Business Segments - Consolidated Revenues and Income (Loss) by Business Segment (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Segment Reporting Information [Line Items]
Revenues	$ 3,593	$ 3,616	$ 7,281	$ 7,234
Income (loss) before income tax and noncontrolling interests	546	566	1,060	1,203
Income from continuing operations	303	261	568	583
Discontinued operations, net	(187)	8	(393)	(72)
Net income (loss)	116	269	175	511
Investment gains included in Revenues and Income (loss) before income tax and noncontrolling interests	(14)	(14)	28	5
Investment gains included in net income (loss)	(9)	(8)	15	4
CNA Financial [Member]
Segment Reporting Information [Line Items]
Revenues	2,440	2,450	4,903	4,905
Income (loss) before income tax and noncontrolling interests	365	272	666	622
Net income (loss)	235	172	435	390
CNA Financial [Member] | CNA Specialty [Member]
Segment Reporting Information [Line Items]
Revenues	993	954	1,972	1,910
Income (loss) before income tax and noncontrolling interests	269	220	481	435
Net income (loss)	160	129	288	257
Investment gains included in Revenues and Income (loss) before income tax and noncontrolling interests	(5)	(6)	7	(3)
Investment gains included in net income (loss)	(3)	(3)	4	(1)
CNA Financial [Member] | CNA Commercial [Member]
Segment Reporting Information [Line Items]
Revenues	1,027	1,104	2,068	2,205
Income (loss) before income tax and noncontrolling interests	80	161	207	359
Net income (loss)	48	94	125	209
Investment gains included in Revenues and Income (loss) before income tax and noncontrolling interests	(7)	(12)	5	(8)
Investment gains included in net income (loss)	(5)	(6)	2	(4)
CNA Financial [Member] | Life & Group Non-Core [Member]
Segment Reporting Information [Line Items]
Revenues	316	303	647	618
Income (loss) before income tax and noncontrolling interests	(23)	(84)	(39)	(107)
Net income (loss)	6	(36)	13	(36)
Investment gains included in Revenues and Income (loss) before income tax and noncontrolling interests	(4)		12	9
Investment gains included in net income (loss)	(3)		6	6
CNA Financial [Member] | Other [Member]
Segment Reporting Information [Line Items]
Revenues	104	89	216	172
Income (loss) before income tax and noncontrolling interests	39	(25)	17	(65)
Net income (loss)	21	(15)	9	(40)
Investment gains included in Revenues and Income (loss) before income tax and noncontrolling interests	2	4	4	7
Investment gains included in net income (loss)	2	1	3	3
Diamond Offshore [Member]
Segment Reporting Information [Line Items]
Revenues	701	760	1,411	1,492
Income (loss) before income tax and noncontrolling interests	112	257	280	462
Net income (loss)	42	87	111	169
Boardwalk Pipeline [Member]
Segment Reporting Information [Line Items]
Revenues	295	304	652	633
Income (loss) before income tax and noncontrolling interests	54	67	77	166
Net income (loss)	17	22	(1)	55
Loews Hotels [Member]
Segment Reporting Information [Line Items]
Revenues	112	101	217	195
Income (loss) before income tax and noncontrolling interests	9	2	14	2
Net income (loss)	5	1	8	1
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Revenues	45	1	98	9
Income (loss) before income tax and noncontrolling interests	6	(32)	23	(49)
Net income (loss)	$ 4	$ (21)	$ 15	$ (32)