Revenue from Contracts with Customers - Schedule of Disaggregation of Revenues (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	$ 1,213	$ 1,071	$ 2,474	$ 2,057
Other revenues	14	33	34	64
Operating revenues and other	1,227	1,104	2,508	2,121
CNA Financial [Member] \| Non-insurance Warranty [Member]
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	248	98	486	191
Diamond Offshore [Member] \| Drilling Contracts [Member]
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	268	398	564	773
Boardwalk Pipeline [Member] \| Transportation and Storage of Natural Gas and NGLs and Other Services [Member]
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	281	303	612	654
Loews Hotels And Co [Member] \| Lodging and Related Services [Member]
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	200	181	383	348
Corporate [Member] \| Rigid Plastic Packaging and Recycled Resin [Member]
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	$ 216	$ 91	$ 429	$ 91

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