Debt - Schedule of Long-Term Debt Instruments (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Debt, Gross	$ 10,647	$ 10,736
Less unamortized discount	64	68
Debt	10,583	10,668
Commercial Paper [Member]
Debt Instrument [Line Items]
Debt, Gross	287
Loews Corporation [Member]
Debt Instrument [Line Items]
Debt, Gross	1,700
Less unamortized discount	19
CNA Financial [Member]
Debt Instrument [Line Items]
Debt, Gross	2,577
Less unamortized discount	11
Capital lease obligation	4	2
Diamond Offshore [Member]
Debt Instrument [Line Items]
Debt, Gross	2,287
Less unamortized discount	18
Boardwalk Pipeline [Member]
Debt Instrument [Line Items]
Debt, Gross	3,485
Less unamortized discount	16
Capital lease obligation	10	10
Loews Hotels [Member]
Debt Instrument [Line Items]
Debt, Gross	598	506
5.3% Notes Due 2016 [Member] | Loews Corporation [Member]
Debt Instrument [Line Items]
Debt, Gross	400	400
2.6% Notes Due 2023 [Member] | Loews Corporation [Member]
Debt Instrument [Line Items]
Debt, Gross	500	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	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
Variable Rate Note Due 2036 [Member] | CNA Financial [Member]
Debt Instrument [Line Items]
Debt, Gross	30	30
4.9% Notes Due 2015 [Member] | Diamond Offshore [Member]
Debt Instrument [Line Items]
Debt, Gross		250
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]
Debt Instrument [Line Items]
Debt, Gross	750	750
Variable Rate Revolving Credit Facility Due 2020 [Member] | Boardwalk Pipeline [Member]
Debt Instrument [Line Items]
Debt, Gross	375	120
Variable Rate Term Loan Due 2017 [Member] | Boardwalk Pipeline [Member]
Debt Instrument [Line Items]
Debt, Gross		200
4.6% Notes Due 2015 [Member] | Boardwalk Pipeline [Member]
Debt Instrument [Line Items]
Debt, Gross		250
5.1% Notes Due 2015 [Member] | Boardwalk Pipeline [Member]
Debt Instrument [Line Items]
Debt, Gross		275
5.9% Notes Due 2016 [Member] | Boardwalk Pipeline [Member]
Debt Instrument [Line Items]
Debt, Gross	250	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	350
7.3% Debentures Due 2027 [Member] | Boardwalk Pipeline [Member]
Debt Instrument [Line Items]
Debt, Gross	$ 100	$ 100