Debt - Schedule of Long-Term Debt Instruments (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Debt, Gross	$ 11,643	$ 11,488
Less unamortized discount and issuance costs	110	112
Net	11,533	11,376
Loews Corporation [Member]
Debt Instrument [Line Items]
Debt, Gross	1,800
Less unamortized discount and issuance costs	21
Net	1,779
CNA Financial [Member]
Debt Instrument [Line Items]
Debt, Gross	2,693
Less unamortized discount and issuance costs	14
Finance lease obligation		1
Net	2,679
Diamond Offshore [Member]
Debt Instrument [Line Items]
Debt, Gross	2,000
Less unamortized discount and issuance costs	24
Net	1,976
Boardwalk Pipelines [Member]
Debt Instrument [Line Items]
Debt, Gross	3,592
Less unamortized discount and issuance costs	26
Finance lease obligation	7	8
Net	3,566
Loews Hotels [Member]
Debt Instrument [Line Items]
Debt, Gross	712	653
Less unamortized discount and issuance costs	7
Net	705
Altium Packaging Company [Member]
Debt Instrument [Line Items]
Debt, Gross	846
Less unamortized discount and issuance costs	18
Finance lease obligation	6	7
Net	828
Altium Packaging Company [Member] \| Variable Rate Term Loan Due Two Zero Two Four [Member]
Debt Instrument [Line Items]
Debt, Gross	591	597
Altium Packaging Company [Member] \| Variable Rate Term Loan Due Two zero Two Six [Member]
Debt Instrument [Line Items]
Debt, Gross	249
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
5.9% Notes Due 2020 [Member] \| CNA Financial [Member]
Debt Instrument [Line Items]
Debt, Gross		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
3.9% notes due 2029 [Member] \| CNA Financial [Member]
Debt Instrument [Line Items]
Debt, Gross	500
3.5% 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
Variable Rate Revolving Credit Facility Due 2022 [Member] \| Boardwalk Pipelines [Member]
Debt Instrument [Line Items]
Debt, Gross	295	580
Variable Rate Revolving Credit Facility Due 2022 [Member] \| Altium Packaging Company [Member]
Debt Instrument [Line Items]
Debt, Gross		9
5.8% Notes Due 2019 [Member] \| Boardwalk Pipelines [Member]
Debt Instrument [Line Items]
Debt, Gross		350
4.5% Notes Due 2021 [Member] \| Boardwalk Pipelines [Member]
Debt Instrument [Line Items]
Debt, Gross	440	440
4.0% Notes Due 2022 [Member] \| Boardwalk Pipelines [Member]
Debt Instrument [Line Items]
Debt, Gross	300	300
3.4% Notes Due 2023 [Member] \| Boardwalk Pipelines [Member]
Debt Instrument [Line Items]
Debt, Gross	300	300
5.0% Notes Due 2024 [Member] \| Boardwalk Pipelines [Member]
Debt Instrument [Line Items]
Debt, Gross	600	600
6.0% Notes Due 2026 [Member] \| Boardwalk Pipelines [Member]
Debt Instrument [Line Items]
Debt, Gross	550	550
4.5% Notes Due 2027 [Member] \| Boardwalk Pipelines [Member]
Debt Instrument [Line Items]
Debt, Gross	500	500
7.3% Debentures Due 2027 [Member] \| Boardwalk Pipelines [Member]
Debt Instrument [Line Items]
Debt, Gross	100	$ 100
4.8% notes due 2029 [Member] \| Boardwalk Pipelines [Member]
Debt Instrument [Line Items]
Debt, Gross	$ 500

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.

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- 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

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- 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

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- Definition

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

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- Definition

Amount of long-term debt and lease obligation, including portion classified as current.

+ References

No definition available.

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