Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=68055307&loc=d3e2420-110228

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585

Name:	us-gaap_AssetImpairmentCharges
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Quarterly Financial Data - Schedule of Quarterly Financial Information (Parenthetical) (Detail) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Jun. 30, 2016	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly Financial Data [Line Items]
Asset impairment charge			$ 697	$ 865	$ 228
CNA Financial [Member]
Quarterly Financial Data [Line Items]
Charge related to recognition of premium deficiency and small deficiency in claim reserves		$ 177
Diamond Offshore Drilling, Inc. [Member]
Quarterly Financial Data [Line Items]
Asset impairment charge	$ 267	$ 182