Segments - Consolidating Statement of Income by Segment (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Revenues:
Insurance premiums	$ 1,806	$ 1,767	$ 5,185	$ 5,196
Net investment income	557	561	1,639	1,570
Investment gains (losses)	16	45	93	18
Contract drilling revenues	357	340	1,113	1,141
Other revenues	785	574	2,150	1,842
Total	3,521	3,287	10,180	9,767
Expenses:
Insurance claims and policyholders' benefits	1,480	1,202	4,053	3,949
Amortization of deferred acquisition costs	309	314	926	926
Contract drilling expenses	198	187	598	598
Other operating expenses	1,047	898	2,978	3,416
Interest	223	130	504	403
Total	3,257	2,731	9,059	9,292
Income (loss) before income tax	264	556	1,121	475
Income tax (expense) benefit	(52)	(163)	(240)	(171)
Net income (loss)	212	393	881	304
Amounts attributable to noncontrolling interests	(55)	(66)	(198)	60
Net income (loss) attributable to Loews Corporation	157	327	683	364
CNA Financial [Member] | Operating Segments [Member]
Revenues:
Insurance premiums	1,806	1,767	5,185	5,196
Net investment income	509	524	1,529	1,461
Investment gains (losses)	16	45	93	30
Other revenues	110	97	329	297
Total	2,441	2,433	7,136	6,984
Expenses:
Insurance claims and policyholders' benefits	1,480	1,202	4,053	3,949
Amortization of deferred acquisition costs	309	314	926	926
Other operating expenses	379	402	1,086	1,158
Interest	83	39	166	127
Total	2,251	1,957	6,231	6,160
Income (loss) before income tax	190	476	905	824
Income tax (expense) benefit	(44)	(132)	(226)	(203)
Net income (loss)	146	344	679	621
Amounts attributable to noncontrolling interests	(16)	(36)	(71)	(64)
Net income (loss) attributable to Loews Corporation	130	308	608	557
Diamond Offshore [Member] | Operating Segments [Member]
Revenues:
Net investment income		1	1	1
Investment gains (losses)				(12)
Contract drilling revenues	357	340	1,113	1,141
Other revenues	11	9	30	69
Total	368	350	1,144	1,199
Expenses:
Contract drilling expenses	198	187	598	598
Other operating expenses	109	108	414	1,082
Interest	64	19	119	69
Total	371	314	1,131	1,749
Income (loss) before income tax	(3)	36	13	(550)
Income tax (expense) benefit	14	(22)	35	78
Net income (loss)	11	14	48	(472)
Amounts attributable to noncontrolling interests	(5)	(7)	(23)	228
Net income (loss) attributable to Loews Corporation	6	7	25	(244)
Boardwalk Pipeline [Member] | Operating Segments [Member]
Revenues:
Other revenues	301	306	987	961
Total	301	306	987	961
Expenses:
Other operating expenses	191	212	646	615
Interest	41	48	131	136
Total	232	260	777	751
Income (loss) before income tax	69	46	210	210
Income tax (expense) benefit	(18)	(9)	(46)	(44)
Net income (loss)	51	37	164	166
Amounts attributable to noncontrolling interests	(34)	(23)	(104)	(104)
Net income (loss) attributable to Loews Corporation	17	14	60	62
Loews Hotels And Co [Member] | Operating Segments [Member]
Revenues:
Other revenues	162	161	510	513
Total	162	161	510	513
Expenses:
Other operating expenses	147	151	443	479
Interest	7	6	20	17
Total	154	157	463	496
Income (loss) before income tax	8	4	47	17
Income tax (expense) benefit	(4)	(1)	(23)	(10)
Net income (loss)	4	3	24	7
Net income (loss) attributable to Loews Corporation	4	3	24	7
Corporate [Member]
Revenues:
Net investment income	48	36	109	108
Other revenues	201	1	294	2
Total	249	37	403	110
Expenses:
Other operating expenses	221	25	389	82
Interest	28	18	68	54
Total	$ 249	43	457	136
Income (loss) before income tax		(6)	(54)	(26)
Income tax (expense) benefit		1	20	8
Net income (loss)		(5)	(34)	(18)
Net income (loss) attributable to Loews Corporation		$ (5)	$ (34)	$ (18)