Employee Benefit Plans Assets Held in Deferral Plan Irrevocable Grantor Trust Account (Parenthetical) (Detail) - shares shares in Millions	Dec. 31, 2015	Dec. 31, 2014
Progressive common shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common shares held in Deferral Plan Irrevocable Grantor Trust account to be distributed in-kind	4.4	3.6

The maximum number of shares authorized for issuance under the deferred compensation arrangement as of the balance sheet date.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

Name:	us-gaap_DeferredCompensationArrangementWithIndividualSharesAuthorizedForIssuance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant