Property, Plant and Equipment - Depreciation Expense and Capital Expenditures (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Depreciation	$ 898	$ 880	$ 854
Capital Expend.	1,058	995	990
Corporate [Member]
Property, Plant and Equipment [Line Items]
Depreciation	70	59	37
Capital Expend.	53	48	30
CNA Financial [Member]
Property, Plant and Equipment [Line Items]
Depreciation	64	76	80
Capital Expend.	26	99	101
Diamond Offshore [Member]
Property, Plant and Equipment [Line Items]
Depreciation	356	332	349
Capital Expend.	345	222	113
Boardwalk Pipelines [Member]
Property, Plant and Equipment [Line Items]
Depreciation	348	346	325
Capital Expend.	418	487	689
Loews Hotels And Co [Member]
Property, Plant and Equipment [Line Items]
Depreciation	60	67	63
Capital Expend.	$ 216	$ 139	$ 57