Debt - Schedule of Long-Term Debt Instruments (Parenthetical) (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Loews Hotels [Member]
Debt Instrument [Line Items]
Effective interest rate	4.10%
5.3% Notes Due 2016 [Member] | Loews Corporation [Member]
Debt Instrument [Line Items]
Stated interest rate	5.30%
Maturity year	2016
Effective interest rate	5.40%
Debt authorized	$ 400,000,000
2.6% Notes Due 2023 [Member] | Loews Corporation [Member]
Debt Instrument [Line Items]
Stated interest rate	2.60%
Maturity year	2023
Effective interest rate	2.80%
Debt authorized	$ 500,000,000
3.8% Notes Due 2026 [Member] | Loews Corporation [Member]
Debt Instrument [Line Items]
Stated interest rate	3.80%
Maturity year	2026
Effective interest rate	3.90%
Debt authorized	$ 500,000,000
6.0% Notes Due 2035 [Member] | Loews Corporation [Member]
Debt Instrument [Line Items]
Stated interest rate	6.00%
Maturity year	2035
Effective interest rate	6.20%
Debt authorized	$ 300,000,000
4.1% Notes Due 2043 [Member] | Loews Corporation [Member]
Debt Instrument [Line Items]
Stated interest rate	4.10%
Maturity year	2043
Effective interest rate	4.30%
Debt authorized	$ 500,000,000
6.5% Notes Due 2016 [Member] | CNA Financial [Member]
Debt Instrument [Line Items]
Stated interest rate	6.50%
Maturity year	2016
Effective interest rate	6.60%
Debt authorized	$ 350,000,000
7.0% Notes Due 2018 [Member] | CNA Financial [Member]
Debt Instrument [Line Items]
Stated interest rate	7.00%
Maturity year	2018
Effective interest rate	7.10%
Debt authorized	$ 150,000,000
7.4% Notes Due 2019 [Member] | CNA Financial [Member]
Debt Instrument [Line Items]
Stated interest rate	7.40%
Maturity year	2019
Effective interest rate	7.50%
Debt authorized	$ 350,000,000
5.9% Notes Due 2020 [Member] | CNA Financial [Member]
Debt Instrument [Line Items]
Stated interest rate	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
Variable Rate Note Due 2036 [Member] | CNA Financial [Member]
Debt Instrument [Line Items]
Maturity year	2036
Effective interest rate	4.30%	3.80%
Variable Rate Revolving Credit Facility Due 2020 [Member] | Diamond Offshore [Member]
Debt Instrument [Line Items]
Maturity year	2020
Effective interest rate	1.90%
5.9% Notes Due 2019 [Member] | Diamond Offshore [Member]
Debt Instrument [Line Items]
Stated interest rate	5.90%
Maturity year	2019
Effective interest rate	6.00%
Debt authorized	$ 500,000,000
3.5% Senior Notes Due 2023 [Member] | Diamond Offshore [Member]
Debt Instrument [Line Items]
Stated interest rate	3.50%
Maturity year	2023
Effective interest rate	3.60%
Debt authorized	$ 250,000,000
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	5.00%
Debt authorized	$ 750,000,000
Variable Rate Revolving Credit Facility Due 2021 [Member] | Boardwalk Pipeline [Member]
Debt Instrument [Line Items]
Maturity year	2021
Effective interest rate	2.00%	1.70%
5.9% Notes Due 2016 [Member] | Boardwalk Pipeline [Member]
Debt Instrument [Line Items]
Stated interest rate	5.90%
Maturity year	2016
Effective interest rate	6.00%
Debt authorized	$ 250,000,000
5.5% Notes Due 2017 [Member] | Boardwalk Pipeline [Member]
Debt Instrument [Line Items]
Stated interest rate	5.50%
Maturity year	2017
Effective interest rate	5.60%
Debt authorized	$ 300,000,000
6.3% Notes Due 2017 [Member] | Boardwalk Pipeline [Member]
Debt Instrument [Line Items]
Stated interest rate	6.30%
Maturity year	2017
Effective interest rate	6.40%
Debt authorized	$ 275,000,000
5.2% Notes Due 2018 [Member] | Boardwalk Pipeline [Member]
Debt Instrument [Line Items]
Stated interest rate	5.20%
Maturity year	2018
Effective interest rate	5.40%
Debt authorized	$ 185,000,000
5.8% Notes Due 2019 [Member] | Boardwalk Pipeline [Member]
Debt Instrument [Line Items]
Stated interest rate	5.80%
Maturity year	2019
Effective interest rate	5.90%
Debt authorized	$ 350,000,000
4.5% Notes Due 2021 [Member] | Boardwalk Pipeline [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 Pipeline [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 Pipeline [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 Pipeline [Member]
Debt Instrument [Line Items]
Stated interest rate	5.00%
Maturity year	2024
Effective interest rate	5.20%
Debt authorized	$ 600,000,000	$ 350,000,000
6.0% Notes Due 2026 [Member] | Boardwalk Pipeline [Member]
Debt Instrument [Line Items]
Stated interest rate	6.00%
Maturity year	2026
Effective interest rate	6.20%
Debt authorized	$ 550,000,000
7.3% Debentures Due 2027 [Member] | Boardwalk Pipeline [Member]
Debt Instrument [Line Items]
Stated interest rate	7.30%
Maturity year	2027
Effective interest rate	8.10%
Debt authorized	$ 100,000,000
Commercial Paper [Member]
Debt Instrument [Line Items]
Debt instrument, weighted average interest rate	0.90%
Commercial Paper [Member] | Diamond Offshore [Member]
Debt Instrument [Line Items]
Debt instrument, weighted average interest rate	0.90%