Consolidating Financial Information - Consolidating Balance Sheet Information (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
Condensed Financial Statements, Captions [Line Items]
Investments	$ 52,192	$ 52,032
Cash	271	364	301	295
Receivables	8,157	7,770
Property, plant and equipment	15,376	15,611
Goodwill	371	374
Other assets	1,640	1,616
Deferred acquisition costs of insurance subsidiaries	616	600
Total assets	78,623	78,367
Insurance reserves	36,705	36,380
Payable to brokers	926	673
Short term debt	687	335
Long term debt	9,863	10,333
Deferred income taxes	930	893
Other liabilities	4,882	5,103
Total liabilities	53,993	53,717
Total shareholders' equity	19,308	19,280
Noncontrolling interests	5,322	5,370
Total equity	24,630	24,650	25,117	24,906
Total liabilities and equity	78,623	78,367
Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Receivables	(32)	(56)
Deferred income taxes	(274)	(598)
Investments in capital stocks of subsidiaries	(15,702)	(15,974)
Other assets	11	14
Total assets	(15,997)	(16,614)
Deferred income taxes	(263)	(400)
Other liabilities	(32)	(240)
Total liabilities	(295)	(640)
Total shareholders' equity	(15,702)	(15,974)
Total equity	(15,702)	(15,974)
Total liabilities and equity	(15,997)	(16,614)
CNA Financial [Member] | Operating Segments [Member]
Condensed Financial Statements, Captions [Line Items]
Investments	45,932	46,262
Cash	201	190
Receivables	7,404	7,097
Property, plant and equipment	284	280
Deferred income taxes	86	222
Goodwill	114	117
Other assets	808	778
Deferred acquisition costs of insurance subsidiaries	616	600
Total assets	55,445	55,546
Insurance reserves	36,705	36,380
Payable to brokers	257	117
Short term debt	1
Long term debt	2,563	2,561
Deferred income taxes	9	11
Other liabilities	3,503	3,713
Total liabilities	43,038	42,782
Total shareholders' equity	11,125	11,457
Noncontrolling interests	1,282	1,307
Total equity	12,407	12,764
Total liabilities and equity	55,445	55,546
Diamond Offshore [Member] | Operating Segments [Member]
Condensed Financial Statements, Captions [Line Items]
Investments	191	234
Cash	7	16
Receivables	469	490
Property, plant and equipment	6,578	6,949
Goodwill	20	20
Other assets	266	307
Total assets	7,531	8,016
Payable to brokers	3	5
Short term debt	250	250
Long term debt	1,981	1,981
Deferred income taxes	397	514
Other liabilities	697	792
Total liabilities	3,328	3,542
Total shareholders' equity	2,245	2,359
Noncontrolling interests	1,958	2,115
Total equity	4,203	4,474
Total liabilities and equity	7,531	8,016
Boardwalk Pipeline [Member] | Operating Segments [Member]
Condensed Financial Statements, Captions [Line Items]
Cash	30	8
Receivables	158	128
Property, plant and equipment	7,626	7,649
Goodwill	237	237
Other assets	305	304
Total assets	8,356	8,326
Long term debt	3,568	3,690
Deferred income taxes	751	732
Other liabilities	385	400
Total liabilities	4,704	4,822
Total shareholders' equity	1,572	1,558
Noncontrolling interests	2,080	1,946
Total equity	3,652	3,504
Total liabilities and equity	8,356	8,326
Loews Hotels [Member] | Operating Segments [Member]
Condensed Financial Statements, Captions [Line Items]
Investments	48	75
Cash	6	9
Receivables	42	29
Property, plant and equipment	838	671
Deferred income taxes	2	2
Other assets	240	206
Total assets	1,176	992
Short term debt	36	85
Long term debt	471	421
Deferred income taxes	36	36
Other liabilities	22	17
Total liabilities	565	559
Total shareholders' equity	609	431
Noncontrolling interests	2	2
Total equity	611	433
Total liabilities and equity	1,176	992
Corporate and Other [Member]
Condensed Financial Statements, Captions [Line Items]
Investments	6,021	5,461
Cash	27	141
Receivables	116	82
Property, plant and equipment	50	62
Deferred income taxes	186	374
Investments in capital stocks of subsidiaries	15,702	15,974
Other assets	10	7
Total assets	22,112	22,101
Payable to brokers	666	551
Short term debt	400
Long term debt	1,280	1,680
Other liabilities	307	421
Total liabilities	2,653	2,652
Total shareholders' equity	19,459	19,449
Total equity	19,459	19,449
Total liabilities and equity	$ 22,112	$ 22,101