Debt - Schedule of Long-Term Debt Instruments (Detail) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Debt, Gross	$ 11,488	$ 11,653
Less unamortized discount and issuance costs	112	120
Debt	11,376	11,533
Loews Corporation [Member]
Debt Instrument [Line Items]
Debt, Gross	1,800
Less unamortized discount and issuance costs	22
Debt	1,778
CNA Financial [Member]
Debt Instrument [Line Items]
Debt, Gross	2,694
Less unamortized discount and issuance costs	13
Capital lease obligation	1	3
Debt	2,681
Diamond Offshore [Member]
Debt Instrument [Line Items]
Debt, Gross	2,000
Less unamortized discount and issuance costs	26
Debt	1,974
Boardwalk Pipeline [Member]
Debt Instrument [Line Items]
Debt, Gross	3,728
Less unamortized discount and issuance costs	26
Capital lease obligation	8	9
Debt	3,702
Loews Hotels And Co [Member]
Debt Instrument [Line Items]
Debt, Gross	653	648
Less unamortized discount and issuance costs	11
Debt	642
Consolidated Container [Member]
Debt Instrument [Line Items]
Debt, Gross	613
Less unamortized discount and issuance costs	14
Capital lease obligation	7	6
Debt	599
Consolidated Container [Member] \| Variable Rate Asset Based Lending Facility Due Two Thousand Twenty Two [Member]
Debt Instrument [Line Items]
Debt, Gross	9
2.6% Notes Due 2023 [Member] \| Loews Corporation [Member]
Debt Instrument [Line Items]
Debt, Gross	500	500
3.8% Notes Due 2026 [Member] \| Loews Corporation [Member]
Debt Instrument [Line Items]
Debt, Gross	500	500
6.0% Notes Due 2035 [Member] \| Loews Corporation [Member]
Debt Instrument [Line Items]
Debt, Gross	300	300
4.1% Notes Due 2043 [Member] \| Loews Corporation [Member]
Debt Instrument [Line Items]
Debt, Gross	500	500
7.0% Notes Due 2018 [Member] \| CNA Financial [Member]
Debt Instrument [Line Items]
Debt, Gross		150
5.9% Notes Due 2020 [Member] \| CNA Financial [Member]
Debt Instrument [Line Items]
Debt, Gross	500	500
5.8% Notes Due 2021 [Member] \| CNA Financial [Member]
Debt Instrument [Line Items]
Debt, Gross	400	400
7.3% Debentures Due 2023 [Member] \| CNA Financial [Member]
Debt Instrument [Line Items]
Debt, Gross	243	243
4.0% Notes Due 2024 [Member] \| CNA Financial [Member]
Debt Instrument [Line Items]
Debt, Gross	550	550
4.5% Notes Due 2026 [Member] \| CNA Financial [Member]
Debt Instrument [Line Items]
Debt, Gross	500	500
3.5% Notes Due 2027 [Member] \| CNA Financial [Member]
Debt Instrument [Line Items]
Debt, Gross	500	500
Variable Rate Note Due 2036 [Member] \| CNA Financial [Member]
Debt Instrument [Line Items]
Debt, Gross		30
Variable Rate Revolving Credit Facility Due 2022 [Member] \| Boardwalk Pipeline [Member]
Debt Instrument [Line Items]
Debt, Gross	580	385
5.8% Notes Due 2019 [Member] \| Boardwalk Pipeline [Member]
Debt Instrument [Line Items]
Debt, Gross	350	350
3.5% Senior Notes Due 2023 [Member] \| Diamond Offshore [Member]
Debt Instrument [Line Items]
Debt, Gross	250	250
7.9% Notes Due 2025 [Member] \| Diamond Offshore [Member]
Debt Instrument [Line Items]
Debt, Gross	500	500
5.7% Notes Due 2039 [Member] \| Diamond Offshore [Member]
Debt Instrument [Line Items]
Debt, Gross	500	500
4.9% Notes Due 2043 [Member] \| Diamond Offshore [Member]
Debt Instrument [Line Items]
Debt, Gross	750	750
3.4% Notes Due 2023 [Member] \| Boardwalk Pipeline [Member]
Debt Instrument [Line Items]
Debt, Gross	300	300
6.0% Notes Due 2026 [Member] \| Boardwalk Pipeline [Member]
Debt Instrument [Line Items]
Debt, Gross	550	550
5.2% Notes Due 2018 [Member] \| Boardwalk Pipeline [Member]
Debt Instrument [Line Items]
Debt, Gross		185
4.5% Notes Due 2021 [Member] \| Boardwalk Pipeline [Member]
Debt Instrument [Line Items]
Debt, Gross	440	440
4.0% Notes Due 2022 [Member] \| Boardwalk Pipeline [Member]
Debt Instrument [Line Items]
Debt, Gross	300	300
5.0% Notes Due 2024 [Member] \| Boardwalk Pipeline [Member]
Debt Instrument [Line Items]
Debt, Gross	600	600
4.5% Notes Due 2027 [Member] \| Boardwalk Pipeline [Member]
Debt Instrument [Line Items]
Debt, Gross	500	500
7.3% Debentures Due 2027 [Member] \| Boardwalk Pipeline [Member]
Debt Instrument [Line Items]
Debt, Gross	100	100
Senior Debt Variable Rate Term Loan Due 2024 [Member] \| Consolidated Container [Member] \| Variable Rate Term Loan Due Two Zero Two Four [Member]
Debt Instrument [Line Items]
Debt, Gross	$ 597	$ 604

Amount equal to the present value (the principal) at the beginning of the lease term of minimum lease payments during the lease term (excluding that portion of the payments representing executory costs such as insurance, maintenance, and taxes to be paid by the lessor, together with any profit thereon) net of payments or other amounts applied to the principal through the balance sheet date.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=84164817&loc=d3e45280-112737

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

+ Details

Name:	us-gaap_CapitalLeaseObligations
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=109500613&loc=SL6031897-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

Name:	us-gaap_DebtInstrumentCarryingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of unamortized debt discount (premium) and debt issuance costs.

+ References

+ Details

Name:	us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of long-term debt and capital lease obligations including current maturities.

+ References

No definition available.

+ Details

Name:	us-gaap_LongTermDebtAndCapitalLeaseObligationsIncludingCurrentMaturities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant