Debt - Schedule of Long-Term Debt Instruments (Parenthetical) (Detail) - USD ($)	1 Months Ended	12 Months Ended
	May 31, 2019	Dec. 31, 2019	Dec. 31, 2018
Loews Hotels And Co [Member]
Debt Instrument [Line Items]
Effective interest rate		4.70%	4.40%
5.9% Notes Due 2020 [Member] | CNA Financial [Member]
Debt Instrument [Line Items]
Stated interest rate	5.90%	5.90%
Maturity year		2020
Effective interest rate		6.00%
Debt authorized		$ 500,000,000
5.8% Notes Due 2021 [Member] | CNA Financial [Member]
Debt Instrument [Line Items]
Stated interest rate		5.80%
Maturity year		2021
Effective interest rate		5.90%
Debt authorized		$ 400,000,000
7.3% Debentures Due 2023 [Member] | CNA Financial [Member]
Debt Instrument [Line Items]
Stated interest rate		7.30%
Maturity year		2023
Effective interest rate		7.30%
Debt authorized		$ 250,000,000
4.0% Notes Due 2024 [Member] | CNA Financial [Member]
Debt Instrument [Line Items]
Stated interest rate		4.00%
Maturity year		2024
Effective interest rate		4.00%
Debt authorized		$ 550,000,000
4.5% Notes Due 2026 [Member] | CNA Financial [Member]
Debt Instrument [Line Items]
Stated interest rate		4.50%
Maturity year		2026
Effective interest rate		4.50%
Debt authorized		$ 500,000,000
3.5% Notes Due 2027 [Member] | CNA Financial [Member]
Debt Instrument [Line Items]
Stated interest rate		3.50%
Maturity year		2027
Effective interest rate		3.50%
Debt authorized		$ 500,000,000
3.9% Notes Due 2029 [Member] | CNA Financial [Member]
Debt Instrument [Line Items]
Stated interest rate		3.90%
Maturity year		2029
Effective interest rate		3.90%
Debt authorized		$ 500,000,000
3.5% notes due 2023 [Member] | Diamond Offshore [Member]
Debt Instrument [Line Items]
Stated interest rate		3.50%
Maturity year		2023
Effective interest rate		3.50%
Debt authorized		$ 250,000,000
7.9% Notes Due 2025 [Member] | Diamond Offshore [Member]
Debt Instrument [Line Items]
Stated interest rate		7.90%
Maturity year		2025
Effective interest rate		8.00%
Debt authorized		$ 500,000,000
5.7% Notes Due 2039 [Member] | Diamond Offshore [Member]
Debt Instrument [Line Items]
Stated interest rate		5.70%
Maturity year		2039
Effective interest rate		5.80%
Debt authorized		$ 500,000,000
4.9% Notes Due 2043 [Member] | Diamond Offshore [Member]
Debt Instrument [Line Items]
Stated interest rate		4.90%
Maturity year		2043
Effective interest rate		4.90%
Debt authorized		$ 750,000,000
Variable Rate Revolving Credit Facility Due 2022 [Member] | Boardwalk Pipelines [Member]
Debt Instrument [Line Items]
Maturity year		2022
Effective interest rate		3.00%	3.70%
5.8% Notes Due 2019 [Member] | Boardwalk Pipelines [Member]
Debt Instrument [Line Items]
Stated interest rate	5.80%	5.80%
Maturity year	2019	2019
Effective interest rate		5.90%
Debt authorized		$ 350,000,000
4.5% Notes Due 2021 [Member] | Boardwalk Pipelines [Member]
Debt Instrument [Line Items]
Stated interest rate		4.50%
Maturity year		2021
Effective interest rate		5.00%
Debt authorized		$ 440,000,000
4.0% Notes Due 2022 [Member] | Boardwalk Pipelines [Member]
Debt Instrument [Line Items]
Stated interest rate		4.00%
Maturity year		2022
Effective interest rate		4.40%
Debt authorized		$ 300,000,000
3.4% Notes Due 2023 [Member] | Boardwalk Pipelines [Member]
Debt Instrument [Line Items]
Stated interest rate		3.40%
Maturity year		2023
Effective interest rate		3.50%
Debt authorized		$ 300,000,000
5.0% Notes Due 2024 [Member] | Boardwalk Pipelines [Member]
Debt Instrument [Line Items]
Stated interest rate		5.00%
Maturity year		2024
Effective interest rate		5.20%
Debt authorized		$ 600,000,000
6.0% Notes Due 2026 [Member] | Boardwalk Pipelines [Member]
Debt Instrument [Line Items]
Stated interest rate		6.00%
Maturity year		2026
Effective interest rate		6.20%
Debt authorized		$ 550,000,000
4.5% Notes Due 2027 [Member] | Boardwalk Pipelines [Member]
Debt Instrument [Line Items]
Stated interest rate		4.50%
Maturity year		2027
Effective interest rate		4.60%
Debt authorized		$ 500,000,000
7.3% Debentures Due 2027 [Member] | Boardwalk Pipelines [Member]
Debt Instrument [Line Items]
Stated interest rate		7.30%
Maturity year		2027
Effective interest rate		8.10%
Debt authorized		$ 100,000,000
4.8% Notes Due 2029 [Member] | Boardwalk Pipelines [Member]
Debt Instrument [Line Items]
Stated interest rate	4.80%	4.80%
Maturity year		2029
Effective interest rate		4.90%
Debt authorized	$ 500,000,000	$ 500,000,000
Variable Rate Asset Based Lending Facility Due Two Thousand Twenty Two [Member] | Altium Packaging [Member]
Debt Instrument [Line Items]
Maturity year		2022
Effective interest rate		5.50%	5.50%
Variable Rate Term Loan Due Two Zero Two Four [Member] | Altium Packaging [Member]
Debt Instrument [Line Items]
Maturity year		2024
Effective interest rate		4.90%	5.00%
Variable Rate Term Loan Due Two zero Two Six [Member] | Altium Packaging [Member]
Debt Instrument [Line Items]
Maturity year		2026
Effective interest rate		5.30%	5.30%
Loews Corporation [Member] | 2.6% Notes Due 2023 [Member]
Debt Instrument [Line Items]
Stated interest rate		2.60%
Maturity year		2023
Effective interest rate		2.80%
Debt authorized		$ 500,000,000
Loews Corporation [Member] | 3.8% Notes Due 2026 [Member]
Debt Instrument [Line Items]
Stated interest rate		3.80%
Maturity year		2026
Effective interest rate		3.90%
Debt authorized		$ 500,000,000
Loews Corporation [Member] | 6.0% Notes Due 2035 [Member]
Debt Instrument [Line Items]
Stated interest rate		6.00%
Maturity year		2035
Effective interest rate		6.20%
Debt authorized		$ 300,000,000
Loews Corporation [Member] | 4.1% Notes Due 2043 [Member]
Debt Instrument [Line Items]
Stated interest rate		4.10%
Maturity year		2043
Effective interest rate		4.30%
Debt authorized		$ 500,000,000