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Segment Information - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Segment Reporting Information [Line Items]      
Net premiums earned $ 18,398.5us-gaap_PremiumsEarnedNetPropertyAndCasualty $ 17,103.4us-gaap_PremiumsEarnedNetPropertyAndCasualty $ 16,018.0us-gaap_PremiumsEarnedNetPropertyAndCasualty
Depreciation 97.1us-gaap_Depreciation 101.3us-gaap_Depreciation 94.4us-gaap_Depreciation
Underwriting Operations | Personal Lines | Agency Channel | Lower Limit      
Segment Reporting Information [Line Items]      
Independent insurance agencies and brokerages 35,000pgr_IndependentInsuranceAgenciesAndBrokerages
/ us-gaap_ConsolidationItemsAxis
= pgr_UnderwritingOperationsMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember
/ us-gaap_SubsegmentsAxis
= pgr_AgencyChannelMember		    
Australia      
Segment Reporting Information [Line Items]      
Net premiums earned $ 17.1us-gaap_PremiumsEarnedNetPropertyAndCasualty
/ us-gaap_StatementGeographicalAxis
= country_AU		 $ 13.0us-gaap_PremiumsEarnedNetPropertyAndCasualty
/ us-gaap_StatementGeographicalAxis
= country_AU		 $ 7.1us-gaap_PremiumsEarnedNetPropertyAndCasualty
/ us-gaap_StatementGeographicalAxis
= country_AU