Claim and Claim Adjustment Expense Reserves - Reconciliation of Claim and Claim Adjustment Expense Reserves (Detail) - CNA Financial [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Liability for Claims and Claims Adjustment Expense [Line Items]
Gross reserves, beginning of year	$ 22,663	$ 23,271	$ 24,089
Ceded reserves, beginning of year	4,087	4,344	4,972
Net reserves, beginning of year	18,576	18,927	19,117
Change in net reserves due to disposition of subsidiaries			(13)
Net incurred claim and claim adjustment expenses:
Provision for insured events of current year	5,025	4,934	5,043
Decrease in provision for insured events of prior years	(342)	(255)	(36)
Amortization of discount	175	166	161
Total net incurred	4,858	4,845	5,168
Net payments attributable to:
Current year events	(967)	(856)	(945)
Prior year events	(4,167)	(4,089)	(4,355)
Total net payments	(5,134)	(4,945)	(5,300)
Foreign currency translation adjustment and other	(51)	(251)	(45)
Net reserves, end of year	18,249	18,576	18,927
Ceded reserves, end of year	4,094	4,087	4,344
Gross reserves, end of year	$ 22,343	$ 22,663	$ 23,271