Claim and Claim Adjustment Expense Reserves (Gross and net carried claim and claim adjustment expense reserves) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Gross Case Reserves	$ 12,262	$ 12,668
Gross IBNR Reserves	11,827	12,095
Total Gross Carried Claim and Claim Adjustment Expense Reserves	24,089	24,763	24,303	25,496
Net Case Reserves	10,176	10,356
Net IBNR Reserves	8,941	9,281
Total Net Carried Claim and Claim Adjustment Expense Reserves	19,117	19,637	19,283	19,374
CNA Specialty [Member]
Gross Case Reserves	2,270	2,292
Gross IBNR Reserves	4,419	4,456
Total Gross Carried Claim and Claim Adjustment Expense Reserves	6,689	6,748
Net Case Reserves	2,024	2,008
Net IBNR Reserves	4,142	4,104
Total Net Carried Claim and Claim Adjustment Expense Reserves	6,166	6,112
CNA Commercial [Member]
Gross Case Reserves	5,829	6,146
Gross IBNR Reserves	4,820	5,180
Total Gross Carried Claim and Claim Adjustment Expense Reserves	10,649	11,326
Net Case Reserves	5,358	5,611
Net IBNR Reserves	4,269	4,600
Total Net Carried Claim and Claim Adjustment Expense Reserves	9,627	10,211
Hardy [Member]
Gross Case Reserves	275	333
Gross IBNR Reserves	111	188
Total Gross Carried Claim and Claim Adjustment Expense Reserves	386	521
Net Case Reserves	159	192
Net IBNR Reserves	75	82
Total Net Carried Claim and Claim Adjustment Expense Reserves	234	274
Life and Group Non-Core [Member]
Gross Case Reserves	2,748	2,690
Gross IBNR Reserves	310	316
Total Gross Carried Claim and Claim Adjustment Expense Reserves	3,058	3,006
Net Case Reserves	2,352	2,253
Net IBNR Reserves	271	275
Total Net Carried Claim and Claim Adjustment Expense Reserves	2,623	2,528
Corporate and Other [Member]
Gross Case Reserves	1,140	1,207
Gross IBNR Reserves	2,167	1,955
Total Gross Carried Claim and Claim Adjustment Expense Reserves	3,307	3,162
Net Case Reserves	283	292
Net IBNR Reserves	184	220
Total Net Carried Claim and Claim Adjustment Expense Reserves	$ 467	$ 512