Segments - Consolidating Statement of Income and Total Assets by Segment (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenues:
Insurance premiums									$ 6,924	$ 6,921	$ 7,212
Net investment income									2,135	1,866	2,163
Investment gains (losses)									50	(71)	54
Contract drilling revenues									1,525	2,360	2,737
Other revenues									2,471	2,339	2,159
Total	$ 3,338	$ 3,287	$ 3,307	$ 3,173	$ 3,333	$ 3,169	$ 3,435	$ 3,478	13,105	13,415	14,325
Expenses:
Insurance claims and policyholders' benefits									5,283	5,384	5,591
Amortization of deferred acquisition costs									1,235	1,540	1,317
Contract drilling expenses									772	1,228	1,524
Other operating expenses									4,343	4,499	3,585
Interest									536	520	498
Total									12,169	13,171	12,515
Income (loss) before income tax									936	244	1,810
Income tax (expense) benefit									(220)	43	(457)
Income from continuing operations									716	287	1,353
Discontinued operations, net											(391)
Net income									716	287	962
Amounts attributable to noncontrolling interests									(62)	(27)	(371)
Net income (loss) attributable to Loews Corporation	290	$ 327	$ (65)	$ 102	(201)	$ 182	$ 170	$ 109	654	260	591
Total assets	76,594				76,006				76,594	76,006
CNA Financial [Member] | Operating Segments [Member]
Revenues:
Insurance premiums									6,924	6,921	7,212
Net investment income									1,988	1,840	2,067
Investment gains (losses)									62	(71)	54
Other revenues									410	411	359
Total									9,384	9,101	9,692
Expenses:
Insurance claims and policyholders' benefits									5,283	5,384	5,591
Amortization of deferred acquisition costs									1,235	1,540	1,317
Other operating expenses									1,558	1,469	1,386
Interest									167	155	183
Total									8,243	8,548	8,477
Income (loss) before income tax									1,141	553	1,215
Income tax (expense) benefit									(279)	(71)	(322)
Income from continuing operations											893
Discontinued operations, net											(197)
Net income									862	482	696
Amounts attributable to noncontrolling interests									(88)	(49)	(71)
Net income (loss) attributable to Loews Corporation									774	433	625
Total assets	55,207				55,025				55,207	55,025
Diamond Offshore [Member] | Operating Segments [Member]
Revenues:
Net investment income									1	3	1
Investment gains (losses)									(12)
Contract drilling revenues									1,525	2,360	2,737
Other revenues									75	65	87
Total									1,589	2,428	2,825
Expenses:
Contract drilling expenses									772	1,228	1,524
Other operating expenses									1,198	1,508	725
Interest									90	94	62
Total									2,060	2,830	2,311
Income (loss) before income tax									(471)	(402)	514
Income tax (expense) benefit									111	117	(142)
Income from continuing operations											372
Net income									(360)	(285)	372
Amounts attributable to noncontrolling interests									174	129	(189)
Net income (loss) attributable to Loews Corporation									(186)	(156)	183
Total assets	6,371				7,154				6,371	7,154
Boardwalk Pipeline [Member] | Operating Segments [Member]
Revenues:
Net investment income										1	1
Other revenues									1,316	1,253	1,235
Total									1,316	1,254	1,236
Expenses:
Other operating expenses									835	851	931
Interest									183	176	165
Total									1,018	1,027	1,096
Income (loss) before income tax									298	227	140
Income tax (expense) benefit									(61)	(46)	(11)
Income from continuing operations											129
Net income									237	181	129
Amounts attributable to noncontrolling interests									(148)	(107)	(111)
Net income (loss) attributable to Loews Corporation									89	74	18
Total assets	8,706				8,365				8,706	8,365
Loews Hotels [Member] | Operating Segments [Member]
Revenues:
Other revenues									667	604	475
Total									667	604	475
Expenses:
Other operating expenses									621	555	440
Interest									24	21	14
Total									645	576	454
Income (loss) before income tax									22	28	21
Income tax (expense) benefit									(10)	(16)	(10)
Income from continuing operations											11
Net income									12	12	11
Net income (loss) attributable to Loews Corporation									12	12	11
Total assets	1,498				1,416				1,498	1,416
Corporate [Member]
Revenues:
Net investment income									146	22	94
Other revenues									3	6	3
Total									149	28	97
Expenses:
Other operating expenses									131	116	103
Interest									72	74	74
Total									203	190	177
Income (loss) before income tax									(54)	(162)	(80)
Income tax (expense) benefit									19	59	28
Income from continuing operations											(52)
Discontinued operations, net											(194)
Net income									(35)	(103)	(246)
Net income (loss) attributable to Loews Corporation									(35)	(103)	$ (246)
Total assets	$ 4,812				$ 4,046				$ 4,812	$ 4,046