Business Segments - Consolidated Revenues and Income (Loss) by Business Segment (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Segment Reporting Information [Line Items]
Revenues	$ 3,478us-gaap_Revenues	$ 3,688us-gaap_Revenues
Income (loss) before income tax and noncontrolling interests	105	514
Income from continuing operations	109	265
Discontinued operations, net		(206)
Net income (loss)	109us-gaap_NetIncomeLoss	59us-gaap_NetIncomeLoss
Investment gains included in Revenues and Income (loss) before income tax and noncontrolling interests	10	42
Investment gains included in net income (loss)	8	24
CNA Financial [Member]
Segment Reporting Information [Line Items]
Revenues	2,352	2,463
Income (loss) before income tax and noncontrolling interests	314	301
Net income (loss)	210	200
CNA Financial [Member] \| Other Non-Core [Member]
Segment Reporting Information [Line Items]
Revenues	334	343
Income (loss) before income tax and noncontrolling interests	(92)	(48)
Net income (loss)	(32)	(11)
Investment gains included in Revenues and Income (loss) before income tax and noncontrolling interests	1	18
Investment gains included in net income (loss)	2	10
CNA Financial [Member] \| Property and Casualty [Member] \| Specialty [Member]
Segment Reporting Information [Line Items]
Revenues	917	915
Income (loss) before income tax and noncontrolling interests	207	203
Net income (loss)	123	123
Investment gains included in Revenues and Income (loss) before income tax and noncontrolling interests	4	11
Investment gains included in net income (loss)	2	7
CNA Financial [Member] \| Property and Casualty [Member] \| Commercial [Member]
Segment Reporting Information [Line Items]
Revenues	895	946
Income (loss) before income tax and noncontrolling interests	186	119
Net income (loss)	110	73
Investment gains included in Revenues and Income (loss) before income tax and noncontrolling interests	4	10
Investment gains included in net income (loss)	3	7
CNA Financial [Member] \| Property and Casualty [Member] \| International [Member]
Segment Reporting Information [Line Items]
Revenues	206	259
Income (loss) before income tax and noncontrolling interests	13	27
Net income (loss)	9	15
Investment gains included in Revenues and Income (loss) before income tax and noncontrolling interests	1	3
Investment gains included in net income (loss)	1
Diamond Offshore [Member]
Segment Reporting Information [Line Items]
Revenues	627	710
Income (loss) before income tax and noncontrolling interests	(287)	168
Net income (loss)	(126)	69
Boardwalk Pipeline [Member]
Segment Reporting Information [Line Items]
Revenues	330	357
Income (loss) before income tax and noncontrolling interests	77	23
Net income (loss)	25	(18)
Loews Hotels [Member]
Segment Reporting Information [Line Items]
Revenues	139	105
Income (loss) before income tax and noncontrolling interests	10	5
Net income (loss)	5	3
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Revenues	30	53
Income (loss) before income tax and noncontrolling interests	(9)	17
Net income (loss)	$ (5)	$ 11

Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss Segments

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- Definition

Investment Gains Losses Included In Net Income

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Investment Gains Losses Included In Revenue And Income Loss Before Income Tax And Noncontrolling Interests

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- Definition

Amount of income (loss) from continuing operations attributable to the parent. Also defined as revenue less expenses and taxes from ongoing operations before extraordinary items but after deduction of those portions of income or loss from continuing operations that are allocable to noncontrolling interests.

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- Definition

Amount of income (loss) from a disposal group, net of income tax, reported as a separate component of income before extraordinary items after deduction or consideration of the amount allocable to noncontrolling interests. Includes, net of tax, income (loss) from operations during the phase-out period, gain (loss) on disposal, provision (or any reversals of earlier provisions) for loss on disposal, and adjustments of a prior period gain (loss) on disposal.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 810

-SubTopic 10

-Section 45

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

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-Section S99

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-Subparagraph (SX 210.7-04.19)

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

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-Article 5

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- Definition

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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