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Reinsurance - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]      
Reinsurance ceded $ 322.7us-gaap_ReinsuranceEffectOnClaimsAndBenefitsIncurredAmountCeded $ 347.0us-gaap_ReinsuranceEffectOnClaimsAndBenefitsIncurredAmountCeded $ 230.7us-gaap_ReinsuranceEffectOnClaimsAndBenefitsIncurredAmountCeded
State Reinsurance Plan      
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]      
Percentage of Ceded Premiums 97.00%pgr_PercentageOfCededPremiums
/ pgr_StateReinsurancePlansAxis
= pgr_StateReinsurancePlansMember		 97.00%pgr_PercentageOfCededPremiums
/ pgr_StateReinsurancePlansAxis
= pgr_StateReinsurancePlansMember		 98.00%pgr_PercentageOfCededPremiums
/ pgr_StateReinsurancePlansAxis
= pgr_StateReinsurancePlansMember
State Reinsurance Plan | Michigan Catastrophic Claims Association And North Carolina Reinsurance Facility      
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]      
Percentage of Ceded Premiums 75.00%pgr_PercentageOfCededPremiums
/ pgr_StateProvidedReinsuranceFacilityAxis
= pgr_MichiganCatastrophicClaimsAssociationAndNorthCarolinaReinsuranceFacilityMember
/ pgr_StateReinsurancePlansAxis
= pgr_StateReinsurancePlansMember		 77.00%pgr_PercentageOfCededPremiums
/ pgr_StateProvidedReinsuranceFacilityAxis
= pgr_MichiganCatastrophicClaimsAssociationAndNorthCarolinaReinsuranceFacilityMember
/ pgr_StateReinsurancePlansAxis
= pgr_StateReinsurancePlansMember		 80.00%pgr_PercentageOfCededPremiums
/ pgr_StateProvidedReinsuranceFacilityAxis
= pgr_MichiganCatastrophicClaimsAssociationAndNorthCarolinaReinsuranceFacilityMember
/ pgr_StateReinsurancePlansAxis
= pgr_StateReinsurancePlansMember