total long term debt 2,680 2,708 Total debt $ 2,680 $ 2,858 (1) In the third quarter of 2018, the Company redeemed $30 million of subordinated variable rate debt of Hardy due September 15, 2036.
Maturity of debt	The combined aggregate maturities for debt as of December 31, 2018 are presented in the following table. (In millions) 2019 $ — 2020 500 2021 400 2022 — 2023 243 Thereafter 1,550 Less discount (13 ) Total $ 2,680

Benefit Plans (Tables)

Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2018
Retirement Benefits [Abstract]
Funded status	The following table presents a reconciliation of benefit obligations and plan assets. Pension Benefits Postretirement Benefits (In millions) 2018 2017 2018 2017 Benefit obligation as of January 1 $ 2,749 $ 2,729 $ 11 $ 15 Changes in benefit obligation: Service cost — — — — Interest cost 93 103 — — Participants' contributions — — 3 4 Actuarial (gain) loss (187 ) 99 — (1 ) Benefits paid (166 ) (170 ) (5 ) (7 ) Foreign currency translation and other (7 ) 10 — — Settlements (16 ) (22 ) — — Benefit obligation as of December 31 2,466 2,749 9 11 Fair value of plan assets as of January 1 2,261 2,193 — — Change in plan assets: Actual return on plan assets (69 ) 221 — — Company contributions 23 29 2 3 Participants' contributions — — 3 4 Benefits paid (166 ) (170 ) (5 ) (7 ) Foreign currency translation and other (8 ) 10 — — Settlements (16 ) (22 ) — — Fair value of plan assets as of December 31 2,025 2,261 — — Funded status $ (441 ) $ (488 ) $ (9 ) $ (11 ) Amounts recognized on the Consolidated Balance Sheets as of December 31: Other assets $ 9 $ 4 $ — $ — Other liabilities (450 ) (492 ) (9 ) (11 ) Net amount recognized $ (441 ) $ (488 ) $ (9 ) $ (11 ) Amounts recognized in Accumulated other comprehensive income, not yet recognized in net periodic cost (benefit): Prior service credit $ — $ — $ — $ (2 ) Net actuarial (gain) loss 984 987 (3 ) (4 ) Net amount recognized $ 984 $ 987 $ (3 ) $ (6 )
Components of net periodic cost (benefit)	The components of net periodic pension cost (benefit) are presented in the following table. Years ended December 31 (In millions) 2018 2017 2016 Net periodic pension cost (benefit) Service cost $ — $ — $ — Non-service cost (benefit): Interest cost on projected benefit obligation 93 103 113 Expected return on plan assets (159 ) (154 ) (160 ) Amortization of net actuarial (gain) loss 37 35 37 Settlement loss 6 9 — Total non-service cost (benefit) (23 ) (7 ) (10 ) Total net periodic pension cost (benefit) $ (23 ) $ (7 ) $ (10 ) The components of net periodic postretirement cost (benefit) are presented in the following table. Years ended December 31 (In millions) 2018 2017 2016 Net periodic postretirement cost (benefit) Service cost $ — $ — $ — Non-service cost (benefit): Amortization of prior service credit (1 ) (2 ) (2 ) Amortization of net actuarial (gain) loss (1 ) — — Total non-service cost (benefit) (2 ) (2 ) (2 ) Total net periodic postretirement cost (benefit) $ (2 ) $ (2 ) $ (2 )
Schedule of amounts recognized in Other comprehensive income	The amounts recognized in Other comprehensive income are presented in the following table. Years ended December 31 (In millions) 2018 2017 2016 Pension and postretirement benefits Amounts arising during the period $ (41 ) $ (31 ) $ (29 ) Settlement 6 9 (2 ) Reclassification adjustment relating to prior service credit (2 ) (2 ) (2 ) Reclassification adjustment relating to actuarial loss 36 35 37 Total increase (decrease) in Other comprehensive income $ (1 ) $ 11 $ 4
Schedule of estimated amounts to be recognized from Accumulated other comprehensive income into net periodic cost (benefit) during next fiscal year	The amounts recognized in Other comprehensive income are presented in the following table. Years ended December 31 (In millions) 2018 2017 2016 Pension and postretirement benefits Amounts arising during the period $ (41 ) $ (31 ) $ (29 ) Settlement 6 9 (2 ) Reclassification adjustment relating to prior service credit (2 ) (2 ) (2 ) Reclassification adjustment relating to actuarial loss 36 35 37 Total increase (decrease) in Other comprehensive income $ (1 ) $ 11 $ 4
Actuarial assumptions for benefit obligations and for net cost or benefit	Actuarial assumptions used for the CNA Retirement Plan and CNA Health and Group Benefits Program to determine benefit obligations are presented in the following table. The interest crediting rate is the weighted average interest rate applied to the individual pension balances for employees who elected to cease accruals effective December 31, 1999. December 31 2018 2017 Pension benefits Discount rate 4.250 % 3.550 % Expected long term rate of return 7.500 7.500 Interest crediting rate 5.000 5.000 Postretirement benefits Discount rate 3.550 % 2.750 % Actuarial assumptions used for the CNA Retirement Plan and CNA Health and Group Benefits Program to determine net cost or benefit are presented in the following table. Years ended December 31 2018 2017 2016 Pension benefits Discount rate 3.550 % 3.950 % 4.150 % Expected long term rate of return 7.500 7.500 7.500 Interest crediting rate 5.000 5.000 5.000 Postretirement benefits Discount rate 2.750 % 2.750 % 2.750 %
Fair value of plan assets measured on a recurring basis	Pension plan assets measured at fair value on a recurring basis as well as cash are presented in the following tables. December 31, 2018 (In millions) Level 1 Level 2 Level 3 Total Assets Fixed maturity securities: Corporate bonds and other $ — $ 472 $ 10 $ 482 States, municipalities and political subdivisions — 58 — 58 Asset-backed — 165 — 165 Total fixed maturity securities — 695 10 705 Equity securities 331 110 — 441 Short term investments 27 54 — 81 Other assets — 9 — 9 Total assets measured at fair value $ 358 $ 868 $ 10 1,236 Total limited partnerships measured at net asset value (1) 789 Total plan assets $ 2,025 December 31, 2017 (In millions) Level 1 Level 2 Level 3 Total Assets Fixed maturity securities: Corporate bonds and other $ — $ 522 $ 10 $ 532 States, municipalities and political subdivisions — 62 — 62 Asset-backed — 180 — 180 Total fixed maturity securities — 764 10 774 Equity securities 405 122 — 527 Short term investments 23 11 — 34 Other assets — 9 — 9 Cash 13 — — 13 Total assets measured at fair value $ 441 $ 906 $ 10 1,357 Total limited partnerships measured at net asset value (1) 904 Total plan assets $ 2,261 (1) Certain investments that are measured at fair value using the net asset value per share (or its equivalent) practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in this table for these investments are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the Plan's Statement of Financial Position.
Schedule of expected benefit payments	The table below presents the estimated future minimum benefit payments to participants as of December 31, 2018 . (In millions) Pension Benefits Postretirement Benefits 2019 $ 175 $ 2 2020 174 2 2021 175 1 2022 177 1 2023 177 1 2024-2028 850 2

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Restricted shares, performance-based restricted share units and performance share unit activity	The following table presents activity for non-vested RSUs and performance share units under the Plan in 2018 . Number of Awards Weighted-Average Grant Date Fair Value Balance as of January 1, 2018 2,070,737 $ 38.92 Awards granted 840,961 51.64 Awards vested (463,725 ) 38.62 Awards forfeited, canceled or expired (307,719 ) 40.59 Performance-based adjustment 63,894 52.00 Balance as of December 31, 2018 2,204,148 43.98

Other Intangible Assets (Tables

Other Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2018
Intangible Assets, Gross (Excluding Goodwill) [Abstract]
Schedule of Other Intangible Assets	Other intangible assets are presented in the following table. December 31 2018 2017 (In millions) Economic Useful Life Carrying Amount Accumulated Amortization Carrying Amount Accumulated Amortization Finite-lived intangible assets: Trade name 8 years $ 6 $ 5 $ 7 $ 5 Distribution channel 15 years 10 4 11 4 Total finite-lived intangible assets 16 9 18 9 Indefinite-lived intangible assets: Syndicate capacity 45 47 Agency force 16 16 Total indefinite-lived intangible assets 61 63 Total other intangible assets $ 77 $ 9 $ 81 $ 9

Operating Leases (Tables)

Operating Leases (Tables)	12 Months Ended
	Dec. 31, 2018
Leases, Operating [Abstract]
Future minimum lease payments	The table below presents the expected future minimum lease payments to be made under non-cancelable operating leases as of December 31, 2018 . (In millions) Future Minimum Lease Payments 2019 $ 35 2020 39 2021 41 2022 38 2023 32 Thereafter 200 Total $ 385

Stockholders' Equity and Stat_2

Stockholders' Equity and Statutory Accounting Practices (Tables)	12 Months Ended
	Dec. 31, 2018
Stockholders' Equity and Statutory Accounting Practices [Abstract]
Combined statutory capital and surplus and net income (loss)	Combined statutory capital and surplus and statutory net income (loss) for the Combined Continental Casualty Companies are presented in the table below, determined in accordance with accounting practices prescribed or permitted by insurance and/or other regulatory authorities Statutory Capital and Surplus Statutory Net Income (Loss) December 31 Years ended December 31 (In millions) 2018 (1) 2017 2018 (1) 2017 2016 Combined Continental Casualty Companies $ 10,411 $ 10,726 $ 1,405 $ 1,029 $ 1,033 (1) Information derived from the statutory-basis financial statements to be filed with insurance regulators.

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Income (Loss) by Component (Tables)	12 Months Ended
	Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated Other Comprehensive Income (Loss) by Component	The tables below display the changes in Accumulated other comprehensive income (loss) by component. (In millions) Net unrealized gains (losses) on investments with OTTI losses Net unrealized gains (losses) on other investments Pension and postretirement benefits Cumulative foreign currency translation adjustment Total Balance as of January 1, 2018, as previously reported $ 25 $ 750 $ (645 ) $ (98 ) $ 32 Cumulative effect adjustment from accounting change for adoption of ASU 2018-02 (1) 5 137 (130 ) — 12 Cumulative effect adjustment from accounting change for adoption of ASU 2016-01 (1) net of tax (expense) benefit of $-, $8, $-, $- and $8 — (28 ) — — (28 ) Balance as of January 1, 2018, as adjusted 30 859 (775 ) (98 ) 16 Other comprehensive income (loss) before reclassifications (7 ) (801 ) (32 ) (82 ) (922 ) Amounts reclassified from accumulated other comprehensive income (loss) net of tax (expense) benefit of $(2), $2, $8, $- and $8 7 (3 ) (32 ) — (28 ) Other comprehensive income (loss) net of tax (expense) benefit of $4, $211, $1, $- and $216 (14 ) (798 ) — (82 ) (894 ) Balance as of December 31, 2018 $ 16 $ 61 $ (775 ) $ (180 ) $ (878 ) (1) See Note A to the Consolidated Financial Statements for additional information. (In millions) Net unrealized gains (losses) on investments with OTTI losses Net unrealized gains (losses) on other investments Pension and postretirement benefits Cumulative foreign currency translation adjustment Total Balance as of January 1, 2017 $ 30 $ 642 $ (647 ) $ (198 ) $ (173 ) Other comprehensive income (loss) before reclassifications (3 ) 190 (25 ) 100 262 Amounts reclassified from accumulated other comprehensive income (loss) net of tax (expense) benefit of $(1), $(38), $15, $- and $(24) 2 82 (27 ) — 57 Other comprehensive income (loss) net of tax (expense) benefit of $2, $(68), $(9), $- and $(75) (5 ) 108 2 100 205 Balance as of December 31, 2017 $ 25 $ 750 $ (645 ) $ (98 ) $ 32
Reclassification out of Accumulated Other Comprehensive Income	Amounts reclassified from Accumulated other comprehensive income (loss) shown above are reported in Net income (loss) as follows: Component of AOCI Consolidated Statements of Operations Line Item Affected by Reclassifications Net unrealized gains (losses) on investments with OTTI losses Net realized investment gains (losses) Net unrealized gains (losses) on other investments Net realized investment gains (losses) Pension and postretirement benefits Other operating expenses and Insurance claims and policyholders' benefits

Business Segments (Tables)

Business Segments (Tables)	12 Months Ended
	Dec. 31, 2018
Segment Reporting [Abstract]
Significant components of the Company's continuing operations and selected balance sheet items	The Company's results of operations and selected balance sheet items by segment are presented in the following tables. Year ended December 31, 2018 Specialty Commercial International Life & Group Corporate & Other (In millions) Eliminations Total Net written premiums $ 2,744 $ 3,060 $ 1,018 $ 524 $ — $ (1 ) $ 7,345 Operating revenues Net earned premiums $ 2,732 $ 3,050 $ 1,001 $ 530 $ — $ (1 ) $ 7,312 Net investment income 439 500 57 801 20 — 1,817 Non-insurance warranty revenue 1,007 — — — — — 1,007 Other revenues 2 28 1 2 19 (2 ) 50 Total operating revenues 4,180 3,578 1,059 1,333 39 (3 ) 10,186 Claims, benefits and expenses Net incurred claims and benefits 1,526 2,053 699 1,218 51 — 5,547 Policyholders’ dividends 5 20 — — — — 25 Amortization of deferred acquisition costs 599 505 231 — — — 1,335 Non-insurance warranty expense 923 — — — — — 923 Other insurance related expenses 279 505 135 122 (1 ) (1 ) 1,039 Other expenses 46 43 14 7 193 (2 ) 301 Total claims, benefits and expenses 3,378 3,126 1,079 1,347 243 (3 ) 9,170 Core income (loss) before income tax 802 452 (20 ) (14 ) (204 ) — 1,016 Income tax (expense) benefit on core income (loss) (173 ) (95 ) 1 57 39 — (171 ) Core income (loss) $ 629 $ 357 $ (19 ) $ 43 $ (165 ) $ — 845 Net realized investment gains (losses) (52 ) Income tax (expense) benefit on net realized investment gains (losses) 14 Net realized investment gains (losses), after tax (38 ) Net deferred tax asset remeasurement 6 Net income $ 813 December 31, 2018 (In millions) Reinsurance receivables $ 649 $ 795 $ 250 $ 414 $ 2,347 $ — $ 4,455 Insurance receivables 947 1,277 284 9 (152 ) — 2,365 Deferred acquisition costs 308 230 95 — — — 633 Goodwill 117 — 29 — — — 146 Deferred non-insurance warranty acquisition expense 2,513 — — — — — 2,513 Insurance reserves Claim and claim adjustment expenses 5,465 8,743 1,750 3,601 2,425 — 21,984 Unearned premiums 2,132 1,454 475 122 — — 4,183 Future policy benefits — — — 10,597 — — 10,597 Deferred non-insurance warranty revenue 3,402 — — — — — 3,402 Year ended December 31, 2017 Specialty Commercial International Life & Group Corporate & Other (In millions) Eliminations Total Net written premiums $ 2,731 $ 2,922 $ 881 $ 536 $ — $ (1 ) $ 7,069 Operating revenues Net earned premiums $ 2,712 $ 2,881 $ 857 $ 539 $ — $ (1 ) $ 6,988 Net investment income 522 658 52 782 20 — 2,034 Non-insurance warranty revenue 390 — — — — — 390 Other revenues 1 32 — 2 2 — 37 Total operating revenues 3,625 3,571 909 1,323 22 (1 ) 9,449 Claims, benefits and expenses Net incurred claims and benefits 1,533 1,930 575 1,269 (19 ) — 5,288 Policyholders’ dividends 4 18 — — — — 22 Amortization of deferred acquisition costs 590 481 162 — — — 1,233 Non-insurance warranty expense 299 — — — — — 299 Other insurance related expenses 279 530 162 129 (1 ) (1 ) 1,098 Other expenses 43 57 (7 ) 7 192 — 292 Total claims, benefits and expenses 2,748 3,016 892 1,405 172 (1 ) 8,232 Core income (loss) before income tax 877 555 17 (82 ) (150 ) — 1,217 Income tax (expense) benefit on core income (loss) (295 ) (186 ) (9 ) 132 60 — (298 ) Core income (loss) $ 582 $ 369 $ 8 $ 50 $ (90 ) $ — 919 Net realized investment gains (losses) 93 Income tax (expense) benefit on net realized investment gains (losses) (30 ) Net realized investment gains (losses), after tax 63 Net deferred tax asset remeasurement (83 ) Net income $ 899 December 31, 2017 (In millions) Reinsurance receivables $ 671 $ 654 $ 212 $ 438 $ 2,315 $ — $ 4,290 Insurance receivables 969 1,103 254 8 2 — 2,336 Deferred acquisition costs 318 223 93 — — — 634 Goodwill 117 — 31 — — — 148 Deferred non-insurance warranty acquisition expense 212 — — — — — 212 Insurance reserves Claim and claim adjustment expenses 5,669 8,764 1,636 3,499 2,436 — 22,004 Unearned premiums 2,020 1,409 472 128 — — 4,029 Future policy benefits — — — 11,179 — — 11,179 Deferred non-insurance warranty revenue 972 — — — — — 972 Year ended December 31, 2016 Specialty Commercial Life & Group Corporate & Other (In millions) International Eliminations Total Net written premiums $ 2,738 $ 2,883 $ 821 $ 547 $ — $ (1 ) $ 6,988 Operating revenues Net earned premiums $ 2,743 $ 2,840 $ 806 $ 536 $ — $ (1 ) $ 6,924 Net investment income 497 657 51 767 16 — 1,988 Non-insurance warranty revenue 361 — — — — — 361 Other revenues 1 32 — (2 ) 12 — 43 Total operating revenues 3,602 3,529 857 1,301 28 (1 ) 9,316 Claims, benefits and expenses Net incurred claims and benefits 1,489 1,905 492 1,286 98 — 5,270 Policyholders’ dividends 4 9 — — — — 13 Amortization of deferred acquisition costs 586 475 174 — — — 1,235 Non-insurance warranty expense 271 — — — — — 271 Other insurance related expenses 295 566 133 132 (3 ) (1 ) 1,122 Other expenses 41 36 24 8 209 — 318 Total claims, benefits and expenses 2,686 2,991 823 1,426 304 (1 ) 8,229 Core income (loss) before income tax 916 538 34 (125 ) (276 ) — 1,087 Income tax (expense) benefit on core income (loss) (310 ) (183 ) (13 ) 145 98 — (263 ) Core income (loss) $ 606 $ 355 $ 21 $ 20 $ (178 ) $ — 824 Net realized investment gains (losses) 50 Income tax (expense) benefit on net realized investment gains (losses) (15 ) Net realized investment gains (losses), after tax 35 Net income $ 859
Revenues by line of business	The following table presents operating revenue by line of business for each reportable segment. Years ended December 31 (In millions) 2018 2017 2016 Specialty Management & Professional Liability $ 2,440 $ 2,533 $ 2,562 Surety 571 541 529 Warranty & Alternative Risks (1) 1,169 551 511 Specialty revenues 4,180 3,625 3,602 Commercial Middle Market 2,045 1,965 1,823 Small Business 472 480 582 Other Commercial Insurance 1,061 1,126 1,124 Commercial revenues 3,578 3,571 3,529 International Canada 255 224 203 Europe 363 326 314 Hardy 441 359 340 International revenues 1,059 909 857 Life & Group revenues 1,333 1,323 1,301 Corporate & Other revenues 39 22 28 Eliminations (3 ) (1 ) (1 ) Total operating revenues 10,186 9,449 9,316 Net realized investment gains (losses) (52 ) 93 50 Total revenues $ 10,134 $ 9,542 $ 9,366 (1) As of January 1, 2018, the Company adopted ASU 2014-09 Revenue Recognition (Topic 606): Revenue from Contracts with Customers . See Note A to the Consolidated Financial Statements for additional information.

Quarterly Financial Data (Una_2

Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Data [Abstract]
Schedule of quarterly financial information	The following tables present unaudited quarterly financial data. 2018 (In millions, except per share data) First Second Third Fourth Full Year Revenues $ 2,535 $ 2,574 $ 2,622 $ 2,403 $ 10,134 Net income (loss) (1) $ 291 $ 270 $ 336 $ (84 ) $ 813 Basic earnings (loss) per share $ 1.07 $ 0.99 $ 1.24 $ (0.31 ) $ 2.99 Diluted earnings (loss) per share $ 1.07 $ 0.99 $ 1.23 $ (0.31 ) $ 2.98 2017 (In millions, except per share data) First Second Third Fourth Full Year Revenues $ 2,330 $ 2,366 $ 2,398 $ 2,448 $ 9,542 Net income (loss) (2)(3) $ 260 $ 272 $ 144 $ 223 $ 899 Basic earnings (loss) per share $ 0.96 $ 1.01 $ 0.53 $ 0.82 $ 3.32 Diluted earnings (loss) per share $ 0.96 $ 1.00 $ 0.53 $ 0.82 $ 3.30 (1) Net income (loss) in the fourth quarter of 2018 included a loss on limited partnership and common stock investments of $109 million and catastrophe losses, net of reinsurance, of $107 million related to Hurricane Michael and the California wildfires. (2) Net income (loss) in the third quarter of 2017 included catastrophe losses, net of reinsurance and including reinstatement premiums, of $188 million related to Hurricanes Harvey, Irma and Maria. (3) Net income (loss) in the fourth quarter of 2017 included a one-time non-cash increase to Income tax expense of $83 million as a result of Tax Reform Legislation.

Summary of Significant Accoun_4

Summary of Significant Accounting Policies (Narrative) (Details) - USD ($) shares in Thousands, $ in Millions	Jan. 01, 2018	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2019	Jan. 01, 2017	Jan. 01, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Anticipated amounts due from insureds related to losses under deductible policies			$ 1,200	$ 1,200
Structured settlement annuities, interest rate, high end			8.00%	8.00%
Discounted reserves for unfunded structured settlements			$ 512	$ 527
Discounted reserves for unfunded structure settlements, discount amount			760	798
Amount of interest recognized on the discounted reserves of unfunded structured settlements			$ 40	$ 41	$ 42
Interest rates at which workers' compensation lifetime claim reserves are discounted at			3.50%	3.50%
Workers' compensation liability			$ 343	$ 346
Discounted reserves for workers’ compensation lifetime claim reserves, discount amount			168	190
Amount of interest accretion recognized on the discounted reserves of workers’ compensation lifetime claim reserves			$ 16	$ 19	17
Long term care claim reserves discounted interest rate			6.00%	6.00%
Discounted reserves for long term care claim reserves			$ 2,600	$ 2,400
Discounted reserves for long term care claim reserves, discount amount			460	$ 446
Minimum interest rate used to calculate reserves for long term care products		6.60%		6.60%
Maximum interest rate used to calculate reserves for long term care products		7.00%		7.00%
Liability balance for guaranty fund			$ 108	$ 121
Percentage of billed receivables compared to total reinsurance receivable			5.00%
Deposit assets			$ 3	8
Deposit liabilities			3	4
Loss on life settlement contracts, held for sale					10
Increase (decrease) in shadow adjustment, net of tax			(333)	397
Reduction of net unrealized gains on investments included in AOCI due to shadow adjustments			1,078	1,411
Foreign currency transaction gain (loss), before tax			$ 1	$ 27	$ (9)
Weighted average number diluted shares outstanding adjustment			943	988	678
Antidilutive securities excluded from computation of earnings per share, amount			6	1	102
Interest paid, net			$ 145	$ 155	$ 157
Income taxes paid			$ 308	$ 152	170
Structured settlement annuities, interest rate, low end			5.50%	5.50%
Furniture and Fixtures
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Property, plant and equipment, useful life			7 years
Office Equipment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Property, plant and equipment, useful life			5 years
Computer Software, Intangible Asset
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Property, plant and equipment, useful life			10 years
Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Warranty coverage term			1 month
Requisite service period for stock- based compensation expense			3 years
Minimum | Computer Software, Intangible Asset
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Property, plant and equipment, useful life			3 years
Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Warranty coverage term			10 years
Maximum | Computer Software, Intangible Asset
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Property, plant and equipment, useful life			5 years
CNAF Consolidated | Loews
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Noncontrolling interest, ownership percentage by parent			89.00%
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustments from changes in accounting guidance, net of tax	$ (50)						$ 0	$ 0
Accumulated Other Comprehensive (Loss) Income
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustments from changes in accounting guidance, net of tax	(16)						$ 0	$ 0
ASU 2016-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustments from changes in accounting guidance, net of tax	(28)
ASU 2016-01 | Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustments from changes in accounting guidance, net of tax	28
ASU 2018-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustments from changes in accounting guidance, net of tax	12
Net unrealized gains (losses) on investments	142
Increase (decrease) in obligation, pension and other postretirement benefits	(130)
ASU 2018-02 | Accumulated Other Comprehensive (Loss) Income
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustments from changes in accounting guidance, net of tax	$ 12
Other assets
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Note receivable			$ 35	$ 46
Preferred stock
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Equity securities, FV-NI, gain (loss)			73
Preferred stock | ASU 2016-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Equity securities, FV-NI, gain (loss)			74
Other comprehensive income (loss), securities, available-for-sale, unrealized holding gain (loss) arising during period, after tax (less than)				32	(6)
Common Stock
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Equity securities, FV-NI, gain (loss)			24
Common Stock | ASU 2016-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Equity securities, FV-NI, gain (loss)			$ 22
Other comprehensive income (loss), securities, available-for-sale, unrealized holding gain (loss) arising during period, after tax (less than)				$ 1	$ 4
Scenario, Forecast | ASU 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease, right-of-use asset						$ 230
Operating lease, liability						$ 230

Summary of Significant Accoun_5

Summary of Significant Accounting Policies (Cumulative Effect to the Consolidated Balance Sheet) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred non-insurance warranty acquisition expense	$ 2,513	$ 2,094	$ 212
Deferred non-insurance warranty revenue	3,402	2,941	972
Deferred income taxes	392	158	137
Retained earnings	9,277	9,348	9,414
Balance as of December 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred non-insurance warranty acquisition expense	2,116		212
Deferred non-insurance warranty revenue	2,997		972
Deferred income taxes	390		137
Retained earnings	9,283		$ 9,414
Adjustments Due to Adoption of Topic 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred non-insurance warranty acquisition expense	397	1,882
Deferred non-insurance warranty revenue	405	1,969
Deferred income taxes	2	21
Retained earnings	$ (6)	$ (66)

Summary of Significant Accoun_6

Summary of Significant Accounting Policies (Impact of adoption on the Consolidated Statements of Operations and Balance Sheet) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Non-insurance warranty revenue									$ 1,007	$ 390	$ 361
Revenues	$ 2,403	$ 2,622	$ 2,574	$ 2,535	$ 2,448	$ 2,398	$ 2,366	$ 2,330	10,134	9,542	9,366
Non-insurance warranty expense									923	299	271
Total claims, benefits and expenses									9,170	8,232	8,229
Income before income tax									964	1,310	1,137
Income tax expense									(151)	(411)	(278)
Net income	(84)	$ 336	$ 270	$ 291	223	$ 144	$ 272	$ 260	813	899	$ 859
Deferred non-insurance warranty acquisition expense	2,513				212				2,513	212		$ 2,094
Deferred non-insurance warranty revenue	3,402				972				3,402	972		2,941
Deferred income taxes	392				137				392	137		158
Retained earnings	9,277				9,414				9,277	9,414		9,348
Prior to Adoption
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Non-insurance warranty revenue									420
Revenues									9,547
Non-insurance warranty expense									328
Total claims, benefits and expenses									8,575
Income before income tax									972
Income tax expense									(153)
Net income									819
Deferred non-insurance warranty acquisition expense	2,116				212				2,116	212
Deferred non-insurance warranty revenue	2,997				972				2,997	972
Deferred income taxes	390				137				390	137
Retained earnings	9,283				$ 9,414				9,283	$ 9,414
Effect of Adoption
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Non-insurance warranty revenue									587
Revenues									587
Non-insurance warranty expense									595
Total claims, benefits and expenses									595
Income before income tax									(8)
Income tax expense									2
Net income									(6)
Deferred non-insurance warranty acquisition expense	397								397			1,882
Deferred non-insurance warranty revenue	405								405			1,969
Deferred income taxes	2								2			21
Retained earnings	$ (6)								$ (6)			$ (66)

Investments (Net investment inc

Investments (Net investment income) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Net Investment Income [Line Items]
Gross investment income	$ 1,878	$ 2,093	$ 2,047
Investment expense	(61)	(59)	(59)
Net investment income	1,817	2,034	1,988
Fixed maturity securities
Net Investment Income [Line Items]
Gross investment income	1,795	1,812	1,819
Equity securities
Net Investment Income [Line Items]
Gross investment income	18	12	10
Limited partnership investments
Net Investment Income [Line Items]
Gross investment income	(22)	207	155
Mortgage loans
Net Investment Income [Line Items]
Gross investment income	50	34	41
Short term investments
Net Investment Income [Line Items]
Gross investment income	26	15	8
Trading portfolio
Net Investment Income [Line Items]
Gross investment income	7	12	10
Other
Net Investment Income [Line Items]
Gross investment income	$ 4	$ 1	$ 4

Investments (Narrative) (Detail

Investments (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Gain (Loss) on Securities [Line Items]
Non-income producing fixed maturity securities	$ 0	$ 2,000,000
Investments that exceed ten percent of stockholders' equity	0	0
Limited partnership investments	1,982,000,000	2,369,000,000
Undistributed earnings of limited partnership investments	$ 153,000,000	$ 539,000,000
Percentage of limited partnerships reported on a current basis	60.00%
Percentage of limited partnerships reported on a one month lag	14.00%
Percentage of limited partnerships employing hedge fund strategies focused on fixed income and equity investments	65.00%	71.00%
Limited partnerships invested in private debt and equity	30.00%	25.00%
Percentage of equity related limited partnership hedge fund strategies	60.00%
Percentage of multistrategy approach limited partnership hedge fund strategies	18.00%
Percentage of distressed investments limited partnership hedge fund strategies	19.00%
Percentage of fixed income limited partnership hedge fund strategies	3.00%
Carrying value of ten largest limited partnerships	$ 876,000,000	$ 1,136,000,000
Carrying value of limited partnerships as percentage of aggregate partnership equity	2.00%	3.00%
Income as percentage of change in partnership equity for all limited partnerships	3.00%	3.00%	4.00%
Obligation to return cash	$ 0	$ 0
RIght to reclaim cash	0	0
Derivative, notional amount	172,000,000	167,000,000
Derivative asset	4,000,000
Derivative liability, fair value, gross liability		(3,000,000)
Future capital call commitments for limited partnership investments	574,000,000
Mortgage loan commitments	59,000,000
Commitments to purchase or fund privately placed debt securities	230,000,000
Commitments to sell various privately placed debt securities	78,000,000
Carrying value of securities deposited under requirements of regulatory authorities	2,500,000,000	2,600,000,000
Cash and securities deposited as collateral for letters of credit	1,000,000,000	1,100,000,000
Senior notes of CNAF, 6.950%, face amount of $150, due November, 2019 | Senior Notes
Gain (Loss) on Securities [Line Items]
Realized investment gains (losses)		(42,000,000)
Face amount		$ 350,000,000
Common Stock
Gain (Loss) on Securities [Line Items]
Equity securities, FV-NI, gain (loss)	24,000,000
Preferred stock
Gain (Loss) on Securities [Line Items]
Equity securities, FV-NI, gain (loss)	$ 73,000,000

Investments (Net realized inves

Investments (Net realized investment gains (losses)) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Fixed maturity securities:
Gross realized gains	$ 168	$ 186	$ 204
Gross realized losses	(164)	(64)	(138)
Net realized investment gains (losses) on fixed maturity securities	4	122	66
Equity securities	(74)
Derivatives	9	(4)	(2)
Short term investments and other	9	(25)	(9)
Net realized investment gains (losses)	$ (52)	93	50
Equity securities
Fixed maturity securities:
Equity securities		$ 0	$ (5)

Investments (Net change in unre

Investments (Net change in unrealized gains (losses) on investments) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Debt Securities, Available-for-sale [Line Items]
Total net change in unrealized gains on investments	$ (1,811)	$ 758	$ 224
Fixed maturity securities
Debt Securities, Available-for-sale [Line Items]
Total net change in unrealized gains on investments	(1,811)	728	225
Equity securities
Debt Securities, Available-for-sale [Line Items]
Total net change in unrealized gains on investments	0	32	(2)
Other
Debt Securities, Available-for-sale [Line Items]
Total net change in unrealized gains on investments	$ 0	$ (2)	$ 1

Investments (Components of othe

Investments (Components of other-than-temporary impairment losses recognized in earnings) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Debt Securities, Available-for-sale [Line Items]
Total fixed maturity securities available-for-sale	$ 21	$ 13	$ 72
OTTI losses recognized in earnings	21	14	81
Corporate and other bonds
Debt Securities, Available-for-sale [Line Items]
Total fixed maturity securities available-for-sale	12	12	59
Asset-backed
Debt Securities, Available-for-sale [Line Items]
Total fixed maturity securities available-for-sale	9	1	13
Equity securities
Debt Securities, Available-for-sale [Line Items]
OTTI losses recognized in earnings	$ 0	$ 1	$ 9

Investments (Summary of fixed m

Investments (Summary of fixed maturity and equity securities) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	$ 38,081	$ 38,212
Gross Unrealized Gains	1,982
Gross Unrealized Losses	521
Estimated Fair Value	39,542	41,484
Total fixed maturity securities trading
Estimated fair value, trading securities	39,546	41,487
Equity securities available-for-sale:
Cost or Amortized Cost		659
Estimated Fair Value		695
Debt securities, amortized cost	38,085
Debt securities	39,546	41,487
Marketable securities, amortized cost		38,874
Gross Unrealized Gains		3,397
Gross Unrealized Losses		89
Marketable securities		42,182
Corporate and other bonds
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	18,764	17,210
Gross Unrealized Gains	791	1,625
Gross Unrealized Losses	395	28
Estimated Fair Value	19,160	18,807
Equity securities available-for-sale:
Debt securities	19,814	19,374
Unrealized OTTI Losses (Gains)	0	0
States, municipalities and political subdivisions
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	9,681	12,478
Gross Unrealized Gains	1,076	1,551
Gross Unrealized Losses	9	2
Estimated Fair Value	10,748	14,027
Equity securities available-for-sale:
Debt securities	10,748	14,027
Unrealized OTTI Losses (Gains)	0	(11)
Residential mortgage-backed
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	4,815	5,043
Gross Unrealized Gains	68	109
Gross Unrealized Losses	57	32
Estimated Fair Value	4,826	5,120
Equity securities available-for-sale:
Unrealized OTTI Losses (Gains)	(20)	(27)
Commercial mortgage-backed
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	2,200	1,840
Gross Unrealized Gains	28	46
Gross Unrealized Losses	32	14
Estimated Fair Value	2,196	1,872
Equity securities available-for-sale:
Unrealized OTTI Losses (Gains)	0	0
Other asset-backed
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	1,975	1,083
Gross Unrealized Gains	11	16
Gross Unrealized Losses	24	5
Estimated Fair Value	1,962	1,094
Equity securities available-for-sale:
Unrealized OTTI Losses (Gains)	0	0
Asset-backed
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	8,990	7,966
Gross Unrealized Gains	107	171
Gross Unrealized Losses	113	51
Estimated Fair Value	8,984	8,086
Equity securities available-for-sale:
Debt securities	8,984	8,086
Unrealized OTTI Losses (Gains)	(20)	(27)
U.S. Treasury and obligations of government-sponsored enterprises
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	156	111
Gross Unrealized Gains	3	2
Gross Unrealized Losses	0	4
Estimated Fair Value	159	109
Equity securities available-for-sale:
Unrealized OTTI Losses (Gains)	0	0
Foreign government
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	480	437
Gross Unrealized Gains	5	9
Gross Unrealized Losses	4	2
Estimated Fair Value	481	444
Equity securities available-for-sale:
Unrealized OTTI Losses (Gains)	0	0
Redeemable preferred stock
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	10	10
Gross Unrealized Gains	0	1
Gross Unrealized Losses	0	0
Estimated Fair Value	10	11
Equity securities available-for-sale:
Unrealized OTTI Losses (Gains)	0	0
Fixed maturity securities
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	38,081	38,212
Gross Unrealized Gains	1,982	3,359
Gross Unrealized Losses	521	87
Estimated Fair Value	39,542	41,484
Equity securities available-for-sale:
Unrealized OTTI Losses (Gains)	(20)	(38)
Total fixed maturity securities trading
Total fixed maturity securities trading
Cost or amortized cost, trading securities	4	3
Gross unrealized gains, trading securities	0	0
Gross unrealized losses, trading securities	0	0
Estimated fair value, trading securities	$ 4	3
Common Stock
Equity securities available-for-sale:
Cost or Amortized Cost		21
Gross Unrealized Gains		7
Gross Unrealized Losses		1
Estimated Fair Value		27
Preferred stock
Equity securities available-for-sale:
Cost or Amortized Cost		638
Gross Unrealized Gains		31
Gross Unrealized Losses		1
Estimated Fair Value		668
Equity securities
Equity securities available-for-sale:
Cost or Amortized Cost		659
Gross Unrealized Gains		38
Gross Unrealized Losses		2
Estimated Fair Value		$ 695

Investments (Securities in a gr

Investments (Securities in a gross unrealized loss position) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	$ 12,689
Estimated Fair Value, Less than 12 Months		$ 3,620
Gross Unrealized Losses, Less than 12 Months	404
Gross Unrealized Losses, Less than 12 Months		40
Estimated Fair Value, 12 Months or Longer	2,614
Estimated Fair Value, 12 Months or Longer		1,455
Gross Unrealized Losses, 12 Months or Longer	117
Gross Unrealized Losses, 12 Months or Longer		49
Estimated Fair Value, Total	15,303
Estimated Fair Value, Total		5,075
Gross Unrealized Losses, Total	521
Gross Unrealized Losses, Total		89
Corporate and other bonds
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	8,543
Estimated Fair Value, Less than 12 Months		1,354
Gross Unrealized Losses, Less than 12 Months	340
Gross Unrealized Losses, Less than 12 Months		21
Estimated Fair Value, 12 Months or Longer	825
Estimated Fair Value, 12 Months or Longer		168
Gross Unrealized Losses, 12 Months or Longer	55
Gross Unrealized Losses, 12 Months or Longer		7
Estimated Fair Value, Total	9,368
Estimated Fair Value, Total		1,522
Gross Unrealized Losses, Total	395
Gross Unrealized Losses, Total		28
States, municipalities and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	517
Estimated Fair Value, Less than 12 Months		72
Gross Unrealized Losses, Less than 12 Months	8
Gross Unrealized Losses, Less than 12 Months		1
Estimated Fair Value, 12 Months or Longer	5
Estimated Fair Value, 12 Months or Longer		85
Gross Unrealized Losses, 12 Months or Longer	1
Gross Unrealized Losses, 12 Months or Longer		1
Estimated Fair Value, Total	522
Estimated Fair Value, Total		157
Gross Unrealized Losses, Total	9
Gross Unrealized Losses, Total		2
Residential mortgage-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	1,932
Estimated Fair Value, Less than 12 Months		1,228
Gross Unrealized Losses, Less than 12 Months	23
Gross Unrealized Losses, Less than 12 Months		5
Estimated Fair Value, 12 Months or Longer	1,119
Estimated Fair Value, 12 Months or Longer		947
Gross Unrealized Losses, 12 Months or Longer	34
Gross Unrealized Losses, 12 Months or Longer		27
Estimated Fair Value, Total	3,051
Estimated Fair Value, Total		2,175
Gross Unrealized Losses, Total	57
Gross Unrealized Losses, Total		32
Commercial mortgage-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	728
Estimated Fair Value, Less than 12 Months		403
Gross Unrealized Losses, Less than 12 Months	10
Gross Unrealized Losses, Less than 12 Months		4
Estimated Fair Value, 12 Months or Longer	397
Estimated Fair Value, 12 Months or Longer		212
Gross Unrealized Losses, 12 Months or Longer	22
Gross Unrealized Losses, 12 Months or Longer		10
Estimated Fair Value, Total	1,125
Estimated Fair Value, Total		615
Gross Unrealized Losses, Total	32
Gross Unrealized Losses, Total		14
Other asset-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	834
Estimated Fair Value, Less than 12 Months		248
Gross Unrealized Losses, Less than 12 Months	21
Gross Unrealized Losses, Less than 12 Months		3
Estimated Fair Value, 12 Months or Longer	125
Estimated Fair Value, 12 Months or Longer		18
Gross Unrealized Losses, 12 Months or Longer	3
Gross Unrealized Losses, 12 Months or Longer		2
Estimated Fair Value, Total	959
Estimated Fair Value, Total		266
Gross Unrealized Losses, Total	24
Gross Unrealized Losses, Total		5
Asset-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	3,494
Estimated Fair Value, Less than 12 Months		1,879
Gross Unrealized Losses, Less than 12 Months	54
Gross Unrealized Losses, Less than 12 Months		12
Estimated Fair Value, 12 Months or Longer	1,641
Estimated Fair Value, 12 Months or Longer		1,177
Gross Unrealized Losses, 12 Months or Longer	59
Gross Unrealized Losses, 12 Months or Longer		39
Estimated Fair Value, Total	5,135
Estimated Fair Value, Total		3,056
Gross Unrealized Losses, Total	113
Gross Unrealized Losses, Total		51
U.S. Treasury and obligations of government-sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	21
Estimated Fair Value, Less than 12 Months		49
Gross Unrealized Losses, Less than 12 Months	0
Gross Unrealized Losses, Less than 12 Months		2
Estimated Fair Value, 12 Months or Longer	19
Estimated Fair Value, 12 Months or Longer		21
Gross Unrealized Losses, 12 Months or Longer	0
Gross Unrealized Losses, 12 Months or Longer		2
Estimated Fair Value, Total	40
Estimated Fair Value, Total		70
Gross Unrealized Losses, Total	0
Gross Unrealized Losses, Total		4
Foreign government
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	114
Estimated Fair Value, Less than 12 Months		166
Gross Unrealized Losses, Less than 12 Months	2
Gross Unrealized Losses, Less than 12 Months		2
Estimated Fair Value, 12 Months or Longer	124
Estimated Fair Value, 12 Months or Longer		4
Gross Unrealized Losses, 12 Months or Longer	2
Gross Unrealized Losses, 12 Months or Longer		0
Estimated Fair Value, Total	238
Estimated Fair Value, Total		170
Gross Unrealized Losses, Total	$ 4
Gross Unrealized Losses, Total		2
Fixed maturity securities
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 Months		3,520
Gross Unrealized Losses, Less than 12 Months		38
Estimated Fair Value, 12 Months or Longer		1,455
Gross Unrealized Losses, 12 Months or Longer		49
Estimated Fair Value, Total		4,975
Gross Unrealized Losses, Total		87
Common Stock
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 Months		7
Gross Unrealized Losses, Less than 12 Months		1
Estimated Fair Value, 12 Months or Longer		0
Gross Unrealized Losses, 12 Months or Longer		0
Estimated Fair Value, Total		7
Gross Unrealized Losses, Total		1
Preferred stock
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 Months		93
Gross Unrealized Losses, Less than 12 Months		1
Estimated Fair Value, 12 Months or Longer		0
Gross Unrealized Losses, 12 Months or Longer		0
Estimated Fair Value, Total		93
Gross Unrealized Losses, Total		1
Equity securities
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 Months		100
Gross Unrealized Losses, Less than 12 Months		2
Estimated Fair Value, 12 Months or Longer		0
Gross Unrealized Losses, 12 Months or Longer		0
Estimated Fair Value, Total		100
Gross Unrealized Losses, Total		$ 2

Investments (Activity related t

Investments (Activity related to the pretax fixed maturity credit loss component reflected within retained earnings for securities still held for which a portion of an OTTI loss was recognized in OCI) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Balance beginning of period	$ 27	$ 36	$ 53
Reductions for securities sold during the period	(9)	(9)	(16)
Reductions for securities the Company intends to sell or more likely than not will be required to sell	0	0	(1)
Balance end of period	$ 18	$ 27	$ 36

Investments (Contractual maturi

Investments (Contractual maturity) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Investments [Abstract]
Due in one year or less, cost or amortized cost	$ 1,350	$ 1,135
Due after one year through five years, cost or amortized cost	7,979	8,165
Due after five years through ten years, cost or amortized cost	16,859	16,060
Due after ten years, cost or amortized cost	11,893	12,852
Cost or Amortized Cost	38,081	38,212
Due in one year or less, estimated fair value	1,359	1,157
Due after one year through five years, estimated fair value	8,139	8,501
Due after five years through ten years, estimated fair value	16,870	16,718
Due after ten years, estimated fair value	13,174	15,108
Total Estimated Fair Value	$ 39,542	$ 41,484

Fair Value (Assets and liabilit

Fair Value (Assets and liabilities measured at fair value on a recurring basis) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Fixed maturity securities:
Debt securities	$ 39,546	$ 41,487
Equity securities:
Equity securities	780	695
Estimated Fair Value		695
Short term and other	1,165	1,354
Total assets	41,491	43,536
Other liabilities	(4)	3
Total liabilities	(4)	3
Corporate and other bonds
Fixed maturity securities:
Debt securities	19,814	19,374
States, municipalities and political subdivisions
Fixed maturity securities:
Debt securities	10,748	14,027
Asset-backed
Fixed maturity securities:
Debt securities	8,984	8,086
Common Stock
Equity securities:
Equity securities	148
Estimated Fair Value		27
Preferred stock
Equity securities:
Equity securities	632
Estimated Fair Value		668
Level 1
Fixed maturity securities:
Debt securities	196	128
Equity securities:
Equity securities	192
Estimated Fair Value		91
Short term and other	216	396
Total assets	604	615
Other liabilities	0	0
Total liabilities	0	0
Level 1 | Corporate and other bonds
Fixed maturity securities:
Debt securities	196	128
Level 1 | States, municipalities and political subdivisions
Fixed maturity securities:
Debt securities	0	0
Level 1 | Asset-backed
Fixed maturity securities:
Debt securities	0	0
Level 1 | Common Stock
Equity securities:
Equity securities	144
Estimated Fair Value		23
Level 1 | Preferred stock
Equity securities:
Equity securities	48
Estimated Fair Value		68
Level 2
Fixed maturity securities:
Debt securities	38,931	40,925
Equity securities:
Equity securities	570
Estimated Fair Value		584
Short term and other	949	958
Total assets	40,450	42,467
Other liabilities	(4)	3
Total liabilities	(4)	3
Level 2 | Corporate and other bonds
Fixed maturity securities:
Debt securities	19,396	19,148
Level 2 | States, municipalities and political subdivisions
Fixed maturity securities:
Debt securities	10,748	14,026
Level 2 | Asset-backed
Fixed maturity securities:
Debt securities	8,787	7,751
Level 2 | Common Stock
Equity securities:
Equity securities	0
Estimated Fair Value		0
Level 2 | Preferred stock
Equity securities:
Equity securities	570
Estimated Fair Value		584
Level 3
Fixed maturity securities:
Debt securities	419	434
Equity securities:
Equity securities	18
Estimated Fair Value		20
Short term and other	0	0
Total assets	437	454
Other liabilities	0	0
Total liabilities	0	0
Level 3 | Corporate and other bonds
Fixed maturity securities:
Debt securities	222	98
Level 3 | States, municipalities and political subdivisions
Fixed maturity securities:
Debt securities	0	1
Level 3 | Asset-backed
Fixed maturity securities:
Debt securities	197	335
Level 3 | Common Stock
Equity securities:
Equity securities	4
Estimated Fair Value		4
Level 3 | Preferred stock
Equity securities:
Equity securities	$ 14
Estimated Fair Value		$ 16

Fair Value (Table of reconcilia

Fair Value (Table of reconciliation for assets and liabilities measured at fair value on a recurring basis using significant unobservable inputs) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	$ 454	$ 407
Reported in Net investment income	0
Total realized and unrealized investment gains (losses)	(12)	9
Total realized and unrealized investment gains (losses)	(10)	18
Purchases	279	126
Sales	(77)	(68)
Settlements	(74)	(102)
Transfers into Level 3	77	169
Transfers out of Level 3	(212)	(96)
Balance, Ending, Assets	437	454
Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2018 recognized in Net income (loss)	(4)
Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2018 recognized in Other comprehensive income (loss)	(9)
Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2017 recognized in Net income (loss)		0
Corporate and other bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	98	130
Reported in Net investment income	0
Total realized and unrealized investment gains (losses)	(4)	3
Total realized and unrealized investment gains (losses)	(5)	3
Purchases	117	18
Sales	(5)	(5)
Settlements	(9)	(54)
Transfers into Level 3	35	16
Transfers out of Level 3	(9)	(10)
Balance, Ending, Assets	222	98
Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2018 recognized in Net income (loss)	0
Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2018 recognized in Other comprehensive income (loss)	(5)
Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2017 recognized in Net income (loss)		0
States, municipalities and political subdivisions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	1	1
Reported in Net investment income	0
Total realized and unrealized investment gains (losses)	0	0
Total realized and unrealized investment gains (losses)	0	0
Purchases	0	0
Sales	0	0
Settlements	(1)	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Balance, Ending, Assets	0	1
Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2018 recognized in Net income (loss)	0
Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2018 recognized in Other comprehensive income (loss)	0
Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2017 recognized in Net income (loss)		0
Asset-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	335	199
Reported in Net investment income	0
Total realized and unrealized investment gains (losses)	(8)	3
Total realized and unrealized investment gains (losses)	(3)	5
Purchases	162	107
Sales	(72)	0
Settlements	(64)	(43)
Transfers into Level 3	42	153
Transfers out of Level 3	(203)	(86)
Balance, Ending, Assets	197	335
Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2018 recognized in Net income (loss)	(2)
Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2018 recognized in Other comprehensive income (loss)	(4)
Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2017 recognized in Net income (loss)		0
Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	20	19
Reported in Net investment income	0
Total realized and unrealized investment gains (losses)	0	3
Total realized and unrealized investment gains (losses)	(2)	3
Purchases	0	1
Sales	0	(3)
Settlements	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Balance, Ending, Assets	18	20
Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2018 recognized in Net income (loss)	(2)
Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2018 recognized in Other comprehensive income (loss)	0
Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2017 recognized in Net income (loss)		0
Derivative financial instruments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	0	0
Reported in Net investment income	0
Total realized and unrealized investment gains (losses)	0	0
Total realized and unrealized investment gains (losses)	0	1
Purchases	0	0
Sales	0	(1)
Settlements	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Balance, Ending, Assets	0	0
Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2018 recognized in Net income (loss)	0
Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2018 recognized in Other comprehensive income (loss)	0
Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2017 recognized in Net income (loss)		0
Life settlement contracts, included in Other assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	0	58
Total realized and unrealized investment gains (losses)		0
Total realized and unrealized investment gains (losses)		6
Purchases		0
Sales		(59)
Settlements		(5)
Transfers into Level 3		0
Transfers out of Level 3		0
Balance, Ending, Assets		0
Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2017 recognized in Net income (loss)		0
Reported in Net realized investment gains (losses)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Other comprehensive income (loss)	2	3
Reported in Net realized investment gains (losses) | Corporate and other bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Other comprehensive income (loss)	(1)	0
Reported in Net realized investment gains (losses) | States, municipalities and political subdivisions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Other comprehensive income (loss)	0	0
Reported in Net realized investment gains (losses) | Asset-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Other comprehensive income (loss)	5	2
Reported in Net realized investment gains (losses) | Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Other comprehensive income (loss)	(2)	0
Reported in Net realized investment gains (losses) | Derivative financial instruments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Other comprehensive income (loss)	$ 0	1
Reported in Net realized investment gains (losses) | Life settlement contracts, included in Other assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Other comprehensive income (loss)		0
Reported in Other revenues
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Other comprehensive income (loss)		6
Reported in Other revenues | Corporate and other bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Other comprehensive income (loss)		0
Reported in Other revenues | States, municipalities and political subdivisions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Other comprehensive income (loss)		0
Reported in Other revenues | Asset-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Other comprehensive income (loss)		0
Reported in Other revenues | Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Other comprehensive income (loss)		0
Reported in Other revenues | Derivative financial instruments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Other comprehensive income (loss)		0
Reported in Other revenues | Life settlement contracts, included in Other assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Other comprehensive income (loss)		$ 6

Fair Value (Narrative) (Details

Fair Value (Narrative) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Other invested assets overseas deposit	$ 48	$ 39

Fair Value (Quantitative inform

Fair Value (Quantitative information about significant unobservable inputs in the fair value measurement of level 3 assets) (Details) $ in Millions	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Estimated fair value	$ 41,491	$ 43,536
Fixed maturity securities | Income Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Estimated fair value	$ 228	$ 136
Measurement Input, Credit Spread | Income Approach Valuation Technique | Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Debt securities, available-for-sale, measurement Input	0.01	0.01
Measurement Input, Credit Spread | Income Approach Valuation Technique | Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Debt securities, available-for-sale, measurement Input	0.12	0.12
Measurement Input, Credit Spread | Income Approach Valuation Technique | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Debt securities, available-for-sale, measurement Input	0.03	0.03

Fair Value (Carrying amount and

Fair Value (Carrying amount and estimated fair value of financial instrument assets and liabilities which are not measured at fair value) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Financial Assets [Abstract]
Mortgage loans	$ 839	$ 839
Financial Liabilities [Abstract]
Short term debt	0	150
Long term debt	2,680	2,708
Carrying Amount
Financial Assets [Abstract]
Mortgage loans	839	839
Note receivable	35	46
Financial Liabilities [Abstract]
Short term debt		150
Long term debt	2,680	2,708
Estimated Fair Value
Financial Assets [Abstract]
Mortgage loans	827	844
Note receivable	35	46
Financial Liabilities [Abstract]
Short term debt		150
Long term debt	2,731	2,896
Level 1 | Estimated Fair Value
Financial Assets [Abstract]
Mortgage loans	0	0
Note receivable	0	0
Financial Liabilities [Abstract]
Short term debt		0
Long term debt	0	0
Level 2 | Estimated Fair Value
Financial Assets [Abstract]
Mortgage loans	0	0
Note receivable	0	0
Financial Liabilities [Abstract]
Short term debt		150
Long term debt	2,731	2,896
Level 3 | Estimated Fair Value
Financial Assets [Abstract]
Mortgage loans	827	844
Note receivable	35	46
Financial Liabilities [Abstract]
Short term debt		0
Long term debt	$ 0	$ 0

Income Taxes (Narrative) (Detai

Income Taxes (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Contingency [Line Items]
Unrecognized tax benefits	$ 0	$ 0
Interest income (expense)	0	0	$ 0
Income tax penalties expense	0	0	0
Accrued interest and penalties	0	0
Net deferred tax asset remeasurement	(6,000,000)	83,000,000
Net deferred tax asset remeasurement	6,000,000	(83,000,000)	0
Deferred tax liability on undistributed income related to a foreign subsidiary	0
Foreign tax expense (benefit) on income from continuing operations	(5,000,000)	1,000,000	(9,000,000)
Income (loss) from continuing foreign operations	22,000,000	39,000,000	51,000,000
Operating loss carryforwards	0
Valuation allowance	0	0
Federal Income Taxes
Income Tax Contingency [Line Items]
Related party transaction, amounts of transaction	$ 275,000,000	$ 127,000,000	$ 142,000,000

Income Taxes (Reconciliation be

Income Taxes (Reconciliation between the Company's federal income tax (expense) benefit at statutory rates and the recorded income tax (expense) benefit) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Income tax expense at statutory rates	$ (203)	$ (459)	$ (398)
Tax benefit from tax exempt income	63	131	124
Foreign taxes and credits	(1)	3	3
State income taxes	(13)	(7)	(6)
Net deferred tax asset remeasurement	6	(83)	0
Other tax expense	(3)	4	(1)
Income tax expense	$ (151)	$ (411)	$ (278)

Income Taxes (Current and defer

Income Taxes (Current and deferred components of the Company's income tax (expense) benefit) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Current tax expense	$ (171)	$ (243)	$ (142)
Deferred tax benefit (expense)	20	(168)	(136)
Income tax expense	$ (151)	$ (411)	$ (278)

Income Taxes (Significant compo

Income Taxes (Significant components of the Company's deferred tax assets and liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Deferred Tax Assets:
Property and casualty claim and claim adjustment expense reserves	$ 108		$ 74
Unearned premium reserves	108		142
Receivables	15		15
Employee benefits	143		154
Deferred retroactive reinsurance benefit	79		68
Other assets	131		105
Gross deferred tax assets	584		558
Deferred Tax Liabilities:
Investment valuation differences	44		55
Deferred acquisition costs	78		77
Net unrealized gains	14		233
Software and hardware	44		46
Other liabilities	12		10
Gross deferred tax liabilities	192		421
Net deferred tax asset	$ 392	$ 158	$ 137

Claim and Claim Adjustment Ex_3

Claim and Claim Adjustment Expense Reserves (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2010
Liability for Claims and Claims Adjustment Expense [Line Items]
Pretax (favorable) unfavorable net prior year claim and allocated claim adjustment expense reserve development Life & Group	$ (19)	$ (72)	$ (46)
Asbestos and Environmental Reserves
Liability for Claims and Claims Adjustment Expense [Line Items]
Net A&EP claim and allocated claim adjustment expense reserves ceded to NICO				$ 1,600
Aggregate limit under A&EP Loss Portfolio Transfer				4,000
A&EP claim and allocated claim adjustment expense reserves ceded under existing third party reinsurance contracts transferred to NICO under A&EP Loss Portfolio Transfer				1,200
Reinsurance premium paid to NICO under A&EP Loss Portfolio Transfer				2,000
Net reinsurance receivables transferrred to NICO under A&EP Loss Portfolio Transfer				215
Total consideration paid to NICO under AEP Loss Portfolio Transfer				$ 2,200
Net A&EP adverse development before consideration of LPT	178	60	$ 200
Cumulative amounts ceded under AEP Loss Portfolio Transfer	3,100	2,900
Deferred reinsurance benefit yet to be recognized	374	326
Fair value of collateral trust account established by NICO under A&EP Loss Portfolio Transfer	$ 2,700	$ 3,100

Claim and Claim Adjustment Ex_4

Claim and Claim Adjustment Expense Reserves (Reconciliation of Liability for Unpaid Claim and Claim Adjustment Expense) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Liability for Claims and Claims Adjustment Expense [Line Items]
Total net liability for unpaid claim and claim adjustment expenses	$ 17,965	$ 18,070	$ 18,249	$ 18,576
Reinsurance receivables	4,019
Claim and claim adjustment expenses	21,984	22,004
Specialty
Liability for Claims and Claims Adjustment Expense [Line Items]
Total net liability for unpaid claim and claim adjustment expenses	4,831	5,007
Reinsurance receivables	634
Commercial
Liability for Claims and Claims Adjustment Expense [Line Items]
Total net liability for unpaid claim and claim adjustment expenses	7,998	8,136
Reinsurance receivables	745
International
Liability for Claims and Claims Adjustment Expense [Line Items]
Total net liability for unpaid claim and claim adjustment expenses	1,524	1,432
Reinsurance receivables	226
Corporate & Other
Liability for Claims and Claims Adjustment Expense [Line Items]
Total net liability for unpaid claim and claim adjustment expenses	192	$ 205
Reinsurance receivables	2,233
Life and Group
Liability for Claims and Claims Adjustment Expense [Line Items]
Total net liability for unpaid claim and claim adjustment expenses	3,420
Reinsurance receivables	$ 181

Claim and Claim Adjustment Ex_5

Claim and Claim Adjustment Expense Reserves (Reconciliation of claim and claim adjustment expense reserves) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reserves, beginning of year: [Abstract]
Gross	$ 22,004	$ 22,343	$ 22,663
Ceded	3,934	4,094	4,087
Net reserves, beginning of year	18,070	18,249	18,576
Net incurred claim and claim adjustment expenses:
Provision for insured events of current year	5,358	5,201	5,025
Decrease in provision for insured events of prior years	(179)	(381)	(342)
Amortization of discount	176	179	175
Total net incurred	5,355	4,999	4,858
Net payments attributable to:
Current year events	(1,046)	(975)	(967)
Prior year events	(4,285)	(4,366)	(4,167)
Total net payments	(5,331)	(5,341)	(5,134)
Foreign currency translation adjustment and other	(129)	163	(51)
Net reserves, end of year	17,965	18,070	18,249
Ceded reserves, end of year	4,019	3,934	4,094
Gross reserves, end of year	$ 21,984	$ 22,004	$ 22,343

Claim and Claim Adjustment Ex_6

Claim and Claim Adjustment Expense Reserves (Gross and net carried claim and claim adjustment expense reserves) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Liability for Claims and Claims Adjustment Expense [Line Items]
Gross Case Reserves	$ 11,395	$ 11,670
Gross IBNR Reserves	10,589	10,334
Total Gross Carried Claim and Claim Adjustment Expense Reserves	21,984	22,004	$ 22,343	$ 22,663
Net Case Reserves	9,523	9,645
Net IBNR Reserves	8,442	8,425
Total Net Carried Claim and Claim Adjustment Expense Reserves	17,965	18,070	$ 18,249	$ 18,576
Specialty
Liability for Claims and Claims Adjustment Expense [Line Items]
Gross Case Reserves	1,623	1,742
Gross IBNR Reserves	3,842	3,927
Total Gross Carried Claim and Claim Adjustment Expense Reserves	5,465	5,669
Net Case Reserves	1,483	1,600
Net IBNR Reserves	3,348	3,407
Total Net Carried Claim and Claim Adjustment Expense Reserves	4,831	5,007
Commercial
Liability for Claims and Claims Adjustment Expense [Line Items]
Gross Case Reserves	4,181	4,427
Gross IBNR Reserves	4,562	4,337
Total Gross Carried Claim and Claim Adjustment Expense Reserves	8,743	8,764
Net Case Reserves	3,831	4,103
Net IBNR Reserves	4,167	4,033
Total Net Carried Claim and Claim Adjustment Expense Reserves	7,998	8,136
International
Liability for Claims and Claims Adjustment Expense [Line Items]
Gross Case Reserves	867	744
Gross IBNR Reserves	883	892
Total Gross Carried Claim and Claim Adjustment Expense Reserves	1,750	1,636
Net Case Reserves	749	640
Net IBNR Reserves	775	792
Total Net Carried Claim and Claim Adjustment Expense Reserves	1,524	1,432
Life & Group
Liability for Claims and Claims Adjustment Expense [Line Items]
Gross Case Reserves	3,516	3,386
Gross IBNR Reserves	85	113
Total Gross Carried Claim and Claim Adjustment Expense Reserves	3,601	3,499
Net Case Reserves	3,364	3,208
Net IBNR Reserves	56	82
Total Net Carried Claim and Claim Adjustment Expense Reserves	3,420	3,290
Corporate & Other
Liability for Claims and Claims Adjustment Expense [Line Items]
Gross Case Reserves	1,208	1,371
Gross IBNR Reserves	1,217	1,065
Total Gross Carried Claim and Claim Adjustment Expense Reserves	2,425	2,436
Net Case Reserves	96	94
Net IBNR Reserves	96	111
Total Net Carried Claim and Claim Adjustment Expense Reserves	$ 192	$ 205

Claim and Claim Adjustment Ex_7

Claim and Claim Adjustment Expense Reserves (Net prior year development) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Pretax (favorable) unfavorable premium development, excluding Life & Group	$ (181)	$ (308)	$ (288)
Specialty
Segment Reporting Information [Line Items]
Pretax (favorable) unfavorable premium development, excluding Life & Group	(150)	(174)	(247)
Commercial
Segment Reporting Information [Line Items]
Pretax (favorable) unfavorable premium development, excluding Life & Group	(25)	(115)	15
International
Segment Reporting Information [Line Items]
Pretax (favorable) unfavorable premium development, excluding Life & Group	(4)	(9)	(58)
Corporate & Other
Segment Reporting Information [Line Items]
Pretax (favorable) unfavorable premium development, excluding Life & Group	$ (2)	$ (10)	$ 2

Claim and Claim Adjustment Ex_8

Claim and Claim Adjustment Expense Reserves (Specialty - Net prior year claim and allocated claim adjustment expense reserve development) (Details) - Specialty - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Liability for Claims and Claims Adjustment Expense [Line Items]
Medical Professional Liability	$ 47	$ 30	$ 9
Other Professional Liability and Management Liability	(127)	(126)	(140)
Surety	(70)	(84)	(63)
Warranty	(10)	4	4
Other	10	2	(57)
Total pretax (favorable) unfavorable development	$ (150)	$ (174)	$ (247)

Claim and Claim Adjustment Ex_9

Claim and Claim Adjustment Expense Reserves (Specialty - Line of Business Composition) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total net liability for unpaid claim and claim adjustment expenses	$ 17,965	$ 18,070	$ 18,249	$ 18,576
Specialty
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total net liability for unpaid claim and claim adjustment expenses	4,831	$ 5,007
Medical Professional Liability | Specialty
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total net liability for unpaid claim and claim adjustment expenses	1,457
Other Professional Liability and Management Liability | Specialty
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total net liability for unpaid claim and claim adjustment expenses	2,849
Surety | Specialty
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total net liability for unpaid claim and claim adjustment expenses	379
Warranty | Specialty
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total net liability for unpaid claim and claim adjustment expenses	40
Other | Specialty
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total net liability for unpaid claim and claim adjustment expenses	$ 106

Claim and Claim Adjustment E_10

Claim and Claim Adjustment Expense Reserves (Specialty - Medical Professional Liability - Cumulative Net Incurred Claims and Allocated Claim Adjustment Expenses) (Details) - Medical Professional Liability - Specialty $ in Millions	Dec. 31, 2018USD ($)claims	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)	Dec. 31, 2012USD ($)	Dec. 31, 2011USD ($)	Dec. 31, 2010USD ($)	Dec. 31, 2009USD ($)
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 4,498
IBNR	824
2,009
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	310	$ 302	$ 309	$ 336	$ 346	$ 366	$ 392	$ 392	$ 390	$ 389
IBNR	$ 0
Cumulative Number of Claims | claims	14,716
2,010
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 356	360	365	395	415	426	423	412	$ 402
IBNR	$ 0
Cumulative Number of Claims | claims	14,615
2,011
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 437	437	434	439	468	443	437	$ 429
IBNR	$ 8
Cumulative Number of Claims | claims	16,505
2,012
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 493	484	493	498	508	469	$ 464
IBNR	$ 10
Cumulative Number of Claims | claims	17,691
2,013
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 535	525	513	500	479	$ 462
IBNR	$ 28
Cumulative Number of Claims | claims	19,442
2,014
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 535	530	537	489	$ 450
IBNR	$ 30
Cumulative Number of Claims | claims	19,602
2,015
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 494	510	499	$ 433
IBNR	$ 78
Cumulative Number of Claims | claims	17,835
2,016
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 485	487	$ 427
IBNR	$ 120
Cumulative Number of Claims | claims	15,427
2,017
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 449	$ 412
IBNR	$ 217
Cumulative Number of Claims | claims	13,777
2,018
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 404
IBNR	$ 333
Cumulative Number of Claims | claims	11,205

Claim and Claim Adjustment E_11

Claim and Claim Adjustment Expense Reserves (Specialty - Medical Professional Liability - Net Cumulative Paid Claim and Claim Adjustment Expenses) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Net liability for unpaid claim and claim adjustment expenses for accident years prior to 2009	$ 4,285	$ 4,366	$ 4,167
Total net liability for unpaid claim and claim adjustment expenses	17,965	18,070	18,249	$ 18,576
Specialty
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Total net liability for unpaid claim and claim adjustment expenses	4,831	5,007
Medical Professional Liability | Specialty
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	3,082
Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented	1,416
Net liability for unpaid claim and claim adjustment expenses for accident years prior to 2009	18
Liability for unallocated claim adjustment expenses for accident years presented	23
Total net liability for unpaid claim and claim adjustment expenses	1,457
Medical Professional Liability | 2009 | Specialty
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	300	291	288	280	$ 269	$ 247	$ 211	$ 143	$ 63	$ 9
Medical Professional Liability | 2010 | Specialty
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	350	346	337	326	306	257	173	86	$ 10
Medical Professional Liability | 2011 | Specialty
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	409	398	375	347	295	208	109	$ 17
Medical Professional Liability | 2012 | Specialty
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	457	427	388	323	221	117	$ 14
Medical Professional Liability | 2013 | Specialty
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	462	414	355	255	119	$ 17
Medical Professional Liability | 2014 | Specialty
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	417	359	258	136	$ 23
Medical Professional Liability | 2015 | Specialty
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	313	230	101	$ 22
Medical Professional Liability | 2016 | Specialty
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	246	121	$ 18
Medical Professional Liability | 2017 | Specialty
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	107	$ 19
Medical Professional Liability | 2018 | Specialty
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	$ 21

Claim and Claim Adjustment E_12

Claim and Claim Adjustment Expense Reserves (Specialty - Medical Professional Liability - Net Strengthening or Releasing of Prior Accident Year Reserves) (Details) - Specialty - USD ($) $ in Millions	12 Months Ended									24 Months Ended	36 Months Ended	48 Months Ended	60 Months Ended	72 Months Ended	84 Months Ended	96 Months Ended	108 Months Ended	120 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018
Claims Development [Line Items]
Total	$ 47	$ 30	$ 9
Medical Professional Liability
Claims Development [Line Items]
Cumulative Number of Claims	47	58	60
Total net development for accident years prior to 2009	1	(21)	(51)
Total unallocated claim adjustment expense development	(1)	(7)	0
Total	47	30	9
Medical Professional Liability | 2009
Claims Development [Line Items]
Cumulative Number of Claims	8	(7)	(27)	$ (10)	$ (20)	$ (26)	$ 0	$ 2	$ 1									$ (79)
Medical Professional Liability | 2010
Claims Development [Line Items]
Cumulative Number of Claims	(4)	(5)	(30)	(20)	(11)	3	11	$ 10									$ (46)
Medical Professional Liability | 2011
Claims Development [Line Items]
Cumulative Number of Claims	0	3	(5)	(29)	25	6	$ 8									$ 8
Medical Professional Liability | 2012
Claims Development [Line Items]
Cumulative Number of Claims	9	(9)	(5)	(10)	39	$ 5									$ 29
Medical Professional Liability | 2013
Claims Development [Line Items]
Cumulative Number of Claims	10	12	13	21	$ 17									$ 73
Medical Professional Liability | 2014
Claims Development [Line Items]
Cumulative Number of Claims	5	(7)	48	$ 39									$ 85
Medical Professional Liability | 2015
Claims Development [Line Items]
Cumulative Number of Claims	(16)	11	$ 66									$ 61
Medical Professional Liability | 2016
Claims Development [Line Items]
Cumulative Number of Claims	(2)	$ 60									$ 58
Medical Professional Liability | 2017
Claims Development [Line Items]
Cumulative Number of Claims	$ 37									$ 37

Claim and Claim Adjustment E_13

Claim and Claim Adjustment Expense Reserves (Specialty - Other Professional Liability and Management Liability - Net Incurred Claims and Allocated Claim Adjustment Expenses) (Details) - Other Professional Liability and Management Liability - Specialty $ in Millions	Dec. 31, 2018USD ($)claims	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)	Dec. 31, 2012USD ($)	Dec. 31, 2011USD ($)	Dec. 31, 2010USD ($)	Dec. 31, 2009USD ($)
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 8,559
IBNR	1,948
2,009
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	892	$ 904	$ 906	$ 897	$ 903	$ 893	$ 903	$ 908	$ 875	$ 831
IBNR	$ 18
Cumulative Number of Claims | claims	17,374
2,010
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 821	827	824	837	847	848	848	828	$ 828
IBNR	$ 19
Cumulative Number of Claims | claims	17,888
2,011
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 888	899	911	944	949	934	908	$ 880
IBNR	$ 39
Cumulative Number of Claims | claims	18,728
2,012
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 833	846	840	878	887	909	$ 923
IBNR	$ 41
Cumulative Number of Claims | claims	18,491
2,013
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 863	866	885	926	894	$ 884
IBNR	$ 65
Cumulative Number of Claims | claims	17,918
2,014
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 835	831	885	898	$ 878
IBNR	$ 88
Cumulative Number of Claims | claims	17,515
2,015
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 832	877	892	$ 888
IBNR	$ 194
Cumulative Number of Claims | claims	17,333
2,016
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 900	900	$ 901
IBNR	$ 279
Cumulative Number of Claims | claims	17,787
2,017
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 845	$ 847
IBNR	$ 479
Cumulative Number of Claims | claims	17,780
2,018
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 850
IBNR	$ 726
Cumulative Number of Claims | claims	16,564

Claim and Claim Adjustment E_14

Claim and Claim Adjustment Expense Reserves (Specialty - Other Professional Liability and Management Liability - Net Cumulative Paid Claim and Claim Adjustment Expenses) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Net liability for unpaid claim and claim adjustment expenses for accident years prior to 2009	$ 4,285	$ 4,366	$ 4,167
Total net liability for unpaid claim and claim adjustment expenses	17,965	18,070	18,249	$ 18,576
Specialty
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Total net liability for unpaid claim and claim adjustment expenses	4,831	5,007
Other Professional Liability and Management Liability | Specialty
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	5,864
Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented	2,695
Net liability for unpaid claim and claim adjustment expenses for accident years prior to 2009	90
Liability for unallocated claim adjustment expenses for accident years presented	64
Total net liability for unpaid claim and claim adjustment expenses	2,849
Other Professional Liability and Management Liability | 2009 | Specialty
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	844	825	801	772	$ 722	$ 641	$ 553	$ 361	$ 195	$ 37
Other Professional Liability and Management Liability | 2010 | Specialty
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	784	752	721	670	630	541	405	204	$ 31
Other Professional Liability and Management Liability | 2011 | Specialty
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	796	781	726	683	605	503	314	$ 71
Other Professional Liability and Management Liability | 2012 | Specialty
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	755	711	651	573	400	248	$ 56
Other Professional Liability and Management Liability | 2013 | Specialty
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	754	702	618	447	249	$ 54
Other Professional Liability and Management Liability | 2014 | Specialty
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	647	515	392	223	$ 51
Other Professional Liability and Management Liability | 2015 | Specialty
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	542	404	234	$ 60
Other Professional Liability and Management Liability | 2016 | Specialty
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	466	248	$ 64
Other Professional Liability and Management Liability | 2017 | Specialty
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	222	$ 57
Other Professional Liability and Management Liability | 2018 | Specialty
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	$ 54

Claim and Claim Adjustment E_15

Claim and Claim Adjustment Expense Reserves (Specialty - Other Professional Liability and Management Liability - Net Strengthening or Releasing of Prior Accident Year Reserves) (Details) - Specialty - USD ($) $ in Millions	12 Months Ended									24 Months Ended	36 Months Ended	48 Months Ended	60 Months Ended	72 Months Ended	84 Months Ended	96 Months Ended	108 Months Ended	120 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018
Claims Development [Line Items]
Net prior year claim and allocated claim adjustment expense reserve development, Other Professional Liability and Management Liability	$ (127)	$ (126)	$ (140)
Other Professional Liability and Management Liability
Claims Development [Line Items]
Cumulative Number of Claims	(88)	(94)	(125)
Total net development for accident years prior to 2009	(32)	(25)	(15)
Total unallocated claim adjustment expense development	(7)	(7)	0
Net prior year claim and allocated claim adjustment expense reserve development, Other Professional Liability and Management Liability	(127)	(126)	(140)
Other Professional Liability and Management Liability | 2009
Claims Development [Line Items]
Cumulative Number of Claims	(12)	(2)	9	$ (6)	$ 10	$ (10)	$ (5)	$ 33	$ 44									$ 61
Other Professional Liability and Management Liability | 2010
Claims Development [Line Items]
Cumulative Number of Claims	(6)	3	(13)	(10)	(1)	0	20	$ 0									$ (7)
Other Professional Liability and Management Liability | 2011
Claims Development [Line Items]
Cumulative Number of Claims	(11)	(12)	(33)	(5)	15	26	$ 28									$ 8
Other Professional Liability and Management Liability | 2012
Claims Development [Line Items]
Cumulative Number of Claims	(13)	6	(38)	(9)	(22)	$ (14)									$ (90)
Other Professional Liability and Management Liability | 2013
Claims Development [Line Items]
Cumulative Number of Claims	(3)	(19)	(41)	32	$ 10									$ (21)
Other Professional Liability and Management Liability | 2014
Claims Development [Line Items]
Cumulative Number of Claims	4	(54)	(13)	$ 20									$ (43)
Other Professional Liability and Management Liability | 2015
Claims Development [Line Items]
Cumulative Number of Claims	(45)	(15)	$ 4									$ (56)
Other Professional Liability and Management Liability | 2016
Claims Development [Line Items]
Cumulative Number of Claims	0	$ (1)									$ (1)
Other Professional Liability and Management Liability | 2017
Claims Development [Line Items]
Cumulative Number of Claims	$ (2)									$ (2)

Claim and Claim Adjustment E_16

Claim and Claim Adjustment Expense Reserves (Specialty - Surety - Net Incurred Claims and Allocated Claim Adjustment Expenses) (Details) - Surety - Specialty $ in Millions	Dec. 31, 2018USD ($)claims	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)	Dec. 31, 2012USD ($)	Dec. 31, 2011USD ($)	Dec. 31, 2010USD ($)	Dec. 31, 2009USD ($)
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 778
IBNR	305
2,009
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	52	$ 53	$ 53	$ 52	$ 59	$ 68	$ 85	$ 103	$ 114	$ 114
IBNR	$ 1
Cumulative Number of Claims | claims	6,688
2,010
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 61	59	63	66	76	84	111	112	$ 112
IBNR	$ 1
Cumulative Number of Claims | claims	5,971
2,011
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 62	66	70	75	87	116	121	$ 120
IBNR	$ 1
Cumulative Number of Claims | claims	5,808
2,012
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 39	45	52	70	98	122	$ 120
IBNR	$ 2
Cumulative Number of Claims | claims	5,559
2,013
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 87	91	106	115	121	$ 120
IBNR	$ 6
Cumulative Number of Claims | claims	5,039
2,014
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 60	69	94	124	$ 123
IBNR	$ 19
Cumulative Number of Claims | claims	5,036
2,015
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 79	104	131	$ 131
IBNR	$ 36
Cumulative Number of Claims | claims	4,887
2,016
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 109	124	$ 124
IBNR	$ 60
Cumulative Number of Claims | claims	5,185
2,017
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 115	$ 120
IBNR	$ 78
Cumulative Number of Claims | claims	4,936
2,018
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 114
IBNR	$ 101
Cumulative Number of Claims | claims	3,105

Claim and Claim Adjustment E_17

Claim and Claim Adjustment Expense Reserves (Specialty - Surety - Net Cumulative Paid Claim and Claim Adjustment Expenses) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Net liability for unpaid claim and claim adjustment expenses for accident years prior to 2009	$ 4,285	$ 4,366	$ 4,167
Total net liability for unpaid claim and claim adjustment expenses	17,965	18,070	18,249	$ 18,576
Specialty
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Total net liability for unpaid claim and claim adjustment expenses	4,831	5,007
Surety | Specialty
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	436
Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented	342
Net liability for unpaid claim and claim adjustment expenses for accident years prior to 2009	7
Liability for unallocated claim adjustment expenses for accident years presented	30
Total net liability for unpaid claim and claim adjustment expenses	379
Surety | Specialty | 2009
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	47	47	47	46	$ 45	$ 43	$ 41	$ 34	$ 24	$ 13
Surety | Specialty | 2010
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	52	52	55	58	57	55	50	34	$ 13
Surety | Specialty | 2011
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	57	56	60	60	58	55	42	$ 19
Surety | Specialty | 2012
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	37	36	35	35	34	32	$ 5
Surety | Specialty | 2013
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	78	78	78	69	40	$ 16
Surety | Specialty | 2014
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	38	36	38	30	$ 7
Surety | Specialty | 2015
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	40	38	26	$ 7
Surety | Specialty | 2016
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	45	37	$ 5
Surety | Specialty | 2017
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	37	$ 23
Surety | Specialty | 2018
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	$ 5

Claim and Claim Adjustment E_18

Claim and Claim Adjustment Expense Reserves (Specialty - Surety - Net Strengthening or Releasing of Prior Accident Year Reserves) (Details) - Specialty - USD ($) $ in Millions	12 Months Ended									24 Months Ended	36 Months Ended	48 Months Ended	60 Months Ended	72 Months Ended	84 Months Ended	96 Months Ended	108 Months Ended	120 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018
Claims Development [Line Items]
Net prior year claim and allocated claim adjustment expense reserve development, Surety	$ (70)	$ (84)	$ (63)
Surety
Claims Development [Line Items]
Cumulative Number of Claims	(67)	(82)	(64)
Total net development for accident years prior to 2009	(3)	1	1
Total unallocated claim adjustment expense development	0	(3)	0
Net prior year claim and allocated claim adjustment expense reserve development, Surety	(70)	(84)	(63)
Surety | 2009
Claims Development [Line Items]
Cumulative Number of Claims	(1)	0	1	$ (7)	$ (9)	$ (17)	$ (18)	$ (11)	$ 0									$ (62)
Surety | 2010
Claims Development [Line Items]
Cumulative Number of Claims	2	(4)	(3)	(10)	(8)	(27)	(1)	$ 0									$ (51)
Surety | 2011
Claims Development [Line Items]
Cumulative Number of Claims	(4)	(4)	(5)	(12)	(29)	(5)	$ 1									$ (58)
Surety | 2012
Claims Development [Line Items]
Cumulative Number of Claims	(6)	(7)	(18)	(28)	(24)	$ 2									$ (81)
Surety | 2013
Claims Development [Line Items]
Cumulative Number of Claims	(4)	(15)	(9)	(6)	$ 1									$ (33)
Surety | 2014
Claims Development [Line Items]
Cumulative Number of Claims	(9)	(25)	(30)	$ 1									$ (63)
Surety | 2015
Claims Development [Line Items]
Cumulative Number of Claims	(25)	(27)	$ 0									$ (52)
Surety | 2016
Claims Development [Line Items]
Cumulative Number of Claims	(15)	$ 0									$ (15)
Surety | 2017
Claims Development [Line Items]
Cumulative Number of Claims	$ (5)									$ (5)

Claim and Claim Adjustment E_19

Claim and Claim Adjustment Expense Reserves (Commercial - Net prior year claim and allocated claim adjustment expense reserve development) (Details) - Commercial - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Liability for Claims and Claims Adjustment Expense [Line Items]
Commercial Auto	$ 1	$ (35)	$ (47)
General Liability	32	(24)	(65)
Workers' Compensation	(32)	(63)	145
Property and Other	(26)	7	(18)
Total pretax (favorable) unfavorable development	$ (25)	$ (115)	$ 15

Claim and Claim Adjustment E_20

Claim and Claim Adjustment Expense Reserves (Commercial - Commercial Auto - Short Duration Contracts) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total net liability for unpaid claim and claim adjustment expenses	$ 17,965	$ 18,070	$ 18,249	$ 18,576
Commercial
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total net liability for unpaid claim and claim adjustment expenses	7,998	$ 8,136
Commercial Auto | Commercial
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total net liability for unpaid claim and claim adjustment expenses	412
General Liability | Commercial
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total net liability for unpaid claim and claim adjustment expenses	3,195
Workers' Compensation | Commercial
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total net liability for unpaid claim and claim adjustment expenses	3,968
Property and Other | Commercial
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total net liability for unpaid claim and claim adjustment expenses	$ 423

Claim and Claim Adjustment E_21

Claim and Claim Adjustment Expense Reserves (Commercial - Commercial Auto - Net Incurred Claims and Allocated Claim Adjustment Expenses) (Details) - Commercial Auto - Commercial $ in Millions	Dec. 31, 2018USD ($)claims	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)	Dec. 31, 2012USD ($)	Dec. 31, 2011USD ($)	Dec. 31, 2010USD ($)	Dec. 31, 2009USD ($)
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 2,411
IBNR	239
2,009
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	277	$ 276	$ 276	$ 278	$ 281	$ 285	$ 282	$ 280	$ 276	$ 291
IBNR	$ 0
Cumulative Number of Claims | claims	48,499
2,010
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 288	288	289	293	298	291	287	283	$ 267
IBNR	$ 1
Cumulative Number of Claims | claims	48,030
2,011
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 294	294	294	300	302	288	281	$ 268
IBNR	$ 4
Cumulative Number of Claims | claims	47,905
2,012
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 299	299	307	303	299	289	$ 275
IBNR	$ 6
Cumulative Number of Claims | claims	46,288
2,013
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 245	245	249	265	265	$ 246
IBNR	$ 7
Cumulative Number of Claims | claims	39,429
2,014
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 205	205	212	223	$ 234
IBNR	$ 9
Cumulative Number of Claims | claims	33,609
2,015
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 190	190	199	$ 201
IBNR	$ 22
Cumulative Number of Claims | claims	30,388
2,016
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 186	186	$ 198
IBNR	$ 27
Cumulative Number of Claims | claims	30,342
2,017
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 198	$ 199
IBNR	$ 45
Cumulative Number of Claims | claims	30,580
2,018
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 229
IBNR	$ 118
Cumulative Number of Claims | claims	28,602

Claim and Claim Adjustment E_22

Claim and Claim Adjustment Expense Reserves (Commerical - Commercial Auto - Net Cumulative Paid Claim and Claim Adjustment Expenses) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Net liability for unpaid claim and claim adjustment expenses for accident years prior to 2009	$ 4,285	$ 4,366	$ 4,167
Total net liability for unpaid claim and claim adjustment expenses	17,965	18,070	18,249	$ 18,576
Commercial
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Total net liability for unpaid claim and claim adjustment expenses	7,998	8,136
Commercial Auto | Commercial
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	2,016
Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented	395
Net liability for unpaid claim and claim adjustment expenses for accident years prior to 2009	6
Liability for unallocated claim adjustment expenses for accident years presented	11
Total net liability for unpaid claim and claim adjustment expenses	412
Commercial Auto | Commercial | 2009
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	277	275	274	274	$ 272	$ 261	$ 233	$ 191	$ 130	$ 73
Commercial Auto | Commercial | 2010
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	287	287	286	281	271	246	203	141	$ 74
Commercial Auto | Commercial | 2011
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	289	287	284	274	248	199	145	$ 79
Commercial Auto | Commercial | 2012
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	290	285	282	259	220	160	$ 78
Commercial Auto | Commercial | 2013
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	234	225	200	168	135	$ 74
Commercial Auto | Commercial | 2014
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	187	166	137	102	$ 64
Commercial Auto | Commercial | 2015
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	153	130	96	$ 52
Commercial Auto | Commercial | 2016
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	126	93	$ 52
Commercial Auto | Commercial | 2017
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	107	$ 58
Commercial Auto | Commercial | 2018
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	$ 66

Claim and Claim Adjustment E_23

Claim and Claim Adjustment Expense Reserves (Commercial - Commercial Auto - Net Strengthening or Releasing of Prior Accident Year Reserves) (Details) - Commercial - USD ($) $ in Millions	12 Months Ended									24 Months Ended	36 Months Ended	48 Months Ended	60 Months Ended	72 Months Ended	84 Months Ended	96 Months Ended	108 Months Ended	120 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net prior year claim and allocated claim adjustment expense reserve development, Commercial Auto	$ 1	$ (35)	$ (47)
Commercial Auto
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	0	(41)	(37)
Total net development for accident years prior to 2009	0	4	(10)
Total unallocated claim adjustment expense development	1	2	0
Net prior year claim and allocated claim adjustment expense reserve development, Commercial Auto	1	(35)	(47)
2009 | Commercial Auto
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	1	0	(2)	$ (3)	$ (4)	$ 3	$ 2	$ 4	$ (15)									$ (14)
2010 | Commercial Auto
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	0	(1)	(4)	(5)	7	4	4	$ 16									$ 21
2011 | Commercial Auto
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	0	0	(6)	(2)	14	7	$ 13									$ 26
2012 | Commercial Auto
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	0	(8)	4	4	10	$ 14									$ 24
2013 | Commercial Auto
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	0	(4)	(16)	0	$ 19									$ (1)
2014 | Commercial Auto
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	0	(7)	(11)	$ (11)									$ (29)
2015 | Commercial Auto
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	0	(9)	$ (2)									$ (11)
2016 | Commercial Auto
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	0	$ (12)									$ (12)
2017 | Commercial Auto
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	$ (1)									$ (1)

Claim and Claim Adjustment E_24

Claim and Claim Adjustment Expense Reserves (Commercial - General Liability - Net Incurred Claims and Allocated Claim Adjustment Expenses) (Details) - General Liability - Commercial $ in Millions	Dec. 31, 2018USD ($)claims	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)	Dec. 31, 2012USD ($)	Dec. 31, 2011USD ($)	Dec. 31, 2010USD ($)	Dec. 31, 2009USD ($)
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 6,549
IBNR	1,586
2,009
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	755	$ 755	$ 754	$ 755	$ 756	$ 752	$ 755	$ 733	$ 716	$ 662
IBNR	$ 16
Cumulative Number of Claims | claims	44,934
2,010
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 691	691	697	726	750	709	658	664	$ 646
IBNR	$ 24
Cumulative Number of Claims | claims	44,144
2,011
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 669	670	681	676	677	631	589	$ 591
IBNR	$ 26
Cumulative Number of Claims | claims	39,283
2,012
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 635	635	619	636	639	611	$ 587
IBNR	$ 46
Cumulative Number of Claims | claims	35,083
2,013
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 623	613	655	650	655	$ 650
IBNR	$ 51
Cumulative Number of Claims | claims	33,420
2,014
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 635	631	654	658	$ 653
IBNR	$ 71
Cumulative Number of Claims | claims	27,736
2,015
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 589	574	576	$ 581
IBNR	$ 122
Cumulative Number of Claims | claims	23,471
2,016
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 667	659	$ 623
IBNR	$ 265
Cumulative Number of Claims | claims	23,078
2,017
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 632	$ 632
IBNR	$ 412
Cumulative Number of Claims | claims	19,716
2,018
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 653
IBNR	$ 553
Cumulative Number of Claims | claims	13,336

Claim and Claim Adjustment E_25

Claim and Claim Adjustment Expense Reserves (Commercial - General Liability - Net Cumulative Paid Claim and Claim Adjustment Expenses) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Net liability for unpaid claim and claim adjustment expenses for accident years prior to 2009	$ 4,285	$ 4,366	$ 4,167
Total net liability for unpaid claim and claim adjustment expenses	17,965	18,070	18,249	$ 18,576
Commercial
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Total net liability for unpaid claim and claim adjustment expenses	7,998	8,136
General Liability | Commercial
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	4,342
Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented	2,207
Net liability for unpaid claim and claim adjustment expenses for accident years prior to 2009	927
Liability for unallocated claim adjustment expenses for accident years presented	61
Total net liability for unpaid claim and claim adjustment expenses	3,195
General Liability | Commercial | 2009
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	727	721	701	663	$ 625	$ 576	$ 468	$ 305	$ 124	$ 33
General Liability | Commercial | 2010
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	656	652	642	611	561	429	280	145	$ 27
General Liability | Commercial | 2011
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	622	602	568	517	411	273	148	$ 28
General Liability | Commercial | 2012
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	559	510	454	374	247	132	$ 28
General Liability | Commercial | 2013
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	510	450	352	240	128	$ 31
General Liability | Commercial | 2014
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	481	376	247	119	$ 31
General Liability | Commercial | 2015
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	357	230	110	$ 19
General Liability | Commercial | 2016
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	279	163	$ 32
General Liability | Commercial | 2017
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	118	$ 23
General Liability | Commercial | 2018
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	$ 33

Claim and Claim Adjustment E_26

Claim and Claim Adjustment Expense Reserves (Commercial - General Liability - Net Strengthening or Releasing of Prior Accident Year Reserves) (Details) - Commercial - USD ($) $ in Millions	12 Months Ended									24 Months Ended	36 Months Ended	48 Months Ended	60 Months Ended	72 Months Ended	84 Months Ended	96 Months Ended	108 Months Ended	120 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net prior year claim and allocated claim adjustment expense reserve development, General Liability	$ 32	$ (24)	$ (65)
General Liability
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	36	(31)	(46)
Total net development for accident years prior to 2009	0	(1)	(19)
Total unallocated claim adjustment expense development	(4)	8	0
Net prior year claim and allocated claim adjustment expense reserve development, General Liability	32	(24)	(65)
General Liability | 2009
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	0	1	(1)	$ (1)	$ 4	$ (3)	$ 22	$ 17	$ 54									$ 93
General Liability | 2010
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	0	(6)	(29)	(24)	41	51	(6)	$ 18									$ 45
General Liability | 2011
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	(1)	(11)	5	(1)	46	42	$ (2)									$ 78
General Liability | 2012
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	0	16	(17)	(3)	28	$ 24									$ 48
General Liability | 2013
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	10	(42)	5	(5)	$ 5									$ (27)
General Liability | 2014
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	4	(23)	(4)	$ 5									$ (18)
General Liability | 2015
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	15	(2)	$ (5)									$ 8
General Liability | 2016
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	8	$ 36									$ 44
General Liability | 2017
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	$ 0									$ 0

Claim and Claim Adjustment E_27

Claim and Claim Adjustment Expense Reserves (Commercial - Workers' Compensation - Net Incurred Claims and Allocated Claim Adjustment Expenses) (Details) - Workers' Compensation - Commercial $ in Millions	Dec. 31, 2018USD ($)claims	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)	Dec. 31, 2012USD ($)	Dec. 31, 2011USD ($)	Dec. 31, 2010USD ($)	Dec. 31, 2009USD ($)
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 5,445
IBNR	1,130
2,009
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	650	$ 649	$ 638	$ 631	$ 626	$ 616	$ 611	$ 609	$ 599	$ 592
IBNR	$ 46
Cumulative Number of Claims | claims	51,822
2,010
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 732	733	730	710	698	676	654	632	$ 583
IBNR	$ 44
Cumulative Number of Claims | claims	49,106
2,011
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 674	676	676	651	659	647	641	$ 607
IBNR	$ 27
Cumulative Number of Claims | claims	45,637
2,012
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 671	673	678	669	659	627	$ 601
IBNR	$ 59
Cumulative Number of Claims | claims	42,477
2,013
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 582	593	618	592	572	$ 537
IBNR	$ 86
Cumulative Number of Claims | claims	38,665
2,014
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 450	452	479	480	$ 467
IBNR	$ 104
Cumulative Number of Claims | claims	33,465
2,015
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 408	406	431	$ 422
IBNR	$ 146
Cumulative Number of Claims | claims	31,828
2,016
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 396	405	$ 426
IBNR	$ 171
Cumulative Number of Claims | claims	31,905
2,017
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 432	$ 440
IBNR	$ 171
Cumulative Number of Claims | claims	32,811
2,018
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 450
IBNR	$ 276
Cumulative Number of Claims | claims	30,399

Claim and Claim Adjustment E_28

Claim and Claim Adjustment Expense Reserves (Commercial - Workers' Compensation - Net Cumulative Paid Claim and Claim Adjustment Expensess) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Net liability for unpaid claim and claim adjustment expenses for accident years prior to 2009	$ 4,285	$ 4,366	$ 4,167
Total net liability for unpaid claim and claim adjustment expenses	17,965	18,070	18,249	$ 18,576
Commercial
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Total net liability for unpaid claim and claim adjustment expenses	7,998	8,136
Workers' Compensation | Commercial
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	3,578
Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented	1,867
Net liability for unpaid claim and claim adjustment expenses for accident years prior to 2009	2,131
Other	(32)
Liability for unallocated claim adjustment expenses for accident years presented	2
Total net liability for unpaid claim and claim adjustment expenses	3,968
Workers' Compensation | 2009 | Commercial
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	557	549	525	503	$ 476	$ 443	$ 388	$ 321	$ 227	$ 89
Workers' Compensation | 2010 | Commercial
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	625	615	577	542	510	442	359	251	$ 97
Workers' Compensation | 2011 | Commercial
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	571	564	522	478	438	358	249	$ 99
Workers' Compensation | 2012 | Commercial
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	524	509	470	416	342	232	$ 87
Workers' Compensation | 2013 | Commercial
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	419	417	370	300	213	$ 80
Workers' Compensation | 2014 | Commercial
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	282	258	215	159	$ 61
Workers' Compensation | 2015 | Commercial
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	212	180	131	$ 51
Workers' Compensation | 2016 | Commercial
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	169	129	$ 53
Workers' Compensation | 2017 | Commercial
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	151	$ 63
Workers' Compensation | 2018 | Commercial
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	$ 68

Claim and Claim Adjustment E_29

Claim and Claim Adjustment Expense Reserves (Commercial - Workers' Compensation - Net Strengthening or Releasing of Prior Accident Year Reserves) (Details) - Commercial - USD ($) $ in Millions	12 Months Ended									24 Months Ended	36 Months Ended	48 Months Ended	60 Months Ended	72 Months Ended	84 Months Ended	96 Months Ended	108 Months Ended	120 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net prior year claim and allocated claim adjustment expense reserve development, Workers' Compensation	$ (32)	$ (63)	$ 145
Workers' Compensation
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	(32)	(89)	95
Adjustment for development on a discounted basis	0	(3)	(3)
Total net development for accident years prior to 2009	7	28	53
Total unallocated claim adjustment expense development	(7)	1	0
Net prior year claim and allocated claim adjustment expense reserve development, Workers' Compensation	(32)	(63)	145
Workers' Compensation | 2009
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	1	11	7	$ 5	$ 10	$ 5	$ 2	$ 10	$ 7									$ 58
Workers' Compensation | 2010
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	(1)	3	20	12	22	22	22	$ 49									$ 149
Workers' Compensation | 2011
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	(2)	0	25	(8)	12	6	$ 34									$ 67
Workers' Compensation | 2012
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	(2)	(5)	9	10	32	$ 26									$ 70
Workers' Compensation | 2013
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	(11)	(25)	26	20	$ 35									$ 45
Workers' Compensation | 2014
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	(2)	(27)	(1)	$ 13									$ (17)
Workers' Compensation | 2015
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	2	(25)	$ 9									$ (14)
Workers' Compensation | 2016
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	(9)	$ (21)									$ (30)
Workers' Compensation | 2017
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	$ (8)									$ (8)

Claim and Claim Adjustment E_30

Claim and Claim Adjustment Expense Reserves (International - Net prior year claim and allocated claim adjustment expense reserve development) (Details) - International - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Liability for Claims and Claims Adjustment Expense [Line Items]
Casualty	$ (17)	$ 9	$ (29)
Property	17	(16)	(21)
Energy and Marine	(19)	(12)	(18)
Specialty	27	12	19
Healthcare and Technology	(12)	(2)	(9)
Total pretax (favorable) unfavorable development	$ (4)	$ (9)	$ (58)

Claim and Claim Adjustment E_31

Claim and Claim Adjustment Expense Reserves (International - Short Duration Contracts) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total net liability for unpaid claim and claim adjustment expenses	$ 17,965	$ 18,070	$ 18,249	$ 18,576
International
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total net liability for unpaid claim and claim adjustment expenses	1,524	$ 1,432
Excluding Hardy | International
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total net liability for unpaid claim and claim adjustment expenses	1,059
Hardy | International
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total net liability for unpaid claim and claim adjustment expenses	$ 465

Claim and Claim Adjustment E_32

Claim and Claim Adjustment Expense Reserves (International - Excluding Hardy - Net Incurred Claims and Allocated Claim Adjustment Expenses) (Details) - Excluding Hardy - International $ in Millions	Dec. 31, 2018USD ($)claims	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)	Dec. 31, 2012USD ($)	Dec. 31, 2011USD ($)	Dec. 31, 2010USD ($)	Dec. 31, 2009USD ($)
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 2,683
IBNR	546
2,009
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	219	$ 216	$ 218	$ 226	$ 236	$ 239	$ 253	$ 253	$ 251	$ 254
IBNR	$ 8
Cumulative Number of Claims | claims	20,257
2,010
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 184	188	195	201	208	217	223	229	$ 232
IBNR	$ 8
Cumulative Number of Claims | claims	21,949
2,011
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 216	219	221	227	239	258	266	$ 265
IBNR	$ 9
Cumulative Number of Claims | claims	24,585
2,012
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 236	244	251	251	258	273	$ 266
IBNR	$ 20
Cumulative Number of Claims | claims	24,975
2,013
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 250	257	261	281	289	$ 287
IBNR	$ 25
Cumulative Number of Claims | claims	23,909
2,014
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 271	279	290	290	$ 275
IBNR	$ 38
Cumulative Number of Claims | claims	24,874
2,015
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 286	304	305	$ 289
IBNR	$ 51
Cumulative Number of Claims | claims	23,239
2,016
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 289	302	$ 284
IBNR	$ 79
Cumulative Number of Claims | claims	17,557
2,017
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 363	$ 300
IBNR	$ 134
Cumulative Number of Claims | claims	17,865
2,018
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 369
IBNR	$ 174
Cumulative Number of Claims | claims	16,565

Claim and Claim Adjustment E_33

Claim and Claim Adjustment Expense Reserves (International - Excluding Hardy - Net Cumulative Paid Claim and Claim Adjustment Expenses) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Net liability for unpaid claim and claim adjustment expenses for accident years prior to 2009	$ 4,285	$ 4,366	$ 4,167
Total net liability for unpaid claim and claim adjustment expenses	17,965	18,070	18,249	$ 18,576
International
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Total net liability for unpaid claim and claim adjustment expenses	1,524	1,432
Excluding Hardy | International
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	1,687
Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented	996
Net liability for unpaid claim and claim adjustment expenses for accident years prior to 2009	39
Liability for unallocated claim adjustment expenses for accident years presented	24
Total net liability for unpaid claim and claim adjustment expenses	1,059
Excluding Hardy | 2009 | International
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	198	190	185	174	$ 162	$ 153	$ 137	$ 122	$ 92	$ 39
Excluding Hardy | 2010 | International
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	169	167	164	156	146	133	119	96	$ 48
Excluding Hardy | 2011 | International
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	185	181	174	162	149	135	114	$ 44
Excluding Hardy | 2012 | International
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	201	191	180	164	144	112	$ 43
Excluding Hardy | 2013 | International
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	179	169	155	138	112	$ 49
Excluding Hardy | 2014 | International
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	182	165	148	120	$ 51
Excluding Hardy | 2015 | International
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	181	161	131	$ 55
Excluding Hardy | 2016 | International
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	157	131	$ 66
Excluding Hardy | 2017 | International
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	145	$ 64
Excluding Hardy | 2018 | International
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	$ 90

Claim and Claim Adjustment E_34

Claim and Claim Adjustment Expense Reserves (International - Excluding Hardy - Net Strengthening or Releasing of Prior Accident Year Reserves) (Details) - Excluding Hardy - International - USD ($) $ in Millions	12 Months Ended									24 Months Ended	36 Months Ended	48 Months Ended	60 Months Ended	72 Months Ended	84 Months Ended	96 Months Ended	108 Months Ended	120 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018
2,009
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	$ 3	$ (2)	$ (8)	$ (10)	$ (3)	$ (14)	$ 0	$ 2	$ (3)									$ (35)
2,010
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	(4)	(7)	(6)	(7)	(9)	(6)	(6)	$ (3)									$ (48)
2,011
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	(3)	(2)	(6)	(12)	(19)	(8)	$ 1									$ (49)
2,012
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	(8)	(7)	0	(7)	(15)	$ 7									$ (30)
2,013
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	(7)	(4)	(20)	(8)	$ 2									$ (37)
2,014
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	(8)	(11)	0	$ 15									$ (4)
2,015
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	(18)	(1)	$ 16									$ (3)
2,016
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	(13)	$ 18									$ 5
2,017
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	$ 63									$ 63

Claim and Claim Adjustment E_35

Claim and Claim Adjustment Expense Reserves (International - Hardy - Net Incurred Claims and Allocated Claim Adjustment Expenses) (Details) - Hardy - International $ in Millions	Dec. 31, 2018USD ($)claims	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)	Dec. 31, 2012USD ($)
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 1,550
Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented	456
IBNR	185
2,009
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Net Claim and Claim Adjustment Expense Reserves at Acquisition							$ 11
Incurred claims and allocated claim adjustment expense, net	(3)	$ (3)	$ (2)	$ 1	$ (4)	$ 6	0
Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented							12
IBNR	$ (2)
Cumulative Number of Claims | claims	3,856
2,010
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Net Claim and Claim Adjustment Expense Reserves at Acquisition							48
Incurred claims and allocated claim adjustment expense, net	$ 50	51	52	46	52	47	(9)
Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented							38
IBNR	$ 0
Cumulative Number of Claims | claims	4,540
2,011
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Net Claim and Claim Adjustment Expense Reserves at Acquisition							125
Incurred claims and allocated claim adjustment expense, net	$ 140	137	137	138	134	134	(1)
Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented							124
IBNR	$ (2)
Cumulative Number of Claims | claims	6,252
2,012
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Net Claim and Claim Adjustment Expense Reserves at Acquisition							33
Incurred claims and allocated claim adjustment expense, net	$ 115	113	113	119	112	104	71
Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented							$ 104
IBNR	$ 1
Cumulative Number of Claims | claims	6,900
2,013
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 144	140	139	138	146	$ 130
IBNR	$ 4
Cumulative Number of Claims | claims	7,624
2,014
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 170	170	176	182	$ 184
IBNR	$ 2
Cumulative Number of Claims | claims	8,097
2,015
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 178	177	179	$ 190
IBNR	$ 3
Cumulative Number of Claims | claims	8,968
2,016
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 234	245	$ 227
IBNR	$ 28
Cumulative Number of Claims | claims	9,536
2,017
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 252	$ 244
IBNR	$ 48
Cumulative Number of Claims | claims	10,309
2,018
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 270
IBNR	$ 103
Cumulative Number of Claims | claims	7,563

Claim and Claim Adjustment E_36

Claim and Claim Adjustment Expense Reserves (International - Hardy - Net Cumulative Paid Claim and Claim Adjustment Expenses) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Net liability for unpaid claim and claim adjustment expenses for accident years prior to 2009	$ 4,285	$ 4,366	$ 4,167
Total net liability for unpaid claim and claim adjustment expenses	17,965	18,070	18,249	$ 18,576
International
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Total net liability for unpaid claim and claim adjustment expenses	1,524	1,432
Hardy | International
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	1,094
Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented	456
Net liability for unpaid claim and claim adjustment expenses for accident years prior to 2009	0
Liability for unallocated claim adjustment expenses for accident years presented	9
Total net liability for unpaid claim and claim adjustment expenses	465
Hardy | International | 2009
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	(4)	(5)	(4)	(4)	$ (4)	$ (2)	$ 2
Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented							12
Hardy | International | 2010
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	46	48	47	45	42	35	19
Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented							38
Hardy | International | 2011
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	134	132	131	127	123	83	30
Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented							124
Hardy | International | 2012
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	110	109	106	109	100	79	14
Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented							$ 104
Hardy | International | 2013
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	133	130	126	120	101	$ 38
Hardy | International | 2014
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	155	150	141	122	$ 56
Hardy | International | 2015
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	144	129	98	$ 29
Hardy | International | 2016
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	171	144	$ 63
Hardy | International | 2017
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	150	$ 53
Hardy | International | 2018
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	$ 55

Claim and Claim Adjustment E_37

Claim and Claim Adjustment Expense Reserves (International - Hardy - Net Strengthening or Releasing of Prior Accident Year Reserves) (Details) - International - Hardy - USD ($) $ in Millions	12 Months Ended							24 Months Ended	36 Months Ended	48 Months Ended	60 Months Ended	72 Months Ended	84 Months Ended	96 Months Ended	108 Months Ended	120 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018
2,009
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	$ 0	$ (1)	$ (3)	$ 5	$ (10)	$ (6)	$ 1									$ (14)
2,010
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	(1)	(1)	6	(6)	5	9	(10)								$ 2
2,011
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	3	0	(1)	4	0	10	$ (1)							$ 15
2,012
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	2	0	(6)	7	8	$ 0							$ 11
2,013
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	4	1	1	(8)	$ 16							$ 14
2,014
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	0	(6)	(6)	$ (2)							$ (14)
2,015
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	1	(2)	$ (11)							$ (12)
2,016
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	(11)	$ 18							$ 7
2,017
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	$ 8							$ 8

Claim and Claim Adjustment E_38

Claim and Claim Adjustment Expense Reserves (Historical Claims Duration) (Details)	Dec. 31, 2018
Medical Professional Liability | Specialty
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Short-duration Insurance Contracts, Historical Claims Duration, Year One	3.80%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	19.70%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	24.30%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	20.10%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	12.10%
Short-duration Insurance Contracts, Historical Claims Duration, Year Six	7.20%
Short-duration Insurance Contracts, Historical Claims Duration, Year Seven	4.50%
Short-duration Insurance Contracts, Historical Claims Duration, Year Eight	2.50%
Short-duration Insurance Contracts, Historical Claims Duration, Year Nine	1.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Ten	2.90%
Short-Duration Insurance Contracts, Historical Claims Duration, Net	98.10%
Other Professional Liability and Management Liability | Specialty
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Short-duration Insurance Contracts, Historical Claims Duration, Year One	6.20%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	21.50%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	21.30%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	17.40%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	10.70%
Short-duration Insurance Contracts, Historical Claims Duration, Year Six	6.40%
Short-duration Insurance Contracts, Historical Claims Duration, Year Seven	5.80%
Short-duration Insurance Contracts, Historical Claims Duration, Year Eight	2.90%
Short-duration Insurance Contracts, Historical Claims Duration, Year Nine	3.30%
Short-duration Insurance Contracts, Historical Claims Duration, Year Ten	2.10%
Short-Duration Insurance Contracts, Historical Claims Duration, Net	97.60%
Surety | Specialty
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Short-duration Insurance Contracts, Historical Claims Duration, Year One	21.60%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	37.90%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	21.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	7.90%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	2.10%
Short-duration Insurance Contracts, Historical Claims Duration, Year Six	1.60%
Short-duration Insurance Contracts, Historical Claims Duration, Year Seven	(1.70%)
Short-duration Insurance Contracts, Historical Claims Duration, Year Eight	(0.50%)
Short-duration Insurance Contracts, Historical Claims Duration, Year Nine	0.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Ten	0.00%
Short-Duration Insurance Contracts, Historical Claims Duration, Net	89.90%
Commercial Auto | Commercial
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Short-duration Insurance Contracts, Historical Claims Duration, Year One	28.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	23.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	18.50%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	14.20%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	9.30%
Short-duration Insurance Contracts, Historical Claims Duration, Year Six	3.10%
Short-duration Insurance Contracts, Historical Claims Duration, Year Seven	1.30%
Short-duration Insurance Contracts, Historical Claims Duration, Year Eight	0.30%
Short-duration Insurance Contracts, Historical Claims Duration, Year Nine	0.20%
Short-duration Insurance Contracts, Historical Claims Duration, Year Ten	0.70%
Short-Duration Insurance Contracts, Historical Claims Duration, Net	98.60%
General Liability | Commercial
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Short-duration Insurance Contracts, Historical Claims Duration, Year One	4.30%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	15.90%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	19.50%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	20.50%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	15.70%
Short-duration Insurance Contracts, Historical Claims Duration, Year Six	8.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Seven	5.60%
Short-duration Insurance Contracts, Historical Claims Duration, Year Eight	3.20%
Short-duration Insurance Contracts, Historical Claims Duration, Year Nine	1.60%
Short-duration Insurance Contracts, Historical Claims Duration, Year Ten	0.80%
Short-Duration Insurance Contracts, Historical Claims Duration, Net	95.10%
Workers' Compensation | Commercial
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Short-duration Insurance Contracts, Historical Claims Duration, Year One	13.70%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	21.10%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	13.90%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	10.60%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	7.50%
Short-duration Insurance Contracts, Historical Claims Duration, Year Six	4.40%
Short-duration Insurance Contracts, Historical Claims Duration, Year Seven	4.40%
Short-duration Insurance Contracts, Historical Claims Duration, Year Eight	3.20%
Short-duration Insurance Contracts, Historical Claims Duration, Year Nine	2.50%
Short-duration Insurance Contracts, Historical Claims Duration, Year Ten	1.20%
Short-Duration Insurance Contracts, Historical Claims Duration, Net	82.50%
Excluding Hardy | International
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Short-duration Insurance Contracts, Historical Claims Duration, Year One	20.50%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	26.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	11.20%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	7.10%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	6.50%
Short-duration Insurance Contracts, Historical Claims Duration, Year Six	4.80%
Short-duration Insurance Contracts, Historical Claims Duration, Year Seven	4.30%
Short-duration Insurance Contracts, Historical Claims Duration, Year Eight	2.80%
Short-duration Insurance Contracts, Historical Claims Duration, Year Nine	1.70%
Short-duration Insurance Contracts, Historical Claims Duration, Year Ten	3.70%
Short-Duration Insurance Contracts, Historical Claims Duration, Net	88.60%
Hardy | International
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Short-duration Insurance Contracts, Historical Claims Duration, Year One	24.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	38.90%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	13.30%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	6.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	2.90%
Short-duration Insurance Contracts, Historical Claims Duration, Year Six	2.10%
Short-Duration Insurance Contracts, Historical Claims Duration, Net	87.20%

Claim and Claim Adjustment E_39

Claim and Claim Adjustment Expense Reserves (Impact of Loss Portfolio Transfer on the Consolidated Statement of Operations) (Details) - Asbestos and Environmental Reserves - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Liability for Claims and Claims Adjustment Expense [Line Items]
Net A&EP adverse development before consideration of LPT	$ 178	$ 60	$ 200
Provision for uncollectible third-party reinsurance on A&EP	(16)	0	0
Total additional amounts ceded under LPT	162	60	200
Retroactive reinsurance benefit recognized	(114)	(68)	(107)
Pretax impact of deferred retroactive reinsurance	$ 48	$ (8)	$ 93

Legal Proceedings, Contingenc_2

Legal Proceedings, Contingencies and Guarantees (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Guarantee Obligations
Legal Proceedings, Commitments and Contingencies, and Guarantees [Line Items]
Guarantor obligations, maximum exposure, undiscounted	$ 1,800
Indemnification Agreement
Legal Proceedings, Commitments and Contingencies, and Guarantees [Line Items]
Guarantor obligations, maximum exposure, undiscounted	252
Guarantee agreement
Legal Proceedings, Commitments and Contingencies, and Guarantees [Line Items]
Guarantor obligations, maximum exposure, undiscounted	375
Guarantee and Indemnification
Legal Proceedings, Commitments and Contingencies, and Guarantees [Line Items]
Guarantor obligations, current carrying calue	5	$ 5
Earned Premiums, Net | Insurance Premium Rate Adjustment | Multi-Peril Package Product
Legal Proceedings, Commitments and Contingencies, and Guarantees [Line Items]
Loss contingency accrual, period increase (decrease)	6	(36)	$ (16)
Interest Expense | Insurance Premium Rate Adjustment | Multi-Peril Package Product
Legal Proceedings, Commitments and Contingencies, and Guarantees [Line Items]
Loss contingency accrual, provision	$ 1	$ 7

Reinsurance (Narrative) (Detail

Reinsurance (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Ceded Credit Risk [Line Items]
Funds held under reinsurance agreements, liability	$ 3,200	$ 2,900
Reinsurance recoveries reported in insurance claims and policyholders' benefits reported on the Consolidated Statement of Operations	2,836	3,085	$ 3,016
Subsidiaries of Berkshire Hathaway Group
Ceded Credit Risk [Line Items]
Largest recoverables from single reinsurer	2,200
Gateway Rivers Insurance Company
Ceded Credit Risk [Line Items]
Largest recoverables from single reinsurer	278
Subsidiaries of Wilton Re
Ceded Credit Risk [Line Items]
Largest recoverables from single reinsurer	233
Significant Captive Program
Ceded Credit Risk [Line Items]
Direct and ceded earned premiums	3,740	3,864	3,865
Reinsurance recoveries reported in insurance claims and policyholders' benefits reported on the Consolidated Statement of Operations	$ 1,927	$ 2,541	$ 2,621

Reinsurance (Components of Rein

Reinsurance (Components of Reinsurance Receivables) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reinsurance receivables related to insurance reserves
Ceded claim and claim adjustment expenses	$ 4,019	$ 3,934	$ 4,094	$ 4,087
Ceded future policy benefits	233	230
Reinsurance receivables related to paid losses	203	126
Reinsurance receivables	4,455	4,290
Allowance for uncollectible reinsurance	(29)	(29)
Reinsurance receivables, net of allowance for uncollectible reinsurance	$ 4,426	$ 4,261

Reinsurance (Components of Earn

Reinsurance (Components of Earned Premiums) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Effects of Reinsurance [Line Items]
Direct premiums earned	$ 11,337	$ 10,936	$ 10,886
Assumed premiums earned	355	367	308
Ceded premiums earned	4,380	4,315	4,270
Net earned premiums	7,312	6,988	6,924
Property and Casualty Insurance
Effects of Reinsurance [Line Items]
Direct premiums earned	10,857	10,447	10,400
Assumed premiums earned	305	317	258
Ceded premiums earned	4,380	4,315	4,270
Net earned premiums	6,782	6,449	6,388
Long term care Insurance Product Line
Effects of Reinsurance [Line Items]
Direct premiums earned	480	489	486
Assumed premiums earned	50	50	50
Ceded premiums earned	0	0	0
Net earned premiums	$ 530	$ 539	$ 536
Percentage of assumed premiums earned to net premiums earned
Effects of Reinsurance [Line Items]
Percentage of assumed premium earned to premium earned net	4.90%	5.30%	4.40%
Percentage of assumed premiums earned to net premiums earned | Property and Casualty Insurance
Effects of Reinsurance [Line Items]
Percentage of assumed premium earned to premium earned net	4.50%	4.90%	4.00%
Percentage of assumed premiums earned to net premiums earned | Long term care Insurance Product Line
Effects of Reinsurance [Line Items]
Percentage of assumed premium earned to premium earned net	9.40%	9.30%	9.30%

Reinsurance (Components of Writ

Reinsurance (Components of Written Premiums) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Effects of Reinsurance [Line Items]
Direct premiums written	$ 11,568	$ 11,141	$ 10,946
Assumed premiums written	360	377	297
Ceded premiums written	4,583	4,449	4,255
Net written premiums	7,345	7,069	6,988
Property and Casualty Insurance
Effects of Reinsurance [Line Items]
Direct premiums written	11,094	10,655	10,451
Assumed premiums written	310	327	245
Ceded premiums written	4,583	4,449	4,255
Net written premiums	6,821	6,533	6,441
Long term care Insurance Product Line
Effects of Reinsurance [Line Items]
Direct premiums written	474	486	495
Assumed premiums written	50	50	52
Ceded premiums written	0	0	0
Net written premiums	$ 524	$ 536	$ 547
Percentage of assumed premiums written to net premiums written
Effects of Reinsurance [Line Items]
Percentage of assumed premium written to premium written net	4.90%	5.30%	4.30%
Percentage of assumed premiums written to net premiums written | Property and Casualty Insurance
Effects of Reinsurance [Line Items]
Percentage of assumed premium written to premium written net	4.50%	5.00%	3.80%
Percentage of assumed premiums written to net premiums written | Long term care Insurance Product Line
Effects of Reinsurance [Line Items]
Percentage of assumed premium written to premium written net	9.50%	9.30%	9.50%

Debt (Narrative) (Details)

Debt (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Debt Disclosure [Abstract]
Federal Home Loan Bank stock	$ 5,000,000
Federal Home Loan Bank, advances, general debt obligations, maximum amount available	111,000,000
Federal Home Loan Bank, advances, branch of FHLB Bank, amount of advances	$ 0	$ 0
Debt instrument, term	5 years
Line of credit, current borrowing capacity	$ 250,000,000
Line of credit, minimum net worth required for compliance	8,700,000,000
Line of credit, amount outstanding	$ 0	$ 0

Debt (Schedule of debt instrume

Debt (Schedule of debt instruments) (Details) - USD ($)	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Long term debt	$ 2,680,000,000		$ 2,708,000,000
Total	$ 2,680,000,000		2,858,000,000
5.875%, face amount of $500, due August 15, 2020
Debt Instrument [Line Items]
Stated interest rate	5.875%
Face amount	$ 500,000,000
Long term debt	$ 499,000,000		498,000,000
5.750%, face amount of $400, due August 15, 2021
Debt Instrument [Line Items]
Stated interest rate	5.75%
Face amount	$ 400,000,000
Long term debt	$ 399,000,000		398,000,000
3.950%, face amount of $550, due May 15, 2024
Debt Instrument [Line Items]
Stated interest rate	3.95%
Face amount	$ 550,000,000
Long term debt	$ 547,000,000		547,000,000
4.500%, face amount of $500, due March 1, 2026
Debt Instrument [Line Items]
Stated interest rate	4.50%
Face amount	$ 500,000,000
Long term debt	$ 498,000,000		498,000,000
3.450%, face amount of $500, due August 15, 2027
Debt Instrument [Line Items]
Stated interest rate	3.45%
Face amount	$ 500,000,000
Long term debt	$ 495,000,000		495,000,000
Debenture of CNAF, 7.250%, face amount of $243, due November 15, 2023
Debt Instrument [Line Items]
Stated interest rate	7.25%
Face amount	$ 243,000,000
Long term debt	242,000,000		242,000,000
Subordinated variable rate debt of Hardy, face amount of $30, due September 15, 2036(1)
Debt Instrument [Line Items]
Face amount	30,000,000
Long term debt	$ 0		30,000,000
Debt instrument, redemption amount		$ 30,000,000
Senior notes 6.950%, face amount $150, due January 15, 2018 [Member]
Debt Instrument [Line Items]
Stated interest rate	6.95%
Face amount	$ 150,000,000
Short term debt	$ 0		$ 150,000,000

Debt (Maturity of debt) (Detail

Debt (Maturity of debt) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Debt Disclosure [Abstract]
2,019	$ 0
2,020	500
2,021	400
2,022	0
2,023	243
Thereafter	1,550
Less discount	(13)
Total	$ 2,680	$ 2,858

Benefit Plans (Narrative) (Deta

Benefit Plans (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Percentage of limited partnerships employing hedge fund strategies focused on fixed income and equity investments	65.00%	71.00%
Assumptions used in calculating assumed health care cost trend rate	4.00%
Future capital call commitments for limited partnership investments	$ 574
Defined contribution plan, maximum annual contributions per employee, percent	50.00%
Defined contribution plan, employer matching contribution, percent of match	70.00%
Defined contribution plan, employer matching contribution, percent of employees' gross pay	6.00%
Defined contribution plan, employers matching contribution, vesting period in years	5 years
Benefit expense for the Company's savings plan	$ 71	$ 76	$ 75
Additional Contribution, Management Discretion
Defined contribution plan, employer matching contribution, percent of match	80.00%
Defined contribution plan, employer matching contribution, percent of employees' gross pay	6.00%
Defined contribution plan, employer discretionary contribution amount, percent	2.00%
First Year of Employment
Defined contribution plan, employer matching contribution, percent of match	35.00%
Defined contribution plan, employer matching contribution, percent of employees' gross pay	6.00%
Pension Benefits
Percentage of limited partnerships employing hedge fund strategies focused on fixed income and equity investments	81.00%	85.00%
Defined benefit plan, accumulated benefit obligation	$ 2,465	$ 2,749
Actuarial (gain) loss	(187)	99
Total non-service cost (benefit)	(23)	(7)	(10)
Future capital call commitments for limited partnership investments	$ 93
Limited partnership equity related hedge fund strategy plan assets	66.00%
Limited partnership hedge fund multi strategy plan assets	28.00%
Limited partnership hedge fund strategy distressed investments plan assets	6.00%
Defined benefit plan, expected future employer contributions, next fiscal year	$ 8
Postretirement Benefits
Actuarial (gain) loss	0	(1)
Total non-service cost (benefit)	$ (2)	$ (2)	$ (2)
Defined benefit plan, health care cost trend rate assumed for next fiscal year	4.00%	4.00%	4.00%
Defined benefit plan, expected future employer contributions, next fiscal year	$ 2
Minimum
Defined benefit plan, plan assets, target allocation, percentage	40.00%
Company contribution of eligible compensation, depending on age, percent	3.00%
Maximum
Defined benefit plan, plan assets, target allocation, percentage	60.00%
Company contribution of eligible compensation, depending on age, percent	5.00%
Insurance Claims and Policyholder's Benefits, Including Policyholder's Dividends | Pension Benefits
Total non-service cost (benefit)	$ (8)	$ (2)	$ (3)
Insurance Claims and Policyholder's Benefits, Including Policyholder's Dividends | Postretirement Benefits
Total non-service cost (benefit)	(1)	(1)	(1)
Other Expense | Pension Benefits
Total non-service cost (benefit)	(15)	(5)	(7)
Other Expense | Postretirement Benefits
Total non-service cost (benefit)	$ (1)	$ (1)	$ (1)

Benefit Plans (Funded Status) (

Benefit Plans (Funded Status) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Change in plan assets:
Balance beginning of period	$ 2,261
Balance end of period	2,025	$ 2,261
Pension Benefits
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Balance at beginning of period	2,749	2,729
Service cost	0	0	$ 0
Interest cost	93	103	113
Participants' contributions	0	0
Actuarial (gain) loss	(187)	99
Benefits paid	(166)	(170)
Foreign currency translation and other	(7)	10
Settlements	(16)	(22)
Balance at end of period	2,466	2,749	2,729
Change in plan assets:
Balance beginning of period	2,261	2,193
Actual return on plan assets	(69)	221
Company contributions	23	29
Participants' contributions	0	0
Benefits paid	(166)	(170)
Foreign currency translation and other	(8)	10
Settlements	(16)	(22)
Balance end of period	2,025	2,261	2,193
Defined Benefit Plan, Funded (Unfunded) Status of Plan [Abstract]
Funded status	(441)	(488)
Amounts recognized on the Consolidated Balance Sheets as of December 31:
Other assets	9	4
Other liabilities	(450)	(492)
Net amount recognized	(441)	(488)
Amounts recognized in Accumulated other comprehensive income, not yet recognized in net periodic cost (benefit):
Prior service credit	0	0
Net actuarial (gain) loss	984	987
Net amount recognized	984	987
Postretirement Benefits
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Balance at beginning of period	11	15
Service cost	0	0	0
Interest cost	0	0
Participants' contributions	3	4
Actuarial (gain) loss	0	(1)
Benefits paid	(5)	(7)
Foreign currency translation and other	0	0
Settlements	0	0
Balance at end of period	9	11	15
Change in plan assets:
Balance beginning of period	0	0
Actual return on plan assets	0	0
Company contributions	2	3
Participants' contributions	3	4
Benefits paid	(5)	(7)
Foreign currency translation and other	0	0
Settlements	0	0
Balance end of period	0	0	$ 0
Defined Benefit Plan, Funded (Unfunded) Status of Plan [Abstract]
Funded status	(9)	(11)
Amounts recognized on the Consolidated Balance Sheets as of December 31:
Other assets	0	0
Other liabilities	(9)	(11)
Net amount recognized	(9)	(11)
Amounts recognized in Accumulated other comprehensive income, not yet recognized in net periodic cost (benefit):
Prior service credit	0	(2)
Net actuarial (gain) loss	(3)	(4)
Net amount recognized	$ (3)	$ (6)

Benefit Plans (Components of ne

Benefit Plans (Components of net periodic cost (benefit)) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0	$ 0	$ 0
Interest cost on projected benefit obligation	93	103	113
Expected return on plan assets	(159)	(154)	(160)
Amortization of net actuarial (gain) loss	37	35	37
Settlement loss	6	9	0
Total non-service cost (benefit)	(23)	(7)	(10)
Total net periodic pension cost (benefit)	(23)	(7)	(10)
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0
Interest cost on projected benefit obligation	0	0
Amortization of prior service credit	(1)	(2)	(2)
Amortization of net actuarial (gain) loss	(1)	0	0
Total non-service cost (benefit)	(2)	(2)	(2)
Total net periodic pension cost (benefit)	$ (2)	$ (2)	$ (2)

Benefit Plans (Schedule of amou

Benefit Plans (Schedule of amounts recognized in Other comprehensive income) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Retirement Benefits [Abstract]
Amounts arising during the period	$ (41)	$ (31)	$ (29)
Settlement	6	9	(2)
Reclassification adjustment relating to prior service credit	(2)	(2)	(2)
Reclassification adjustment relating to actuarial loss	36	35	37
Total increase (decrease) in Other comprehensive income	$ (1)	$ 11	$ 4

Benefit Plans (Actuarial Assump

Benefit Plans (Actuarial Assumptions for Benefit Obligations) (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Interest crediting rate	5.00%	5.00%	5.00%
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Discount rate	4.25%	3.55%
Expected long term rate of return	7.50%	7.50%
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.55%	2.75%

Benefit Plans (Actuarial Assu_2

Benefit Plans (Actuarial Assumptions for Net Cost or Benefit) (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Interest crediting rate	5.00%	5.00%	5.00%
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.55%	3.95%	4.15%
Expected long term rate of return	7.50%	7.50%	7.50%
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Discount rate	2.75%	2.75%	2.75%

Benefit Plans (Fair Value of Pl

Benefit Plans (Fair Value of Plan Assets Measured on a Recurring Basis) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 2,025	$ 2,261
Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,236	1,357
Total limited partnerships measured at net asset value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	789	904
Corporate and other bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	482	532
Corporate and other bonds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Corporate and other bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	472	522
Corporate and other bonds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	10	10
States, municipalities and political subdivisions
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	58	62
States, municipalities and political subdivisions | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
States, municipalities and political subdivisions | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	58	62
States, municipalities and political subdivisions | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Asset-backed
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	165	180
Asset-backed | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Asset-backed | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	165	180
Asset-backed | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Total fixed maturity securities trading
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	705	774
Total fixed maturity securities trading | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Total fixed maturity securities trading | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	695	764
Total fixed maturity securities trading | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	10	10
Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	441
Equity securities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	331
Equity securities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	110
Equity securities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0
Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		527
Equity securities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		405
Equity securities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		122
Equity securities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0
Short term investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	81	34
Short term investments | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	27	23
Short term investments | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	54	11
Short term investments | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other assets
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	9	9
Other assets | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other assets | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	9	9
Other assets | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Cash
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		13
Cash | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		13
Cash | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0
Cash | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0
Total assets measured at fair value | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	358	441
Total assets measured at fair value | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	868	906
Total assets measured at fair value | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 10	$ 10

Benefit Plans (Estimated Future

Benefit Plans (Estimated Future Minimum Benefit Payments to Participants) (Details) $ in Millions	Dec. 31, 2018USD ($)
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
2,019	$ 175
2,020	174
2,021	175
2,022	177
2,023	177
2024-2028	850
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
2,019	2
2,020	2
2,021	1
2,022	1
2,023	1
2024-2028	$ 2

Stock-Based Compensation (Narra

Stock-Based Compensation (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized	11,000,000
Number of shares available for grant	1,800,000
Allocated share-based compensation expense	$ 32	$ 36	$ 36
Tax benefit from compensation expense	8	18	12
Compensation cost not yet recognized	$ 44
Compensation cost not yet recognized, period for recognition	1 year 8 months 12 days
Share-based compensation arrangement by share-based payment award, equity instruments other than options, vested in period, fair value	$ 16	$ 34	$ 12
Weighted average grant date fair value of awards granted (in usd per share)	$ 51.64	$ 44.20	$ 32.27
Performance Based Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	4 years
Performance Shares | Annual Performance Share Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Measurement period of specific annual performance goals, in years	1 year
Cliff vesting period following date of grant	2 years
Performance Shares | Long Term Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Measurement period of specific annual performance goals, in years	3 years
Performance Shares | Special Supplemental Equity Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Service based vesting period	2 years
Minimum | Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	2 years
Minimum | Performance Based Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting rights, percentage	0.00%
Minimum | Performance Shares | Annual Performance Share Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting rights, percentage	0.00%
Minimum | Performance Shares | Long Term Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting rights, percentage	0.00%
Maximum | Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	3 years
Maximum | Performance Based Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting rights, percentage	100.00%
Maximum | Performance Shares | Annual Performance Share Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting rights, percentage	200.00%
Maximum | Performance Shares | Long Term Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting rights, percentage	200.00%

Stock-Based Compensation (Restr

Stock-Based Compensation (Restricted shares, performance-based restricted share units and performance share unit activity) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Number of Awards
Number of nonvested awards, beginning of period (in shares)	2,070,737
Number of awards granted (in shares)	840,961
Number of awards vested (in shares)	(463,725)
Number of awards forfeited, canceled or expired (in shares)	(307,719)
Performance-based adjustment (in shares)	63,894
Number of nonvested awards, end of period (in shares)	2,204,148	2,070,737
Weighted-Average Grant Date Fair Value
Weighted average grant date fair value of nonvested awards, beginning of period (in usd per share)	$ 38.92
Weighted average grant date fair value of awards granted (in usd per share)	51.64	$ 44.20	$ 32.27
Weighted average grant date fair value of awards vested (in usd per share)	38.62
Weighted average grant date fair value of awards forfeited, canceled or expired (in usd per share)	40.59
Weighted average grant date fair value of performance based adjustment (in usd per share)	52
Weighted average grant date fair value of nonvested awards, end of period (in usd per share)	$ 43.98	$ 38.92

Other Intangible Assets (Summar

Other Intangible Assets (Summary of Other Intangible Assets) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Schedule of Other Intangible Assets [Abstract]
Finite-lived intangible assets	$ 16	$ 18
Intangible Assets, Gross (Excluding Goodwill)	77	81
Indefinite-lived intangible assets	61	63
Accumulated amortization	9	9
Syndicate capacity
Schedule of Other Intangible Assets [Abstract]
Indefinite-lived intangible assets	45	47
Agency force
Schedule of Other Intangible Assets [Abstract]
Indefinite-lived intangible assets	$ 16	16
Trade Names
Schedule of Other Intangible Assets [Abstract]
Economic useful life measured in years	8 years
Finite-lived intangible assets	$ 6	7
Accumulated amortization	$ 5	5
Distribution channel
Schedule of Other Intangible Assets [Abstract]
Economic useful life measured in years	15 years
Finite-lived intangible assets	$ 10	11
Accumulated amortization	$ 4	$ 4

Schedule of Other Intangible As

Schedule of Other Intangible Assets (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
2,019	$ 1
2,020	1
2,021	1
2,022	1
2,023	1
Other Intangible Assets | International
Finite-Lived Intangible Assets [Line Items]
Amortization expense included in other operating expenses	$ 1	$ 2	$ 1

Operating Leases (Narrative) (D

Operating Leases (Narrative) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Leases, Operating [Abstract]
Rent expense	$ 62	$ 66	$ 60

Operating Leases (Future Minimu

Operating Leases (Future Minimum Lease Payments) (Details) $ in Millions	Dec. 31, 2018USD ($)
Leases, Operating [Abstract]
2,019	$ 35
2,020	39
2,021	41
2,022	38
2,023	32
Thereafter	200
Total	$ 385

Stockholders' Equity and Stat_3

Stockholders' Equity and Statutory Accounting Practices (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Stockholders' Equity and Statutory Accounting Practices [Abstract]
Increase in statutory capital and surplus due to prescribed practice	$ 88	$ 63
Statutory amount available for dividend payment before consideration of statutory dividends paid in the preceding twelve months	1,383
Dividends paid in the preceding twelve months	$ 1,026
Capital required for capital adequacy to risk weighted assets	266.00%	264.00%

Stockholders' Equity and Stat_4

Stockholders' Equity and Statutory Accounting Practices Combined statutory capital and surplus and net income (loss) (Details) - Combined Continental Casualty Companies - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statutory Accounting Practices [Line Items]
Statutory Capital and Surplus	$ 10,411	$ 10,726
Statutory Net Income (Loss)	$ 1,405	$ 1,029	$ 1,033

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Income (Loss) by Component Schedule of Accumulated Other Comprehensive Income (Loss) by Component (Details) - USD ($) $ in Millions	Jan. 01, 2018	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2017	Jan. 01, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period	$ 12,244	$ 12,244	$ 11,969
Other comprehensive income (loss) before reclassifications		(922)	262
Amounts reclassified from accumulated other comprehensive income (loss) net of tax		(28)	57
Other comprehensive income (loss) after tax (expense) benefit		(894)	205
Total stockholder's equity at end of period		11,217	12,244
Reclassification from AOCI, tax		8	24
Tax (expense) benefit on other comprehensive income (loss)		216	(75)
Net unrealized gains (losses) on investments with OTTI losses
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period	25	25	30
Total stockholders equity, adjusted balance	30
Other comprehensive income (loss) before reclassifications		(7)	(3)
Amounts reclassified from accumulated other comprehensive income (loss) net of tax		7	2
Other comprehensive income (loss) after tax (expense) benefit		(14)	(5)
Total stockholder's equity at end of period		16	25
Reclassification from AOCI, tax		(2)	1
Tax (expense) benefit on other comprehensive income (loss)		4	2
Net unrealized gains (losses) on other investments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period	750	750	642
Total stockholders equity, adjusted balance	859
Other comprehensive income (loss) before reclassifications		(801)	190
Amounts reclassified from accumulated other comprehensive income (loss) net of tax		(3)	82
Other comprehensive income (loss) after tax (expense) benefit		(798)	108
Total stockholder's equity at end of period		61	750
Reclassification from AOCI, tax		2	38
Tax (expense) benefit on other comprehensive income (loss)		211	(68)
Pension and postretirement benefits
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period	(645)	(645)	(647)
Total stockholders equity, adjusted balance	(775)
Other comprehensive income (loss) before reclassifications		(32)	(25)
Amounts reclassified from accumulated other comprehensive income (loss) net of tax		(32)	(27)
Other comprehensive income (loss) after tax (expense) benefit		0	2
Total stockholder's equity at end of period		(775)	(645)
Reclassification from AOCI, tax		8	(15)
Tax (expense) benefit on other comprehensive income (loss)		1	(9)
Cumulative foreign currency translation adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period	(98)	(98)	(198)
Total stockholders equity, adjusted balance	(98)
Other comprehensive income (loss) before reclassifications		(82)	100
Amounts reclassified from accumulated other comprehensive income (loss) net of tax		0	0
Other comprehensive income (loss) after tax (expense) benefit		(82)	100
Total stockholder's equity at end of period		(180)	(98)
Reclassification from AOCI, tax		0	0
Tax (expense) benefit on other comprehensive income (loss)		0	0
Accumulated other comprehensive income (loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period	32	32	(173)
Cumulative effect adjustments from changes in accounting guidance, net of tax	(16)			$ 0	$ 0
Total stockholders equity, adjusted balance	16
Total stockholder's equity at end of period	16	$ (878)	$ 32
ASU 2018-02
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cumulative effect adjustments from changes in accounting guidance, net of tax	12
ASU 2018-02 | Net unrealized gains (losses) on investments with OTTI losses
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cumulative effect adjustments from changes in accounting guidance, net of tax	5
ASU 2018-02 | Net unrealized gains (losses) on other investments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cumulative effect adjustments from changes in accounting guidance, net of tax	137
ASU 2018-02 | Pension and postretirement benefits
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cumulative effect adjustments from changes in accounting guidance, net of tax	(130)
ASU 2018-02 | Cumulative foreign currency translation adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cumulative effect adjustments from changes in accounting guidance, net of tax	0
ASU 2018-02 | Accumulated other comprehensive income (loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cumulative effect adjustments from changes in accounting guidance, net of tax	12
ASU 2016-01
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cumulative effect adjustments from changes in accounting guidance, net of tax	(28)
Cumulative effect, Tax	8
ASU 2016-01 | Net unrealized gains (losses) on investments with OTTI losses
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cumulative effect adjustments from changes in accounting guidance, net of tax	0
Cumulative effect, Tax	0
ASU 2016-01 | Net unrealized gains (losses) on other investments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cumulative effect adjustments from changes in accounting guidance, net of tax	(28)
Cumulative effect, Tax	8
ASU 2016-01 | Pension and postretirement benefits
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cumulative effect adjustments from changes in accounting guidance, net of tax	0
Cumulative effect, Tax	0
ASU 2016-01 | Cumulative foreign currency translation adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cumulative effect adjustments from changes in accounting guidance, net of tax	0
Cumulative effect, Tax	$ 0

Business Segments (Narrative) (

Business Segments (Narrative) (Details) - segments	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Percentage of direct foreign written premiums	9.30%	7.70%	7.90%
Core Segments - Specialty, Commercial and International
Segment Reporting Information [Line Items]
Number of operating segments	3
Non-Core Segments, Life & Group Non-Core and Corporate and Other Non-Core
Segment Reporting Information [Line Items]
Number of operating segments	2

Business Segments (Income State

Business Segments (Income Statement Information) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Net written premiums	$ 7,345	$ 7,069	$ 6,988
Operating revenues
Net earned premiums	7,312	6,988	6,924
Net investment income	1,817	2,034	1,988
Non-insurance warranty revenue	1,007	390	361
Other revenues	50	37	43
Total operating revenues	10,186	9,449	9,316
Claims, Benefits and Expenses
Net incurred claims and benefits	5,547	5,288	5,270
Policyholders’ dividends	25	22	13
Amortization of deferred acquisition costs	1,335	1,233	1,235
Non-insurance warranty expense	923	299	271
Other insurance related expenses	1,039	1,098	1,122
Other expenses	301	292	318
Total claims, benefits and expenses	9,170	8,232	8,229
Core income (loss) before income tax	1,016	1,217	1,087
Income tax (expense) benefit on core income (loss)	(171)	(298)	(263)
Core income (loss)	845	919	824
Net realized investment gains (losses)	(52)	93	50
Income tax (expense) benefit on net realized investment gains (losses)	14	(30)	(15)
Net realized investment gains (losses), after tax	(38)	63	35
Net deferred tax asset remeasurement	6	(83)
Net income	813	899	859
Operating Segments | Specialty
Segment Reporting Information [Line Items]
Net written premiums	2,744	2,731	2,738
Operating revenues
Net earned premiums	2,732	2,712	2,743
Net investment income	439	522	497
Non-insurance warranty revenue	1,007	390	361
Other revenues	2	1	1
Total operating revenues	4,180	3,625	3,602
Claims, Benefits and Expenses
Net incurred claims and benefits	1,526	1,533	1,489
Policyholders’ dividends	5	4	4
Amortization of deferred acquisition costs	599	590	586
Non-insurance warranty expense	923	299	271
Other insurance related expenses	279	279	295
Other expenses	46	43	41
Total claims, benefits and expenses	3,378	2,748	2,686
Core income (loss) before income tax	802	877	916
Income tax (expense) benefit on core income (loss)	(173)	(295)	(310)
Core income (loss)	629	582	606
Operating Segments | Commercial
Segment Reporting Information [Line Items]
Net written premiums	3,060	2,922	2,883
Operating revenues
Net earned premiums	3,050	2,881	2,840
Net investment income	500	658	657
Non-insurance warranty revenue	0	0	0
Other revenues	28	32	32
Total operating revenues	3,578	3,571	3,529
Claims, Benefits and Expenses
Net incurred claims and benefits	2,053	1,930	1,905
Policyholders’ dividends	20	18	9
Amortization of deferred acquisition costs	505	481	475
Non-insurance warranty expense	0	0	0
Other insurance related expenses	505	530	566
Other expenses	43	57	36
Total claims, benefits and expenses	3,126	3,016	2,991
Core income (loss) before income tax	452	555	538
Income tax (expense) benefit on core income (loss)	(95)	(186)	(183)
Core income (loss)	357	369	355
Operating Segments | International
Segment Reporting Information [Line Items]
Net written premiums	1,018	881	821
Operating revenues
Net earned premiums	1,001	857	806
Net investment income	57	52	51
Non-insurance warranty revenue	0	0	0
Other revenues	1	0	0
Total operating revenues	1,059	909	857
Claims, Benefits and Expenses
Net incurred claims and benefits	699	575	492
Policyholders’ dividends	0	0	0
Amortization of deferred acquisition costs	231	162	174
Non-insurance warranty expense	0	0	0
Other insurance related expenses	135	162	133
Other expenses	14	(7)	24
Total claims, benefits and expenses	1,079	892	823
Core income (loss) before income tax	(20)	17	34
Income tax (expense) benefit on core income (loss)	1	(9)	(13)
Core income (loss)	(19)	8	21
Operating Segments | Life & Group
Segment Reporting Information [Line Items]
Net written premiums	524	536	547
Operating revenues
Net earned premiums	530	539	536
Net investment income	801	782	767
Non-insurance warranty revenue	0	0	0
Other revenues	2	2	(2)
Total operating revenues	1,333	1,323	1,301
Claims, Benefits and Expenses
Net incurred claims and benefits	1,218	1,269	1,286
Policyholders’ dividends	0	0	0
Amortization of deferred acquisition costs	0	0	0
Non-insurance warranty expense	0	0	0
Other insurance related expenses	122	129	132
Other expenses	7	7	8
Total claims, benefits and expenses	1,347	1,405	1,426
Core income (loss) before income tax	(14)	(82)	(125)
Income tax (expense) benefit on core income (loss)	57	132	145
Core income (loss)	43	50	20
Operating Segments | Corporate & Other
Segment Reporting Information [Line Items]
Net written premiums	0	0	0
Operating revenues
Net earned premiums	0	0	0
Net investment income	20	20	16
Non-insurance warranty revenue	0	0	0
Other revenues	19	2	12
Total operating revenues	39	22	28
Claims, Benefits and Expenses
Net incurred claims and benefits	51	(19)	98
Policyholders’ dividends	0	0	0
Amortization of deferred acquisition costs	0	0	0
Non-insurance warranty expense	0	0	0
Other insurance related expenses	(1)	(1)	(3)
Other expenses	193	192	209
Total claims, benefits and expenses	243	172	304
Core income (loss) before income tax	(204)	(150)	(276)
Income tax (expense) benefit on core income (loss)	39	60	98
Core income (loss)	(165)	(90)	(178)
Eliminations
Segment Reporting Information [Line Items]
Net written premiums	(1)	(1)	(1)
Operating revenues
Net earned premiums	(1)	(1)	(1)
Net investment income	0	0	0
Non-insurance warranty revenue	0	0	0
Other revenues	(2)	0	0
Total operating revenues	(3)	(1)	(1)
Claims, Benefits and Expenses
Net incurred claims and benefits	0	0	0
Policyholders’ dividends	0	0	0
Amortization of deferred acquisition costs	0	0	0
Non-insurance warranty expense	0	0	0
Other insurance related expenses	(1)	(1)	(1)
Other expenses	(2)	0	0
Total claims, benefits and expenses	(3)	(1)	(1)
Core income (loss) before income tax	0	0	0
Income tax (expense) benefit on core income (loss)	0	0	0
Core income (loss)	$ 0	$ 0	$ 0

Business Segments (Balance Shee

Business Segments (Balance Sheet Information) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Reinsurance receivables	$ 4,455		$ 4,290
Insurance receivables	2,365		2,336
Deferred acquisition costs	633		634
Goodwill	146		148
Deferred non-insurance warranty acquisition expense	2,513	$ 2,094	212
Insurance reserves
Claim and claim adjustment expenses	21,984		22,004
Unearned premiums	4,183		4,029
Future policy benefits	10,597		11,179
Deferred non-insurance warranty revenue	3,402	$ 2,941	972
Operating Segments | Specialty
Segment Reporting Information [Line Items]
Reinsurance receivables	649		671
Insurance receivables	947		969
Deferred acquisition costs	308		318
Goodwill	117		117
Deferred non-insurance warranty acquisition expense	2,513		212
Insurance reserves
Claim and claim adjustment expenses	5,465		5,669
Unearned premiums	2,132		2,020
Future policy benefits	0		0
Deferred non-insurance warranty revenue	3,402		972
Operating Segments | Commercial
Segment Reporting Information [Line Items]
Reinsurance receivables	795		654
Insurance receivables	1,277		1,103
Deferred acquisition costs	230		223
Goodwill	0		0
Deferred non-insurance warranty acquisition expense	0		0
Insurance reserves
Claim and claim adjustment expenses	8,743		8,764
Unearned premiums	1,454		1,409
Future policy benefits	0		0
Deferred non-insurance warranty revenue	0		0
Operating Segments | International
Segment Reporting Information [Line Items]
Reinsurance receivables	250		212
Insurance receivables	284		254
Deferred acquisition costs	95		93
Goodwill	29		31
Deferred non-insurance warranty acquisition expense	0		0
Insurance reserves
Claim and claim adjustment expenses	1,750		1,636
Unearned premiums	475		472
Future policy benefits	0		0
Deferred non-insurance warranty revenue	0		0
Operating Segments | Life & Group
Segment Reporting Information [Line Items]
Reinsurance receivables	414		438
Insurance receivables	9		8
Deferred acquisition costs	0		0
Goodwill	0		0
Deferred non-insurance warranty acquisition expense	0		0
Insurance reserves
Claim and claim adjustment expenses	3,601		3,499
Unearned premiums	122		128
Future policy benefits	10,597		11,179
Deferred non-insurance warranty revenue	0		0
Operating Segments | Corporate & Other
Segment Reporting Information [Line Items]
Reinsurance receivables	2,347		2,315
Insurance receivables	(152)		2
Deferred acquisition costs	0		0
Goodwill	0		0
Deferred non-insurance warranty acquisition expense	0		0
Insurance reserves
Claim and claim adjustment expenses	2,425		2,436
Unearned premiums	0		0
Future policy benefits	0		0
Deferred non-insurance warranty revenue	0		0
Eliminations
Segment Reporting Information [Line Items]
Reinsurance receivables	0		0
Insurance receivables	0		0
Deferred acquisition costs	0		0
Goodwill	0		0
Deferred non-insurance warranty acquisition expense	0		0
Insurance reserves
Claim and claim adjustment expenses	0		0
Unearned premiums	0		0
Future policy benefits	0		0
Deferred non-insurance warranty revenue	$ 0		$ 0

Business Segments (Revenues by

Business Segments (Revenues by Line of Business) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues	$ 2,403	$ 2,622	$ 2,574	$ 2,535	$ 2,448	$ 2,398	$ 2,366	$ 2,330	$ 10,134	$ 9,542	$ 9,366
Net realized investment gains (losses)									(52)	93	50
Operating Segments | Specialty
Revenues									4,180	3,625	3,602
Operating Segments | Commercial
Revenues									3,578	3,571	3,529
Operating Segments | International
Revenues									1,059	909	857
Operating Segments | Life & Group
Revenues									1,333	1,323	1,301
Operating Segments | Corporate & Other
Revenues									39	22	28
Eliminations
Revenues									(3)	(1)	(1)
Total operating revenues
Revenues									10,186	9,449	9,316
Management & Professional Liability | Operating Segments | Specialty
Revenues									2,440	2,533	2,562
Surety | Operating Segments | Specialty
Revenues									571	541	529
Warranty & Alternative Risks | Operating Segments | Specialty
Revenues									1,169	551	511
Middle Market | Operating Segments | Commercial
Revenues									2,045	1,965	1,823
Small Business | Operating Segments | Commercial
Revenues									472	480	582
Other Commercial Insurance | Operating Segments | Commercial
Revenues									1,061	1,126	1,124
Canada | Operating Segments | International
Revenues									255	224	203
Europe | Operating Segments | International
Revenues									363	326	314
Hardy | Operating Segments | International
Revenues									$ 441	$ 359	$ 340

Quarterly Financial Data (Una_3

Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Liability for Catastrophe Claims [Line Items]
Revenues	$ 2,403	$ 2,622	$ 2,574	$ 2,535	$ 2,448	$ 2,398	$ 2,366	$ 2,330	$ 10,134	$ 9,542	$ 9,366
Net income	$ (84)	$ 336	$ 270	$ 291	$ 223	$ 144	$ 272	$ 260	$ 813	$ 899	$ 859
Basic earnings (loss) per share (in usd per share)	$ (0.31)	$ 1.24	$ 0.99	$ 1.07	$ 0.82	$ 0.53	$ 1.01	$ 0.96	$ 2.99	$ 3.32	$ 3.18
Diluted earnings (loss) per share (in usd per share)	$ (0.31)	$ 1.23	$ 0.99	$ 1.07	$ 0.82	$ 0.53	$ 1	$ 0.96	$ 2.98	$ 3.30	$ 3.17
Net deferred tax asset remeasurement					$ 83
Hurricane Michael and California Wildfires
Liability for Catastrophe Claims [Line Items]
Catastrophe losses net of reinsurance	$ 107
Hurricane Harvey, Irma and Maria
Liability for Catastrophe Claims [Line Items]
Catastrophe losses net of reinsurance						$ 188
Limited Partnership and Common Stock Investments [Member]
Liability for Catastrophe Claims [Line Items]
Loss on limited partnership and common stock investments	$ 109

Related Party Transactions Narr

Related Party Transactions Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Due to related parties	$ 23	$ 143
Fees and expenses of investment facilities and services
Amounts reimbursed to Loews for services provided to the Company	43	43	$ 43
Due to related parties	23	22
Corporate services and related travel expenses
Amounts reimbursed to Loews for services provided to the Company	1	1
Taxes paid
Due to related parties	8	121
Loews
Amounts earned from Loews for insurance premiums	$ 2	$ 2	$ 2

Non-Insurance Revenues from C_2

Non-Insurance Revenues from Contracts with Customers (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred non-insurance warranty revenue	$ 3,402	$ 2,941	$ 972
Contract with customer, liability, revenue recognized	834
Deferred non-insurance warranty acquisition expense	2,513	$ 2,094	$ 212
Amortization of deferred sales commissions	673
Capitalized Commission Costs
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred non-insurance warranty acquisition expense	2,500
Capitalized Administrator Service Costs
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred non-insurance warranty acquisition expense	$ 24

Non-Insurance Revenues from C_3

Non-Insurance Revenues from Contracts with Customers (Performance Obligation) (Details) $ in Millions	Dec. 31, 2018USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Remaining performance obligation, amount	$ 963
Remaining performance obligation, expected timing of satisfaction, period	12 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Remaining performance obligation, amount	$ 791
Remaining performance obligation, expected timing of satisfaction, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Remaining performance obligation, amount	$ 613
Remaining performance obligation, expected timing of satisfaction, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Remaining performance obligation, amount	$ 1,000
Remaining performance obligation, expected timing of satisfaction, period

Schedule II. Condensed Financ_2

Schedule II. Condensed Financial Information of Registrant (Parent Company) (Schedule of Condensed Financial Information of Registrant, Statements of Operations and Comprehensive Income) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues
Net investment income									$ 1,817	$ 2,034	$ 1,988
Net realized investment gains (losses)									(52)	93	50
Total revenues	$ 2,403	$ 2,622	$ 2,574	$ 2,535	$ 2,448	$ 2,398	$ 2,366	$ 2,330	10,134	9,542	9,366
Expenses
Interest									138	161	159
Income tax expense									(151)	(411)	(278)
Net income	$ (84)	$ 336	$ 270	$ 291	$ 223	$ 144	$ 272	$ 260	813	899	859
Total comprehensive (loss) income									(81)	1,104	1,001
Parent Company
Revenues
Net investment income									10	6	3
Net realized investment gains (losses)									0	(42)	(7)
Total revenues									10	(36)	(4)
Expenses
Administrative and general									1	2	1
Interest									135	152	155
Total expenses									136	154	156
Loss from operations before income taxes and equity in net income of subsidiaries									(126)	(190)	(160)
Income tax expense									9	57	41
Loss before equity in net income of subsidiaries									(117)	(133)	(119)
Equity in net income of subsidiaries									930	1,032	978
Net income									813	899	859
Equity in other comprehensive income of subsidiaries									(894)	205	142
Total comprehensive (loss) income									$ (81)	$ 1,104	$ 1,001

Schedule II. Condensed Financ_3

Schedule II. Condensed Financial Information of Registrant (Parent Company) (Schedule of Condensed Financial Information of Registrant, Balance Sheets) (Details) - USD ($) $ / shares in Units, $ in Millions	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Assets
Cash	$ 310		$ 355	$ 271	$ 387
Short term investments	1,286		1,436
Other assets	1,208		921
Total assets	57,152		56,567
Liabilities
Short term debt	0		150
Long term debt	2,680		2,708
Other liabilities	3,089		3,281
Total liabilities	45,935		44,323
Stockholders' Equity
Common stock ($2.50 par value; 500,000,000 shares authorized; 273,040,243 shares issued; 271,456,978 and 271,205,390 shares outstanding)	683		683
Additional paid-in capital	2,192		2,175
Retained earnings	9,277	$ 9,348	9,414
Accumulated other comprehensive (loss) income	(878)		32
Treasury stock (1,583,265 and 1,834,853 shares), at cost	(57)		(60)
Total stockholders’ equity	11,217		12,244	11,969
Total liabilities and stockholders' equity	$ 57,152		$ 56,567
Balance Sheet Parenthetical
Common stock, par value (in usd per share)	$ 2.50		$ 2.50
Common stock, shares authorized (in shares	500,000,000		500,000,000
Common stock, shares issued (in shares)	273,040,243		273,040,243
Common stock, shares outstanding (in shares)	271,456,978		271,205,390
Treasury stock, shares (in shares)	1,583,265		1,834,853
Parent Company
Assets
Investment in subsidiaries	$ 13,427		$ 14,481
Cash	1		1	$ 1	$ 4
Short term investments	519		638
Amounts due from affiliates	2		4
Other assets	0		1
Total assets	13,949		15,125
Liabilities
Short term debt	0		150
Long term debt	2,680		2,678
Other liabilities	52		53
Total liabilities	2,732		2,881
Stockholders' Equity
Common stock ($2.50 par value; 500,000,000 shares authorized; 273,040,243 shares issued; 271,456,978 and 271,205,390 shares outstanding)	683		683
Additional paid-in capital	2,192		2,175
Retained earnings	9,277		9,414
Accumulated other comprehensive (loss) income	(878)		32
Treasury stock (1,583,265 and 1,834,853 shares), at cost	(57)		(60)
Total stockholders’ equity	11,217		12,244
Total liabilities and stockholders' equity	$ 13,949		$ 15,125

Schedule II. Condensed Financ_4

Schedule II. Condensed Financial Information of Registrant (Parent Company) (Schedule of Condensed Financial Information of Registrant, Statements of Cash Flows) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash Flows from Operating Activities
Net income	$ (84)	$ 336	$ 270	$ 291	$ 223	$ 144	$ 272	$ 260	$ 813	$ 899	$ 859
Adjustments to reconcile net income to net cash flows provided by operating activities:
Net realized investment gains (losses)									52	(93)	(50)
Other, net									67	38	29
Total adjustments									414	355	557
Net cash flows provided by operating activities									1,227	1,254	1,416
Cash Flows from Investing Activities
Change in short term investments									168	(6)	258
Other, net									18	20	2
Net cash flows used by investing activities									(177)	(424)	(846)
Cash Flows from Financing Activities
Dividends paid to common stockholders									(896)	(842)	(813)
Proceeds from the issuance of debt									0	496	498
Repayment of debt									(180)	(391)	(358)
Other, net									(9)	(18)	0
Net cash flows used by financing activities									(1,085)	(755)	(673)
Net change in cash									(45)	84	(116)
Cash, beginning of year				355				271	355	271	387
Cash, end of year	310				355				310	355	271
Parent Company
Cash Flows from Operating Activities
Net income									813	899	859
Adjustments to reconcile net income to net cash flows provided by operating activities:
Equity in net income of subsidiaries									(930)	(1,032)	(978)
Dividends received from subsidiaries									1,026	955	765
Net realized investment gains (losses)									0	42	7
Other, net									16	36	21
Total adjustments									112	1	(185)
Net cash flows provided by operating activities									925	900	674
Cash Flows from Investing Activities
Change in short term investments									130	(146)	(9)
Capital contributions to subsidiaries									(2)	0	0
Other, net									0	0	4
Net cash flows used by investing activities									128	(146)	(5)
Cash Flows from Financing Activities
Dividends paid to common stockholders									(896)	(842)	(813)
Proceeds from the issuance of debt									0	496	498
Repayment of debt									(150)	(391)	(358)
Other, net									(7)	(17)	1
Net cash flows used by financing activities									(1,053)	(754)	(672)
Net change in cash									0	0	(3)
Cash, beginning of year				$ 1				$ 1	1	1	4
Cash, end of year	$ 1				$ 1				$ 1	$ 1	$ 1

Schedule II. Condensed Financ_5

Schedule II. Condensed Financial Information of Registrant (Parent Company) (Narrative) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Parent Company
Condensed Financial Statements, Captions [Line Items]
Guarantor obligations, current carrying calue	$ 5	$ 5
Guarantor obligations, maximum exposure, undiscounted	$ 1,800
CNAF Consolidated | Loews
Condensed Financial Statements, Captions [Line Items]
Noncontrolling interest, ownership percentage by parent	89.00%
Indemnification Agreement
Condensed Financial Statements, Captions [Line Items]
Guarantor obligations, maximum exposure, undiscounted	$ 252
Indemnification Agreement | Parent Company
Condensed Financial Statements, Captions [Line Items]
Guarantor obligations, maximum exposure, undiscounted	$ 625

Schedule V. Valuation and Qua_2

Schedule V. Valuation and Qualifying Accounts (Schedule of valuation and qualifying accounts) (Details) - Allowance for doubtful accounts, insurance and reinsurance receivables - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Movement in valuation allowances and reserves [Roll Forward]
Balance at beginning of period	$ 73	$ 83	$ 89
Charged to Costs and Expenses	4	(1)	(2)
Charged to other accounts	0	0	(1)
Deductions	(6)	(9)	(3)
Balance at end of period	$ 71	$ 73	$ 83

Schedule VI. Supplemental Inf_2

Schedule VI. Supplemental Information Concerning Property and Casualty Insurance Operations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Incurred claim and claim adjustment expenses related to current year	$ 5,358	$ 5,201	$ 5,025
Incurred claim and claim adjustment expenses related to prior years	(179)	(381)	(342)
Consolidated Property and Casualty Insurance Entity
Deferred acquisition costs	632	632
Reserves for unpaid claim and claim adjustment expenses	21,984	22,004
Discount deducted from claim and claim adjustment expense reserves above (based on interest rates ranging from 3.5% to 8.0%)	1,388	1,434
Unearned premiums	4,183	4,029
Net written premiums	7,345	7,069	6,988
Net earned premiums	7,312	6,988	6,924
Net investment income	1,751	1,992	1,952
Incurred claim and claim adjustment expenses related to current year		5,201	5,025
Incurred claim and claim adjustment expenses related to prior years		(381)	(342)
Amortization of deferred acquisition costs	1,335	1,233	1,235
Paid claim and claim adjustment expenses	$ 5,331	$ 5,341	$ 5,134
Consolidated Property and Casualty Insurance Entity | Minimum
Supplemental Information Parenthetical
SEC Schedule, 12-18, supplemental information, property-casualty insurance underwriters, interest rate at which discount computed	3.50%	3.50%
Consolidated Property and Casualty Insurance Entity | Maximum
Supplemental Information Parenthetical
SEC Schedule, 12-18, supplemental information, property-casualty insurance underwriters, interest rate at which discount computed	8.00%	8.00%

Uncategorized Items - cna-20181

Label	Element	Value
AOCI Attributable to Parent [Member]
Stockholders' Equity Attributable to Parent	us-gaap_StockholdersEquity	$ (315,000,000)
Stockholders' Equity Attributable to Parent	us-gaap_StockholdersEquity	(173,000,000)
Retained Earnings [Member]
Stockholders' Equity Attributable to Parent	us-gaap_StockholdersEquity	9,313,000,000
Stockholders' Equity Attributable to Parent	us-gaap_StockholdersEquity	9,359,000,000
Stockholders' Equity Attributable to Parent	us-gaap_StockholdersEquity	$ 9,364,000,000