Debt - Schedule of Debt by Subsidiary (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Principal	$ 11,653	$ 10,871
Unamortized Discount and Issuance Costs	120	93
Net	11,533
Short Term Debt	280	110
Long Term Debt	11,253	10,668
Net	11,533
Loews Corporation [Member]
Debt Instrument [Line Items]
Principal	1,800
Unamortized Discount and Issuance Costs	24
Net	1,776
Long Term Debt	1,776
Net	1,776
CNA Financial [Member]
Debt Instrument [Line Items]
Principal	2,876
Unamortized Discount and Issuance Costs	15
Net	2,861
Short Term Debt	151
Long Term Debt	2,710
Net	2,861
Diamond Offshore [Member]
Debt Instrument [Line Items]
Principal	2,000
Unamortized Discount and Issuance Costs	28
Net	1,972
Long Term Debt	1,972
Net	1,972
Boardwalk Pipeline [Member]
Debt Instrument [Line Items]
Principal	3,719
Unamortized Discount and Issuance Costs	31
Net	3,688
Short Term Debt	1
Long Term Debt	3,687
Net	3,688
Loews Hotels And Co [Member]
Debt Instrument [Line Items]
Principal	648	$ 650
Unamortized Discount and Issuance Costs	5
Net	643
Short Term Debt	122
Long Term Debt	521
Net	643
Consolidated Container [Member]
Debt Instrument [Line Items]
Principal	610
Unamortized Discount and Issuance Costs	17
Net	593
Short Term Debt	6
Long Term Debt	587
Net	$ 593

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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-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://www.xbrl.org/2003/role/presentationRef
-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://www.xbrl.org/2003/role/presentationRef
-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

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28555-108399

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-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

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-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

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-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

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Amount of long-term debt and capital lease obligation due after one year or beyond the normal operating cycle, if longer.

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Amount of long-term debt and capital leases due within one year or the normal operating cycle, if longer.

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