Consolidating Financial Information - Consolidating Statement of Income Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Condensed Financial Statements, Captions [Line Items]
Insurance premiums	$ 7,212		$ 7,271		$ 6,881
Net investment income	2,163		2,425		2,177
Investment gains (losses)	54	[1]	16	[1]	48	[1]
Contract drilling revenues	2,737		2,844		2,936
Other revenues	2,159		2,057		2,030
Total	14,325		14,613		14,072
Expenses:
Insurance claims and policyholders' benefits	5,591		5,806		5,729
Amortization of deferred acquisition costs	1,317		1,362		1,274
Contract drilling expenses	1,524		1,573		1,537
Other operating expenses	3,585		3,170		3,084
Interest	498		425		426
Total	12,515		12,336		12,050
Income before income tax	1,810		2,277		2,022
Income tax (expense) benefit	(457)		(656)		(513)
Income (loss) from continuing operations	1,353		1,621		1,509
Discontinued operations, net	(391)		(552)		(399)
Net income (loss)	962		1,069		1,110
Amounts attributable to noncontrolling interests	(371)		(474)		(542)
Net income (loss) attributable to Loews Corporation	591		595		568
Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Intercompany interest and dividends	(782)		(736)		(683)
Other revenues					(7)
Total	(782)		(736)		(690)
Expenses:
Other operating expenses					(7)
Interest					(7)
Total					(14)
Income before income tax	(782)		(736)		(676)
Income (loss) from continuing operations	(782)		(736)		(676)
Net income (loss)	(782)		(736)		(676)
Net income (loss) attributable to Loews Corporation	(782)		(736)		(676)
CNA Financial [Member]
Expenses:
Interest	183		166		170
Income tax (expense) benefit	(322)		(363)		(242)
CNA Financial [Member] | Operating Segments [Member]
Condensed Financial Statements, Captions [Line Items]
Insurance premiums	7,212		7,271		6,881
Net investment income	2,067		2,282		2,110
Investment gains (losses)	54		16		51
Other revenues	359		363		322
Total	9,692		9,932		9,364
Expenses:
Insurance claims and policyholders' benefits	5,591		5,806		5,729
Amortization of deferred acquisition costs	1,317		1,362		1,274
Other operating expenses	1,386		1,315		1,324
Interest	183		166		170
Total	8,477		8,649		8,497
Income before income tax	1,215		1,283		867
Income tax (expense) benefit	(322)		(363)		(242)
Income (loss) from continuing operations	893		920		625
Discontinued operations, net	(197)		22		8
Net income (loss)	696		942		633
Amounts attributable to noncontrolling interests	(71)		(95)		(63)
Net income (loss) attributable to Loews Corporation	625		847		570
Diamond Offshore [Member]
Expenses:
Interest	62		25		46
Income tax (expense) benefit	(142)		(245)		(223)
Diamond Offshore [Member] | Operating Segments [Member]
Condensed Financial Statements, Captions [Line Items]
Net investment income	1		1		5
Contract drilling revenues	2,737		2,844		2,936
Other revenues	87		81		131
Total	2,825		2,926		3,072
Expenses:
Contract drilling expenses	1,524		1,573		1,537
Other operating expenses	725		554		572
Interest	62		25		46
Total	2,311		2,152		2,155
Income before income tax	514		774		917
Income tax (expense) benefit	(142)		(245)		(223)
Income (loss) from continuing operations	372		529		694
Net income (loss)	372		529		694
Amounts attributable to noncontrolling interests	(189)		(272)		(357)
Net income (loss) attributable to Loews Corporation	183		257		337
Boardwalk Pipeline [Member]
Expenses:
Interest	165		163		166
Income tax (expense) benefit	(11)		(56)		(70)
Boardwalk Pipeline [Member] | Operating Segments [Member]
Condensed Financial Statements, Captions [Line Items]
Net investment income	1		1
Investment gains (losses)					(3)
Other revenues	1,235		1,231		1,187
Total	1,236		1,232		1,184
Expenses:
Other operating expenses	931		828		717
Interest	165		163		166
Total	1,096		991		883
Income before income tax	140		241		301
Income tax (expense) benefit	(11)		(56)		(70)
Income (loss) from continuing operations	129		185		231
Net income (loss)	129		185		231
Amounts attributable to noncontrolling interests	(111)		(107)		(122)
Net income (loss) attributable to Loews Corporation	18		78		109
Loews Hotels [Member]
Expenses:
Interest	14		9		11
Income tax (expense) benefit	(10)		1		(7)
Loews Hotels [Member] | Operating Segments [Member]
Condensed Financial Statements, Captions [Line Items]
Net investment income					1
Other revenues	475		380		396
Total	475		380		397
Expenses:
Other operating expenses	440		375		372
Interest	14		9		11
Total	454		384		383
Income before income tax	21		(4)		14
Income tax (expense) benefit	(10)		1		(7)
Income (loss) from continuing operations	11		(3)		7
Net income (loss)	11		(3)		7
Net income (loss) attributable to Loews Corporation	11		(3)		7
Corporate and Other [Member]
Condensed Financial Statements, Captions [Line Items]
Net investment income	94		141		61
Intercompany interest and dividends	782		736		683
Other revenues	3		2		1
Total	879		879		745
Expenses:
Other operating expenses	103		98		106
Interest	74		62		40
Total	177		160		146
Income before income tax	702		719		599
Income tax (expense) benefit	28		7		29
Income (loss) from continuing operations	730		726		628
Discontinued operations, net	(194)		(574)		(407)
Net income (loss)	536		152		221
Net income (loss) attributable to Loews Corporation	$ 536		$ 152		$ 221

[1] Includes gross realized gains of $178, $198 and $241 and gross realized losses of $136, $179 and $187 on available-for-sale securities for the years ended December 31, 2014, 2013 and 2012.