Debt - Schedule of Long-Term Debt Instruments (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Debt, Gross	$ 10,871	$ 10,647
Less unamortized discount and issuance costs	93	87
Debt	10,778	10,560
Commercial Paper [Member]
Debt Instrument [Line Items]
Debt, Gross		287
Loews Corporation [Member]
Debt Instrument [Line Items]
Debt, Gross	1,800
Less unamortized discount and issuance costs	25
CNA Financial [Member]
Debt Instrument [Line Items]
Debt, Gross	2,728
Less unamortized discount and issuance costs	13
Capital lease obligation	5	4
Diamond Offshore [Member]
Debt Instrument [Line Items]
Debt, Gross	2,104
Less unamortized discount and issuance costs	19
Boardwalk Pipeline [Member]
Debt Instrument [Line Items]
Debt, Gross	3,589
Less unamortized discount and issuance costs	31
Capital lease obligation	9	10
Loews Hotels [Member]
Debt Instrument [Line Items]
Debt, Gross	650	598
Less unamortized discount and issuance costs	5
5.3% Notes Due 2016 [Member] | Loews Corporation [Member]
Debt Instrument [Line Items]
Debt, Gross		400
2.6% Notes Due 2023 [Member] | Loews Corporation [Member]
Debt Instrument [Line Items]
Debt, Gross	500	500
3.8% Notes Due 2026 [Member] | Loews Corporation [Member]
Debt Instrument [Line Items]
Debt, Gross	500
6.0% Notes Due 2035 [Member] | Loews Corporation [Member]
Debt Instrument [Line Items]
Debt, Gross	300	300
4.1% Notes Due 2043 [Member] | Loews Corporation [Member]
Debt Instrument [Line Items]
Debt, Gross	500	500
6.5% Notes Due 2016 [Member] | CNA Financial [Member]
Debt Instrument [Line Items]
Debt, Gross		350
7.0% Notes Due 2018 [Member] | CNA Financial [Member]
Debt Instrument [Line Items]
Debt, Gross	150	150
7.4% Notes Due 2019 [Member] | CNA Financial [Member]
Debt Instrument [Line Items]
Debt, Gross	350	350
5.9% Notes Due 2020 [Member] | CNA Financial [Member]
Debt Instrument [Line Items]
Debt, Gross	500	500
5.8% Notes Due 2021 [Member] | CNA Financial [Member]
Debt Instrument [Line Items]
Debt, Gross	400	400
7.3% Debentures Due 2023 [Member] | CNA Financial [Member]
Debt Instrument [Line Items]
Debt, Gross	243	243
4.0% Notes Due 2024 [Member] | CNA Financial [Member]
Debt Instrument [Line Items]
Debt, Gross	550	550
4.5% Notes Due 2026 [Member] | CNA Financial [Member]
Debt Instrument [Line Items]
Debt, Gross	500
Variable Rate Note Due 2036 [Member] | CNA Financial [Member]
Debt Instrument [Line Items]
Debt, Gross	30	30
Variable Rate Revolving Credit Facility Due 2020 [Member] | Diamond Offshore [Member]
Debt Instrument [Line Items]
Debt, Gross	104
5.9% Notes Due 2019 [Member] | Diamond Offshore [Member]
Debt Instrument [Line Items]
Debt, Gross	500	500
3.5% Senior Notes Due 2023 [Member] | Diamond Offshore [Member]
Debt Instrument [Line Items]
Debt, Gross	250	250
5.7% Notes Due 2039 [Member] | Diamond Offshore [Member]
Debt Instrument [Line Items]
Debt, Gross	500	500
4.9% Notes Due 2043 [Member] | Diamond Offshore [Member]
Debt Instrument [Line Items]
Debt, Gross	750	750
Variable Rate Revolving Credit Facility Due 2021 [Member] | Boardwalk Pipeline [Member]
Debt Instrument [Line Items]
Debt, Gross	180	375
5.9% Notes Due 2016 [Member] | Boardwalk Pipeline [Member]
Debt Instrument [Line Items]
Debt, Gross		250
5.5% Notes Due 2017 [Member] | Boardwalk Pipeline [Member]
Debt Instrument [Line Items]
Debt, Gross	300	300
6.3% Notes Due 2017 [Member] | Boardwalk Pipeline [Member]
Debt Instrument [Line Items]
Debt, Gross	275	275
5.2% Notes Due 2018 [Member] | Boardwalk Pipeline [Member]
Debt Instrument [Line Items]
Debt, Gross	185	185
5.8% Notes Due 2019 [Member] | Boardwalk Pipeline [Member]
Debt Instrument [Line Items]
Debt, Gross	350	350
4.5% Notes Due 2021 [Member] | Boardwalk Pipeline [Member]
Debt Instrument [Line Items]
Debt, Gross	440	440
4.0% Notes Due 2022 [Member] | Boardwalk Pipeline [Member]
Debt Instrument [Line Items]
Debt, Gross	300	300
3.4% Notes Due 2023 [Member] | Boardwalk Pipeline [Member]
Debt Instrument [Line Items]
Debt, Gross	300	300
5.0% Notes Due 2024 [Member] | Boardwalk Pipeline [Member]
Debt Instrument [Line Items]
Debt, Gross	600	600
6.0% Notes Due 2026 [Member] | Boardwalk Pipeline [Member]
Debt Instrument [Line Items]
Debt, Gross	550
7.3% Debentures Due 2027 [Member] | Boardwalk Pipeline [Member]
Debt Instrument [Line Items]
Debt, Gross	$ 100	$ 100