Fair Value Summary of Changes in Fair Value Associated with Level 3 Assets (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning balance	$ 174.9	$ 53.6	$ 54.8	$ 43.4
Calls/ Maturities/ Paydowns	0.0	0.0	0.0	0.0
Purchases	3.0	2.4	71.7	27.4
Sales	0.0	0.0	0.0	0.0
Net Realized (Gain)/Loss on Sales	0.0	0.0	(4.5)	0.0
Change in Valuation	0.0	0.0	55.9	(14.8)
Net Transfers In (Out)	0.0	0.0	0.0	0.0
Fair value, ending balance	177.9	56.0	177.9	56.0
Total equity securities \| Financials \| Nonredeemable preferred stocks
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning balance	76.4	38.1	10.0	27.1
Calls/ Maturities/ Paydowns	0.0	(25.0)	0.0	(25.0)
Purchases	0.0	0.0	60.2	25.0
Sales	0.0	0.0	0.0	0.0
Net Realized (Gain)/Loss on Sales	0.0	0.0	0.0	0.0
Change in Valuation	0.0	0.0	6.2	(14.0)
Net Transfers In (Out)	0.0	0.0	0.0	0.0
Fair value, ending balance	76.4	13.1	76.4	13.1
Total equity securities \| Industrials \| Nonredeemable preferred stocks
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning balance	34.4	15.2	16.7	16.0
Calls/ Maturities/ Paydowns	0.0	0.0	0.0	0.0
Purchases	0.0	0.0	0.0	0.0
Sales	0.0	0.0	0.0	0.0
Net Realized (Gain)/Loss on Sales	0.0	0.0	(4.5)	0.0
Change in Valuation	0.0	0.0	22.2	(0.8)
Net Transfers In (Out)	0.0	0.0	0.0	0.0
Fair value, ending balance	34.4	15.2	34.4	15.2
Total equity securities \| Common Stocks, excluding Other Risk \| Common equities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning balance	52.5	0.0	25.0	0.0
Calls/ Maturities/ Paydowns	0.0	25.0	0.0	25.0
Purchases	2.0	0.0	2.0	0.0
Sales	0.0	0.0	0.0	0.0
Net Realized (Gain)/Loss on Sales	0.0	0.0	0.0	0.0
Change in Valuation	0.0	0.0	27.5	0.0
Net Transfers In (Out)	0.0	0.0	0.0	0.0
Fair value, ending balance	54.5	25.0	54.5	25.0
Total equity securities \| Other risk investments \| Common equities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning balance	11.6	0.3	3.1	0.3
Calls/ Maturities/ Paydowns	0.0	0.0	0.0	0.0
Purchases	1.0	2.4	9.5	2.4
Sales	0.0	0.0	0.0	0.0
Net Realized (Gain)/Loss on Sales	0.0	0.0	0.0	0.0
Change in Valuation	0.0	0.0	0.0	0.0
Net Transfers In (Out)	0.0	0.0	0.0	0.0
Fair value, ending balance	$ 12.6	$ 2.7	$ 12.6	$ 2.7

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

No definition available.

Name:	us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of gain (loss) recognized in income from asset measured at fair value on recurring basis using unobservable input (level 3).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=123874694&loc=d3e19207-110258

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of increase (decrease) of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=123874694&loc=d3e19207-110258

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPeriodIncreaseDecrease
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of purchases of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=123874694&loc=d3e19207-110258

+ Details

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

- Definition

Amount of sale of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=123874694&loc=d3e19207-110258

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of settlement of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=123874694&loc=d3e19207-110258

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of transfer of financial instrument classified as an asset into (out of) level 3 of the fair value hierarchy.

+ References

No definition available.

+ Details

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

- Definition

Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_EquitySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	pgr_InvestmentCategoryAxis=us-gaap_BanksTrustAndInsuranceEquitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_NonredeemablePreferredStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	pgr_InvestmentCategoryAxis=us-gaap_IndustrialMiscellaneousAndAllOthersMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	pgr_InvestmentCategoryAxis=us-gaap_CommonStocksByIndustryMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CommonStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	pgr_InvestmentCategoryAxis=pgr_OtherRiskInvestmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: