Segments (Details) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) Segment Subsidiaries	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Segments [Abstract]
Number of reportable segments | Segment				5
Number of individual operating subsidiaries | Subsidiaries				3
Assets [Abstract]
Assets		$ 79,464		$ 79,464		$ 82,243
Revenues [Abstract]
Insurance premiums		1,953	$ 1,890	5,672	$ 5,517
Net investment income (loss)		540	525	1,347	1,733
Investment gains (losses)	[1]	46	8	(1,312)	41
Non-insurance warranty revenue		317	292	926	858
Operating revenues and other		609	960	2,241	2,906
Total		3,465	3,675	8,874	11,055
Expenses [Abstract]
Insurance claims and policyholders' benefits		1,616	1,614	4,683	4,323
Amortization of deferred acquisition costs		360	345	1,046	1,025
Non-insurance warranty expense		293	278	859	801
Operating expenses and other		876	1,234	3,894	3,614
Interest		137	144	404	449
Total		3,282	3,615	10,886	10,212
Income (loss) before income tax		183	60	(2,012)	843
Income tax (expense) benefit		(21)	(21)	284	(183)
Net income (loss)		162	39	(1,728)	660
Amounts attributable to noncontrolling interests		(23)	33	400	55
Net income (loss) attributable to Loews Corporation		139	72	(1,328)	715
Operating Segments [Member]
Assets [Abstract]
Assets		79,464		79,464		82,243
Revenues [Abstract]
Insurance premiums		1,953	1,890	5,672	5,517
Net investment income (loss)		540	525	1,347	1,733
Investment gains (losses)		46	8	(1,312)	41
Non-insurance warranty revenue		317	292	926	858
Operating revenues and other		609	960	2,241	2,906
Total		3,465	3,675	8,874	11,055
Expenses [Abstract]
Insurance claims and policyholders' benefits		1,616	1,614	4,683	4,323
Amortization of deferred acquisition costs		360	345	1,046	1,025
Non-insurance warranty expense		293	278	859	801
Operating expenses and other		876	1,234	3,894	3,614
Interest		137	144	404	449
Total		3,282	3,615	10,886	10,212
Income (loss) before income tax		183	60	(2,012)	843
Income tax (expense) benefit		(21)	(21)	284	(183)
Net income (loss)		162	39	(1,728)	660
Amounts attributable to noncontrolling interests		(23)	33	400	55
Net income (loss) attributable to Loews Corporation		139	72	(1,328)	715
Operating Segments [Member] | CNA Financial [Member]
Assets [Abstract]
Assets		62,728		62,728		60,583
Revenues [Abstract]
Insurance premiums		1,953	1,890	5,672	5,517
Net investment income (loss)		517	487	1,380	1,573
Investment gains (losses)		46	8	(101)	41
Non-insurance warranty revenue		317	292	926	858
Operating revenues and other		7	9	20	22
Total		2,840	2,686	7,897	8,011
Expenses [Abstract]
Insurance claims and policyholders' benefits		1,616	1,614	4,683	4,323
Amortization of deferred acquisition costs		360	345	1,046	1,025
Non-insurance warranty expense		293	278	859	801
Operating expenses and other		268	291	851	854
Interest		52	31	114	120
Total		2,589	2,559	7,553	7,123
Income (loss) before income tax		251	127	344	888
Income tax (expense) benefit		(36)	(20)	(40)	(161)
Net income (loss)		215	107	304	727
Amounts attributable to noncontrolling interests		(23)	(11)	(32)	(77)
Net income (loss) attributable to Loews Corporation		192	96	272	650
Operating Segments [Member] | Boardwalk Pipelines [Member]
Assets [Abstract]
Assets		9,666		9,666		9,248
Revenues [Abstract]
Operating revenues and other		289	296	926	969
Total		289	296	926	969
Expenses [Abstract]
Operating expenses and other		219	212	633	616
Interest		44	45	127	136
Total		263	257	760	752
Income (loss) before income tax		26	39	166	217
Income tax (expense) benefit		(6)	(10)	(43)	(56)
Net income (loss)		20	29	123	161
Net income (loss) attributable to Loews Corporation		20	29	123	161
Operating Segments [Member] | Loews Hotels & Co [Member]
Assets [Abstract]
Assets		1,685		1,685		1,728
Revenues [Abstract]
Net investment income (loss)					1
Operating revenues and other		60	156	236	521
Total		60	156	236	522
Expenses [Abstract]
Operating expenses and other		114	145	404	464
Interest		8	6	24	16
Total		122	151	428	480
Income (loss) before income tax		(62)	5	(192)	42
Income tax (expense) benefit		15	(2)	48	(14)
Net income (loss)		(47)	3	(144)	28
Net income (loss) attributable to Loews Corporation		(47)	3	(144)	28
Operating Segments [Member] | Corporate [Member]
Assets [Abstract]
Assets		5,385		5,385		4,850
Revenues [Abstract]
Net investment income (loss)		23	36	(33)	153
Investment gains (losses)				(1,211)
Operating revenues and other		253	250	754	689
Total		276	286	(490)	842
Expenses [Abstract]
Operating expenses and other		275	264	810	740
Interest		33	31	96	85
Total		308	295	906	825
Income (loss) before income tax		(32)	(9)	(1,396)	17
Income tax (expense) benefit		6	1	293	(4)
Net income (loss)		(26)	(8)	(1,103)	13
Net income (loss) attributable to Loews Corporation		(26)	(8)	(1,103)	13
Operating Segments [Member] | Diamond Offshore [Member]
Assets [Abstract]
Assets	[2]	$ 0		0		$ 5,834
Revenues [Abstract]
Net investment income (loss)	[2]		2		6
Operating revenues and other	[2]		249	305	705
Total	[2]		251	305	711
Expenses [Abstract]
Operating expenses and other	[2]		322	1,196	940
Interest	[2]		31	43	92
Total	[2]		353	1,239	1,032
Income (loss) before income tax	[2]		(102)	(934)	(321)
Income tax (expense) benefit	[2]		10	26	52
Net income (loss)	[2]		(92)	(908)	(269)
Amounts attributable to noncontrolling interests	[2]		44	432	132
Net income (loss) attributable to Loews Corporation	[2]		$ (48)	$ (476)	$ (137)

[1] Gross investment gains on available-for-sale securities were $44 and $34 for the three months ended September 30, 2020 and 2019 and $175 and $98 for the nine months ended September 30, 2020 and 2019. Gross investment losses on available-for-sale securities were $18 and $31 for the three months ended September 30, 2020 and 2019 and $207 and $104 for the nine months ended September 30, 2020 and 2019. During the three and nine months ended September 30, 2020, $25 of investment gains and $44 of investment losses were recognized due to the change in fair value of non-redeemable preferred stock still held as of September 30, 2020. During the three and nine months ended September 30, 2019, $7 and $60 of investment gains were recognized due to the change in fair value of non-redeemable preferred stock still held as of September 30, 2019.

[2] Amounts presented for Diamond Offshore reflect the periods prior to the deconsolidation.