Property, Plant and Equipment - Depreciation Expense and Capital Expenditures (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Depreciation	$ 880	$ 854	$ 841
Capital Expend.	995	990	1,572
CNA Financial [Member]
Property, Plant and Equipment [Line Items]
Depreciation	76	80	67
Capital Expend.	99	101	128
Diamond Offshore [Member]
Property, Plant and Equipment [Line Items]
Depreciation	332	349	384
Capital Expend.	222	113	629
Boardwalk Pipeline [Member]
Property, Plant and Equipment [Line Items]
Depreciation	346	325	321
Capital Expend.	487	689	648
Loews Hotels And Co [Member]
Property, Plant and Equipment [Line Items]
Depreciation	67	63	63
Capital Expend.	139	57	164
Corporate [Member]
Property, Plant and Equipment [Line Items]
Depreciation	59	37	6
Capital Expend.	$ 48	$ 30	$ 3