Consolidating Financial Information - Consolidating Balance Sheet Information (Detail) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015	Dec. 31, 2014
Assets:
Investments	$ 52,359	$ 49,400
Cash	348	440	$ 249	$ 364
Receivables	8,616	8,041
Property, plant and equipment	15,126	15,477
Goodwill	348	351
Other assets	1,766	1,699
Deferred acquisition costs of insurance subsidiaries	620	598
Total assets	79,183	76,006
Liabilities and Equity:
Insurance reserves	37,980	36,486
Payable to brokers	1,310	567
Short term debt	330	1,040
Long term debt	10,735	9,520
Deferred income taxes	604	382
Other liabilities	5,193	5,201
Total liabilities	56,152	53,196
Total shareholders' equity	17,945	17,561
Noncontrolling interests	5,086	5,249
Total equity	23,031	22,810	$ 24,332	$ 24,650
Total liabilities and equity	79,183	76,006
Eliminations [Member]
Assets:
Receivables	(21)	24
Deferred income taxes	(375)	(733)
Investments in capital stocks of subsidiaries	(15,232)	(15,129)
Other assets	15	17
Total assets	(15,613)	(15,821)
Liabilities and Equity:
Deferred income taxes	(360)	(712)
Other liabilities	(21)	20
Total liabilities	(381)	(692)
Total shareholders' equity	(15,232)	(15,129)
Total equity	(15,232)	(15,129)
Total liabilities and equity	(15,613)	(15,821)
CNA Financial [Member] | Operating Segments [Member]
Assets:
Investments	46,549	44,699
Cash	289	387
Receivables	7,799	7,384
Property, plant and equipment	269	333
Deferred income taxes	314	662
Goodwill	111	114
Other assets	930	848
Deferred acquisition costs of insurance subsidiaries	620	598
Total assets	56,881	55,025
Liabilities and Equity:
Insurance reserves	37,980	36,486
Payable to brokers	448	358
Short term debt	1	351
Long term debt	2,711	2,213
Deferred income taxes	2	5
Other liabilities	3,878	3,883
Total liabilities	45,020	43,296
Total shareholders' equity	10,638	10,516
Noncontrolling interests	1,223	1,213
Total equity	11,861	11,729
Total liabilities and equity	56,881	55,025
Diamond Offshore [Member] | Operating Segments [Member]
Assets:
Investments	90	117
Cash	14	13
Receivables	328	409
Property, plant and equipment	5,849	6,382
Other assets	225	233
Total assets	6,506	7,154
Liabilities and Equity:
Short term debt	327	287
Long term debt	1,980	1,980
Deferred income taxes	115	276
Other liabilities	467	496
Total liabilities	2,889	3,039
Total shareholders' equity	1,928	2,195
Noncontrolling interests	1,689	1,920
Total equity	3,617	4,115
Total liabilities and equity	6,506	7,154
Boardwalk Pipeline [Member] | Operating Segments [Member]
Assets:
Investments	150
Cash	13	4
Receivables	74	93
Property, plant and equipment	7,865	7,712
Goodwill	237	237
Other assets	317	319
Total assets	8,656	8,365
Liabilities and Equity:
Long term debt	3,626	3,458
Deferred income taxes	799	766
Other liabilities	509	510
Total liabilities	4,934	4,734
Total shareholders' equity	1,550	1,517
Noncontrolling interests	2,172	2,114
Total equity	3,722	3,631
Total liabilities and equity	8,656	8,365
Loews Hotels [Member] | Operating Segments [Member]
Assets:
Investments	93	81
Cash	13	12
Receivables	37	35
Property, plant and equipment	1,099	1,003
Deferred income taxes	3	3
Other assets	272	282
Total assets	1,517	1,416
Liabilities and Equity:
Short term debt	2	2
Long term debt	644	590
Deferred income taxes	48	47
Other liabilities	67	70
Total liabilities	761	709
Total shareholders' equity	754	705
Noncontrolling interests	2	2
Total equity	756	707
Total liabilities and equity	1,517	1,416
Corporate and Other [Member]
Assets:
Investments	5,477	4,503
Cash	19	24
Receivables	399	96
Property, plant and equipment	44	47
Deferred income taxes	58	68
Investments in capital stocks of subsidiaries	15,232	15,129
Other assets	7
Total assets	21,236	19,867
Liabilities and Equity:
Payable to brokers	862	209
Short term debt		400
Long term debt	1,774	1,279
Other liabilities	293	222
Total liabilities	2,929	2,110
Total shareholders' equity	18,307	17,757
Total equity	18,307	17,757
Total liabilities and equity	$ 21,236	$ 19,867