Investments OTTI Credit Losses Recognized in Earnings (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Beginning balance	$ 0.5	$ 11.5	$ 0.5	$ 11.5
Reductions for securities sold/matured	0.0	(11.4)	0.0	(11.2)
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Changes in Cash Flows	0.3	0.2	0.3	0.0
Ending balance	0.8	0.3	0.8	0.3
Residential mortgage-backed securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Beginning balance	0.0	11.4	0.0	11.1
Reductions for securities sold/matured	0.0	(11.4)	0.0	(10.9)
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Changes in Cash Flows	0.3	0.2	0.3	0.0
Ending balance	0.3	0.2	0.3	0.2
Commercial mortgage-backed securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Beginning balance	0.5	0.1	0.5	0.4
Reductions for securities sold/matured	0.0	0.0	0.0	(0.3)
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Changes in Cash Flows	0.0	0.0	0.0	0.0
Ending balance	$ 0.5	$ 0.1	$ 0.5	$ 0.1

Current period changes in the cumulative amount of credit losses recognized in earnings for an other than temporary impairment (OTTI) of a debt security held due to changes in the cash flows expected to be collected and recognized over the remaining lives of the securities.

No definition available.

+ Details

Name:	pgr_OtherthanTemporaryImpairmentCreditLossesRecognizedinEarningsChangesinCashFlows
Namespace Prefix:	pgr_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The cumulative amount of credit losses recognized in earnings related to debt securities held for which a portion of an other than temporary impairment (OTTI) was recognized in other comprehensive income (a component of shareholders' equity).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 8B
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=SL6284393-111563

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 8B
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=SL6284393-111563

+ Details

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

- Definition

This item represents reductions in the cumulative amount of credit losses recognized in earnings for an other than temporary impairment (OTTI) of a debt security because of the sale of impaired securities during the period.

+ References

+ Details

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

- Definition

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

+ References

No definition available.

+ Details

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

- Details

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

- Details

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