Segment Information Operating Results (Detail) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting Information [Line Items]
Revenues	$ 6,791.8	$ 5,935.0	$ 19,719.2	$ 17,311.8
Pretax Profit (Loss)	251.4	258.5	1,447.5	933.2
Amortization of intangible assets	17.2	15.5	48.2	46.6
Personal Lines \| Agency \| Underwriting operations
Segment Reporting Information [Line Items]
Revenues	2,840.0	2,474.3	8,224.0	7,245.5
Pretax Profit (Loss)	69.5	98.6	524.7	354.5
Personal Lines \| Direct \| Underwriting operations
Segment Reporting Information [Line Items]
Revenues	2,734.8	2,391.2	7,908.5	6,946.7
Pretax Profit (Loss)	128.7	84.4	466.7	237.5
Operating Segments \| Underwriting operations
Segment Reporting Information [Line Items]
Revenues	6,544.0	5,723.4	18,884.0	16,602.6
Pretax Profit (Loss)	172.0	197.0	1,100.0	659.4
Operating Segments \| Personal Lines \| Underwriting operations
Segment Reporting Information [Line Items]
Revenues	5,574.8	4,865.5	16,132.5	14,192.2
Pretax Profit (Loss)	$ 198.2	$ 183.0	$ 991.4	$ 592.0
Personal auto insurance percentage of the total personal lines segment net premiums earned	93.00%	92.00%	93.00%	92.00%
Operating Segments \| Commercial Lines \| Underwriting operations
Segment Reporting Information [Line Items]
Revenues	$ 714.0	$ 630.2	$ 2,031.2	$ 1,772.4
Pretax Profit (Loss)	42.8	4.4	166.4	96.7
Operating Segments \| Property \| Underwriting operations
Segment Reporting Information [Line Items]
Revenues	255.2	227.7	720.3	638.0
Pretax Profit (Loss)	(69.0)	10.4	(57.5)	(27.7)
Amortization of intangible assets	17.2	15.5	48.2	46.6
Operating Segments \| Other Indemnity \| Underwriting operations
Segment Reporting Information [Line Items]
Revenues	0.0	0.0	0.0	0.0
Pretax Profit (Loss)	0.0	(0.8)	(0.3)	(1.6)
Segment Reconciling Items \| Fees and other revenues
Segment Reporting Information [Line Items]
Revenues	96.3	86.8	270.3	248.2
Segment Reconciling Items \| Service businesses
Segment Reporting Information [Line Items]
Revenues	33.3	26.2	94.5	77.7
Pretax Profit (Loss)	4.4	3.0	12.7	9.2
Segment Reconciling Items \| Investment income
Segment Reporting Information [Line Items]
Revenues	118.2	98.6	470.2	381.7
Pretax Profit (Loss)	112.4	93.8	452.2	366.8
Segment Reconciling Items \| Gains on extinguishment of debt
Segment Reporting Information [Line Items]
Revenues	0.0	0.0	0.2	1.6
Pretax Profit (Loss)	0.0	0.0	0.2	1.6
Segment Reconciling Items \| Interest expense
Segment Reporting Information [Line Items]
Pretax Profit (Loss)	$ (37.4)	$ (35.3)	$ (117.6)	$ (103.8)

Percentage of segment revenue attributable to personal auto insurance.

No definition available.

Name:	pgr_PercentageOfSegmentRevenueAttributableToPersonalAutoInsurance
Namespace Prefix:	pgr_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6388964&loc=d3e16225-109274

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275

+ Details

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

- Definition

Amount of income (loss) from continuing operations before deduction of income tax expense (benefit) and income (loss) attributable to noncontrolling interest, and addition of income (loss) from equity method investments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(h)(1)(i))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

+ Details

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

- Definition

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

+ Details

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

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=pgr_PersonalLinesSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsegmentsAxis=pgr_AgencyChannelMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ProductOrServiceAxis=pgr_UnderwritingOperationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsegmentsAxis=pgr_DirectChannelMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConsolidationItemsAxis=us-gaap_OperatingSegmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=pgr_CommercialLinesSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=pgr_PropertySegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=pgr_OtherIndemnityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConsolidationItemsAxis=us-gaap_MaterialReconcilingItemsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ProductOrServiceAxis=pgr_FeesAndOtherRevenuesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ProductOrServiceAxis=pgr_NonInsuranceServiceBusinessMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeStatementLocationAxis=us-gaap_InvestmentIncomeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeStatementLocationAxis=pgr_GainsLossesOnExtinguishmentOfDebtNetOfExpensesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeStatementLocationAxis=us-gaap_InterestExpenseMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: