Consolidating Financial Information (Consolidating Balance Sheet Information) (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011	Dec. 31, 2010
Condensed Financial Statements, Captions [Line Items]
Investments	$ 52,914	$ 49,028
Cash	169	129	128	120
Receivables	9,474	9,259
Property, plant and equipment	13,564	13,618
Goodwill	939	908
Other assets	1,546	1,357
Deferred acquisition costs of insurance subsidiaries	603	552
Separate account business	345	417
Total assets	79,554	75,268
Insurance reserves	39,151	37,554
Payable to brokers	808	162
Short term debt	18	88
Long term debt	8,848	8,913
Deferred income taxes	1,122	622
Other liabilities	4,400	4,309
Separate account business	345	417
Total liabilities	54,692	52,065
Total shareholders' equity	19,839	18,772
Noncontrolling interests	5,023	4,431
Total equity	24,862	23,203	23,490	23,028
Total liabilities and equity	79,554	75,268
CNA Financial [Member]
Condensed Financial Statements, Captions [Line Items]
Investments	47,788	44,372
Cash	129	75
Receivables	8,458	8,302
Property, plant and equipment	285	272
Deferred income taxes	18	444
Goodwill	117	86
Other assets	810	544
Deferred acquisition costs of insurance subsidiaries	603	552
Separate account business	345	417
Total assets	58,553	55,064
Insurance reserves	39,151	37,554
Payable to brokers	700	72
Short term debt	13	83
Long term debt	2,557	2,525
Deferred income taxes	5
Other liabilities	3,163	2,971
Separate account business	345	417
Total liabilities	45,934	43,622
Total shareholders' equity	11,368	10,315
Noncontrolling interests	1,251	1,127
Total equity	12,619	11,442
Total liabilities and equity	58,553	55,064
Diamond Offshore [Member]
Condensed Financial Statements, Captions [Line Items]
Investments	1,468	1,206
Cash	24	30
Receivables	468	594
Property, plant and equipment	4,841	4,674
Goodwill	20	20
Other assets	371	453
Total assets	7,192	6,977
Payable to brokers		8
Long term debt	1,489	1,488
Deferred income taxes	529	530
Other liabilities	609	594
Total liabilities	2,627	2,620
Total shareholders' equity	2,313	2,209
Noncontrolling interests	2,252	2,148
Total equity	4,565	4,357
Total liabilities and equity	7,192	6,977
Boardwalk Pipeline [Member]
Condensed Financial Statements, Captions [Line Items]
Investments	2	10
Cash	9	13
Receivables	70	114
Property, plant and equipment	6,658	6,713
Goodwill	215	215
Other assets	311	307
Total assets	7,265	7,372
Payable to brokers	1	1
Long term debt	3,163	3,398
Deferred income taxes	583	493
Other liabilities	373	373
Total liabilities	4,120	4,265
Total shareholders' equity	1,625	1,951
Noncontrolling interests	1,520	1,156
Total equity	3,145	3,107
Total liabilities and equity	7,265	7,372
HighMount [Member]
Condensed Financial Statements, Captions [Line Items]
Investments	7	85
Receivables	78	109
Property, plant and equipment	1,226	1,576
Deferred income taxes	683	499
Goodwill	584	584
Other assets	19	19
Total assets	2,597	2,872
Payable to brokers	15	36
Long term debt	760	700
Other liabilities	116	104
Total liabilities	891	840
Total shareholders' equity	1,706	2,032
Total equity	1,706	2,032
Total liabilities and equity	2,597	2,872
Loews Hotels [Member]
Condensed Financial Statements, Captions [Line Items]
Investments	38	71
Cash	7	10
Receivables	31	33
Property, plant and equipment	505	338
Goodwill	3	3
Other assets	22	23
Total assets	606	478
Short term debt	5	5
Long term debt	285	208
Deferred income taxes	49	51
Other liabilities	19	20
Total liabilities	358	284
Total shareholders' equity	248	194
Total equity	248	194
Total liabilities and equity	606	478
Corporate And Other [Member]
Condensed Financial Statements, Captions [Line Items]
Investments	3,611	3,284
Cash		1
Receivables	564	226
Property, plant and equipment	49	45
Investments in capital stocks of subsidiaries	17,366	16,807
Other assets	13	11
Total assets	21,603	20,374
Payable to brokers	92	45
Long term debt	694	694
Deferred income taxes	657	491
Other liabilities	215	266
Total liabilities	1,658	1,496
Total shareholders' equity	19,945	18,878
Total equity	19,945	18,878
Total liabilities and equity	21,603	20,374
Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Receivables	(195)	(119)
Deferred income taxes	(701)	(943)
Investments in capital stocks of subsidiaries	(17,366)	(16,807)
Total assets	(18,262)	(17,869)
Long term debt	(100)	(100)
Deferred income taxes	(701)	(943)
Other liabilities	(95)	(19)
Total liabilities	(896)	(1,062)
Total shareholders' equity	(17,366)	(16,807)
Total equity	(17,366)	(16,807)
Total liabilities and equity	$ (18,262)	$ (17,869)