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Revenue from Contracts with Customers (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	$ 959	$ 967
Other revenues	23	18
Operating revenues and other	982	985
Contract with Customer, Asset and Liability [Abstract]
Receivables from contracts with customers, included within receivables	486		$ 458
Deferred revenue	3,848		3,779
Revenue recognized	297	285
Revenue, Performance Obligation Satisfied over Time [Abstract]
Performance obligations	12,900
Deferred Non-insurance Warranty Revenue and Other Liabilities [Member]
Contract with Customer, Asset and Liability [Abstract]
Deferred revenue	4,000		$ 3,900
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-10
Revenue, Performance Obligation Satisfied over Time [Abstract]
Performance obligations	$ 1,400
Expected timing of satisfaction, period	9 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Performance Obligation Satisfied over Time [Abstract]
Performance obligations	$ 2,100
Expected timing of satisfaction, period	1 year
Non-insurance Warranty Services [Member] \| CNA Financial [Member]
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	$ 301	281
Contract Drilling [Member] \| Diamond Offshore [Member]
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	229	234
Transportation and Storage of Natural Gas and NGLs and Other Services [Member] \| Boardwalk Pipeline [Member]
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	332	339
Lodging and Related Services [Member] \| Loews Hotels & Co [Member]
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	142	180
Rigid Plastic Packaging and Recycled Resin [Member] \| Corporate [Member]
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	$ 256	$ 214