Property, Plant and Equipment, Depreciation Expense and Capital Expenditures (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Depreciation		$ 673	$ 898	$ 880
Capital expenditures		670	1,058	995
Capitalized interest related to construction and upgrade of qualifying assets		14	18	27
Corporate [Member]
Property, Plant and Equipment [Abstract]
Depreciation		74	70	59
Capital expenditures		90	53	48
CNA Financial [Member]
Property, Plant and Equipment [Abstract]
Depreciation		56	64	76
Capital expenditures		25	26	99
Boardwalk Pipelines [Member]
Property, Plant and Equipment [Abstract]
Depreciation		361	348	346
Capital expenditures		415	418	487
Loews Hotels & Co [Member]
Property, Plant and Equipment [Abstract]
Depreciation		63	60	67
Capital expenditures		88	216	139
Diamond Offshore [Member]
Property, Plant and Equipment [Abstract]
Depreciation	[1]	119	356	332
Capital expenditures	[1]	$ 52	$ 345	$ 222

[1] Amounts presented for Diamond Offshore reflect the periods prior to deconsolidation. See Notes 2 and 20 for further discussion.