Consolidating Financial Information - Consolidating Balance Sheet Information (Detail) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014	Dec. 31, 2013
Condensed Financial Statements, Captions [Line Items]
Investments	$ 51,048	$ 52,032
Cash	249	364	$ 277	$ 294
Receivables	8,097	7,770
Property, plant and equipment	15,917	15,611
Goodwill	373	374
Other assets	1,710	1,616
Deferred acquisition costs of insurance subsidiaries	621	600
Total assets	78,015	78,367
Insurance reserves	36,368	36,380
Payable to brokers	741	673
Short term debt	1,061	335
Long term debt	9,791	10,333
Deferred income taxes	773	893
Other liabilities	4,949	5,103
Total liabilities	53,683	53,717
Total shareholders' equity	18,982	19,280
Noncontrolling interests	5,350	5,370
Total equity	24,332	24,650	$ 25,355	$ 24,906
Total liabilities and equity	78,015	78,367
Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Receivables	(94)	(56)
Deferred income taxes	(431)	(598)
Investments in capital stocks of subsidiaries	(15,756)	(15,974)
Other assets	12	14
Total assets	(16,269)	(16,614)
Deferred income taxes	(419)	(400)
Other liabilities	(94)	(240)
Total liabilities	(513)	(640)
Total shareholders' equity	(15,756)	(15,974)
Total equity	(15,756)	(15,974)
Total liabilities and equity	(16,269)	(16,614)
CNA Financial [Member] | Operating Segments [Member]
Condensed Financial Statements, Captions [Line Items]
Investments	45,332	46,262
Cash	145	190
Receivables	7,365	7,097
Property, plant and equipment	304	280
Deferred income taxes	283	222
Goodwill	116	117
Other assets	835	778
Deferred acquisition costs of insurance subsidiaries	621	600
Total assets	55,001	55,546
Insurance reserves	36,368	36,380
Payable to brokers	196	117
Short term debt	1
Long term debt	2,564	2,561
Deferred income taxes	8	11
Other liabilities	3,660	3,713
Total liabilities	42,797	42,782
Total shareholders' equity	10,944	11,457
Noncontrolling interests	1,260	1,307
Total equity	12,204	12,764
Total liabilities and equity	55,001	55,546
Diamond Offshore [Member] | Operating Segments [Member]
Condensed Financial Statements, Captions [Line Items]
Investments	102	234
Cash	10	16
Receivables	537	490
Property, plant and equipment	6,934	6,949
Goodwill	20	20
Other assets	268	307
Total assets	7,871	8,016
Payable to brokers		5
Short term debt	625	250
Long term debt	1,982	1,981
Deferred income taxes	393	514
Other liabilities	591	792
Total liabilities	3,591	3,542
Total shareholders' equity	2,285	2,359
Noncontrolling interests	1,995	2,115
Total equity	4,280	4,474
Total liabilities and equity	7,871	8,016
Boardwalk Pipeline [Member] | Operating Segments [Member]
Condensed Financial Statements, Captions [Line Items]
Cash	20	8
Receivables	123	128
Property, plant and equipment	7,633	7,649
Goodwill	237	237
Other assets	324	304
Total assets	8,337	8,326
Long term debt	3,493	3,690
Deferred income taxes	755	732
Other liabilities	425	400
Total liabilities	4,673	4,822
Total shareholders' equity	1,571	1,558
Noncontrolling interests	2,093	1,946
Total equity	3,664	3,504
Total liabilities and equity	8,337	8,326
Loews Hotels [Member] | Operating Segments [Member]
Condensed Financial Statements, Captions [Line Items]
Investments	100	75
Cash	11	9
Receivables	45	29
Property, plant and equipment	997	671
Deferred income taxes	2	2
Other assets	261	206
Total assets	1,416	992
Short term debt	35	85
Long term debt	471	421
Deferred income taxes	36	36
Other liabilities	66	17
Total liabilities	608	559
Total shareholders' equity	806	431
Noncontrolling interests	2	2
Total equity	808	433
Total liabilities and equity	1,416	992
Corporate and Other [Member]
Condensed Financial Statements, Captions [Line Items]
Investments	5,514	5,461
Cash	63	141
Receivables	121	82
Property, plant and equipment	49	62
Deferred income taxes	146	374
Investments in capital stocks of subsidiaries	15,756	15,974
Other assets	10	7
Total assets	21,659	22,101
Payable to brokers	545	551
Short term debt	400
Long term debt	1,281	1,680
Other liabilities	301	421
Total liabilities	2,527	2,652
Total shareholders' equity	19,132	19,449
Total equity	19,132	19,449
Total liabilities and equity	$ 21,659	$ 22,101