Segments - Consolidating Statement of Income and Total Assets by Segment (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues:
Insurance premiums									$ 7,312	$ 6,988	$ 6,924
Net investment income									1,817	2,182	2,135
Investment gains									(57)	122	50
Non-insurance warranty revenue (Notes 1 and 13)									1,007	390	361
Operating revenues and other									3,987	4,053	3,635
Total	$ 3,287	$ 3,608	$ 3,590	$ 3,581	$ 3,555	$ 3,521	$ 3,359	$ 3,300	14,066	13,735	13,105
Expenses:
Insurance claims and policyholders' benefits									5,572	5,310	5,283
Amortization of deferred acquisition costs									1,335	1,233	1,235
Non-insurance warranty expense (Notes 1 and 13)									923	299	271
Operating expenses and other									4,828	4,665	4,844
Interest									574	646	536
Total									13,232	12,153	12,169
Income (loss) before income tax									834	1,582	936
Income tax (expense) benefit									(128)	(170)	(220)
Net income (loss)									706	1,412	716
Amounts attributable to noncontrolling interests									(70)	(248)	(62)
Net income (loss) attributable to Loews Corporation	(165)	$ 278	$ 230	$ 293	481	$ 157	$ 231	$ 295	636	1,164	654
Total assets	78,316				79,586				78,316	79,586
CNA Financial [Member] | Operating Segments [Member]
Revenues:
Insurance premiums									7,312	6,988	6,924
Net investment income									1,817	2,034	1,988
Investment gains									(57)	122	62
Non-insurance warranty revenue (Notes 1 and 13)									1,007	390	361
Operating revenues and other									55	49	49
Total									10,134	9,583	9,384
Expenses:
Insurance claims and policyholders' benefits									5,572	5,310	5,283
Amortization of deferred acquisition costs									1,335	1,233	1,235
Non-insurance warranty expense (Notes 1 and 13)									923	299	271
Operating expenses and other									1,203	1,224	1,287
Interest									138	203	167
Total									9,171	8,269	8,243
Income (loss) before income tax									963	1,314	1,141
Income tax (expense) benefit									(151)	(419)	(279)
Net income (loss)									812	895	862
Amounts attributable to noncontrolling interests									(86)	(94)	(88)
Net income (loss) attributable to Loews Corporation									726	801	774
Total assets	57,123				56,539				57,123	56,539
Diamond Offshore [Member] | Operating Segments [Member]
Revenues:
Net investment income									8	2	1
Investment gains											(12)
Operating revenues and other									1,085	1,498	1,600
Total									1,093	1,500	1,589
Expenses:
Operating expenses and other									1,196	1,373	1,970
Interest									123	149	90
Total									1,319	1,522	2,060
Income (loss) before income tax									(226)	(22)	(471)
Income tax (expense) benefit									30	4	111
Net income (loss)									(196)	(18)	(360)
Amounts attributable to noncontrolling interests									84	(9)	174
Net income (loss) attributable to Loews Corporation									(112)	(27)	(186)
Total assets	6,036				6,251				6,036	6,251
Boardwalk Pipeline [Member] | Operating Segments [Member]
Revenues:
Operating revenues and other									1,227	1,325	1,316
Total									1,227	1,325	1,316
Expenses:
Operating expenses and other									820	861	835
Interest									176	171	183
Total									996	1,032	1,018
Income (loss) before income tax									231	293	298
Income tax (expense) benefit									(28)	232	(61)
Net income (loss)									203	525	237
Amounts attributable to noncontrolling interests									(68)	(145)	(148)
Net income (loss) attributable to Loews Corporation									135	380	89
Total assets	9,131				8,972				9,131	8,972
Loews Hotels And Co [Member] | Operating Segments [Member]
Revenues:
Net investment income									2
Operating revenues and other									753	682	667
Total									755	682	667
Expenses:
Operating expenses and other									653	589	621
Interest									29	28	24
Total									682	617	645
Income (loss) before income tax									73	65	22
Income tax (expense) benefit									(25)	(1)	(10)
Net income (loss)									48	64	12
Net income (loss) attributable to Loews Corporation									48	64	12
Total assets	1,812				1,558				1,812	1,558
Corporate [Member]
Revenues:
Net investment income									(10)	146	146
Operating revenues and other									867	499	3
Total									857	645	149
Expenses:
Operating expenses and other									956	618	131
Interest									108	95	72
Total									1,064	713	203
Income (loss) before income tax									(207)	(68)	(54)
Income tax (expense) benefit									46	14	19
Net income (loss)									(161)	(54)	(35)
Net income (loss) attributable to Loews Corporation									(161)	(54)	$ (35)
Total assets	$ 4,214				$ 6,266				$ 4,214	$ 6,266