Debt, Long-term Debt (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020	Aug. 31, 2020	May 31, 2020	Dec. 31, 2019
Debt [Abstract]
Total long term debt and finance lease obligation		$ 10,197			$ 11,643
Less unamortized discount and issuance costs		88			110
Debt, net		10,109			11,533
3.2% Senior Notes Due 2030 [Member]
Debt [Abstract]
Interest rate				3.20%
Debt authorized				$ 500
Loews Corporation [Member]
Debt [Abstract]
Total long term debt and finance lease obligation		2,300
Less unamortized discount and issuance costs		24
Debt, net		2,276
Loews Corporation [Member] | 2.6% Senior Notes Due 2023 [Member]
Debt [Abstract]
Long term debt		$ 500			500
Interest rate		2.60%
Maturity date		2023
Effective interest rate		2.80%
Debt authorized		$ 500
Loews Corporation [Member] | 3.8% Senior Notes Due 2026 [Member]
Debt [Abstract]
Long term debt		$ 500			500
Interest rate		3.80%
Maturity date		2026
Effective interest rate		3.90%
Debt authorized		$ 500
Loews Corporation [Member] | 3.2% Senior Notes Due 2030 [Member]
Debt [Abstract]
Long term debt		$ 500
Interest rate		3.20%
Maturity date		2030
Effective interest rate		3.30%
Debt authorized		$ 500
Loews Corporation [Member] | 6.0% Senior Notes Due 2035 [Member]
Debt [Abstract]
Long term debt		$ 300			300
Interest rate		6.00%
Maturity date		2035
Effective interest rate		6.20%
Debt authorized		$ 300
Loews Corporation [Member] | 4.1% Senior Notes Due 2043 [Member]
Debt [Abstract]
Long term debt		$ 500			500
Interest rate		4.10%
Maturity date		2043
Effective interest rate		4.30%
Debt authorized		$ 500
CNA Financial [Member]
Debt [Abstract]
Total long term debt and finance lease obligation		2,793
Less unamortized discount and issuance costs		17
Debt, net		$ 2,776
CNA Financial [Member] | 5.8% Senior Notes Due 2021 [Member]
Debt [Abstract]
Long term debt					400
Interest rate		5.80%	5.80%
Maturity date		2021
Effective interest rate		5.90%
Debt authorized		$ 400	$ 400
CNA Financial [Member] | 7.3% Senior Debentures Due 2023 [Member]
Debt [Abstract]
Long term debt		$ 243			243
Interest rate		7.30%
Maturity date		2023
Effective interest rate		7.30%
Debt authorized		$ 250
CNA Financial [Member] | 4.0% Senior Notes Due 2024 [Member]
Debt [Abstract]
Long term debt		$ 550			550
Interest rate		4.00%
Maturity date		2024
Effective interest rate		4.00%
Debt authorized		$ 550
CNA Financial [Member] | 4.5% Senior Notes Due 2026 [Member]
Debt [Abstract]
Long term debt		$ 500			500
Interest rate		4.50%
Maturity date		2026
Effective interest rate		4.50%
Debt authorized		$ 500
CNA Financial [Member] | 3.5% Senior Notes Due 2027 [Member]
Debt [Abstract]
Long term debt		$ 500			500
Interest rate		3.50%
Maturity date		2027
Effective interest rate		3.50%
Debt authorized		$ 500
CNA Financial [Member] | 3.9% Senior Notes Due 2029 [Member]
Debt [Abstract]
Long term debt		$ 500			500
Interest rate		3.90%
Maturity date		2029
Effective interest rate		3.90%
Debt authorized		$ 500
CNA Financial [Member] | 2.1% Senior Notes Due 2030 [Member]
Debt [Abstract]
Long term debt		$ 500
Interest rate		2.10%	2.10%
Maturity date		2030
Effective interest rate		2.10%
Debt authorized		$ 500	$ 500
Boardwalk Pipelines [Member]
Debt [Abstract]
Finance lease obligation		7			7
Total long term debt and finance lease obligation		3,487
Less unamortized discount and issuance costs		25
Debt, net		3,462
Boardwalk Pipelines [Member] | Senior Variable Rate Revolving Credit Facility Due 2022 [Member]
Debt [Abstract]
Long term debt		$ 130			$ 295
Maturity date		2022
Effective interest rate		1.40%			3.00%
Boardwalk Pipelines [Member] | 4.5% Senior Notes Due 2021 [Member]
Debt [Abstract]
Long term debt					$ 440
Interest rate		4.50%	4.50%
Maturity date		2021
Effective interest rate		5.00%
Debt authorized		$ 440	$ 440
Boardwalk Pipelines [Member] | 4.0% Senior Notes Due 2022 [Member]
Debt [Abstract]
Long term debt		$ 300			300
Interest rate		4.00%
Maturity date		2022
Effective interest rate		4.40%
Debt authorized		$ 300
Boardwalk Pipelines [Member] | 3.4% Senior Notes Due 2023 [Member]
Debt [Abstract]
Long term debt		$ 300			300
Interest rate		3.40%
Maturity date		2023
Effective interest rate		3.50%
Debt authorized		$ 300
Boardwalk Pipelines [Member] | 5.0% Senior Notes Due 2024 [Member]
Debt [Abstract]
Long term debt		$ 600			600
Interest rate		5.00%
Maturity date		2024
Effective interest rate		5.20%
Debt authorized		$ 600
Boardwalk Pipelines [Member] | 6.0% Senior Notes Due 2026 [Member]
Debt [Abstract]
Long term debt		$ 550			550
Interest rate		6.00%
Maturity date		2026
Effective interest rate		6.20%
Debt authorized		$ 550
Boardwalk Pipelines [Member] | 4.5% Senior Notes Due 2027 [Member]
Debt [Abstract]
Long term debt		$ 500			500
Interest rate		4.50%
Maturity date		2027
Effective interest rate		4.60%
Debt authorized		$ 500
Boardwalk Pipelines [Member] | 7.3% Senior Debentures Due 2027 [Member]
Debt [Abstract]
Long term debt		$ 100			100
Interest rate		7.30%
Maturity date		2027
Effective interest rate		8.10%
Debt authorized		$ 100
Boardwalk Pipelines [Member] | 4.8% Senior Notes Due 2029 [Member]
Debt [Abstract]
Long term debt		$ 500			500
Interest rate		4.80%
Maturity date		2029
Effective interest rate		4.90%
Debt authorized		$ 500
Boardwalk Pipelines [Member] | 3.4% Senior Notes Due 2031 [Member]
Debt [Abstract]
Long term debt		$ 500
Interest rate		3.40%	3.40%
Maturity date		2031
Effective interest rate		3.50%
Debt authorized		$ 500	$ 500
Loews Hotels & Co [Member]
Debt [Abstract]
Total long term debt and finance lease obligation		750
Less unamortized discount and issuance costs		8
Debt, net		742
Loews Hotels & Co [Member] | Senior Debt, Principally Mortgages [Member]
Debt [Abstract]
Long term debt		$ 750			712
Effective interest rate		4.70%
Altium Packaging [Member]
Debt [Abstract]
Finance lease obligation		$ 26			6
Total long term debt and finance lease obligation		867
Less unamortized discount and issuance costs		14
Debt, net		853
Altium Packaging [Member] | Senior Variable Rate Asset Based Lending Facility Due 2022 [Member]
Debt [Abstract]
Long term debt		$ 10
Maturity date		2022
Effective interest rate		3.50%
Altium Packaging [Member] | Senior Variable Rate Term Loan Due 2024 [Member]
Debt [Abstract]
Long term debt		$ 585			$ 591
Maturity date		2024
Effective interest rate		4.70%			4.90%
Altium Packaging [Member] | Senior Variable Rate Term Loan Due 2026 [Member]
Debt [Abstract]
Long term debt		$ 246			$ 249
Maturity date		2026
Effective interest rate		4.10%			5.30%
Diamond Offshore [Member] | 3.5% Senior Notes Due 2023 [Member]
Debt [Abstract]
Long term debt	[1]				$ 250
Interest rate	[1]	3.50%
Maturity date	[1]	2023
Effective interest rate	[1]	3.50%
Debt authorized	[1]	$ 250
Diamond Offshore [Member] | 7.9% Senior Notes Due 2025 [Member]
Debt [Abstract]
Long term debt	[1]				500
Interest rate	[1]	7.90%
Maturity date	[1]	2025
Effective interest rate	[1]	8.00%
Debt authorized	[1]	$ 500
Diamond Offshore [Member] | 5.7% Senior Notes Due 2039 [Member]
Debt [Abstract]
Long term debt	[1]				500
Interest rate	[1]	5.70%
Maturity date	[1]	2039
Effective interest rate	[1]	5.80%
Debt authorized	[1]	$ 500
Diamond Offshore [Member] | 4.9% Senior Notes Due 2043 [Member]
Debt [Abstract]
Long term debt	[1]				$ 750
Interest rate	[1]	4.90%
Maturity date	[1]	2043
Effective interest rate	[1]	4.90%
Debt authorized	[1]	$ 750

[1] Amounts presented for Diamond Offshore reflects the period prior to the deconsolidation.