The Progressive Corporation (PGR) 10-K 2 Mar 15 2014 FY Annual report Financial data

Document_and_Entity_Informatio

Document and Entity Information (USD $)	12 Months Ended
	Dec. 31, 2014	Jan. 30, 2015	Jun. 30, 2014
Document Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	FALSE
Document Period End Date	31-Dec-14
Document Fiscal Year Focus	2014
Document Fiscal Period Focus	FY
Trading Symbol	PGR
Entity Registrant Name	PROGRESSIVE CORP/OH/
Entity Central Index Key	80661
Current Fiscal Year End Date	-19
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		588,932,479
Entity Public Float			$14,825,867,953

Consolidated_Statements_of_Com

Consolidated Statements of Comprehensive Income (USD $)	12 Months Ended
In Millions, except Per Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenues
Net premiums earned	$18,398.50	$17,103.40	$16,018
Investment income	408.4	422	443
Other-than-temporary impairment (OTTI) losses:
Total OTTI losses	-7.9	-6	-7.3
Non-credit losses, net of credit losses recognized on previously recorded non-credit OTTI losses	0	-0.1	-0.7
Net impairment losses recognized in earnings	-7.9	-6.1	-8
Net realized gains (losses) on securities	232.1	324.5	314.8
Total net realized gains (losses) on securities	224.2	318.4	306.8
Fees and other revenues	309.1	291.8	281.8
Service revenues	56	39.6	36.1
Gains (losses) on extinguishment of debt	-4.8	-4.3	-1.8
Total revenues	19,391.40	18,170.90	17,083.90
Expenses
Losses and loss adjustment expenses	13,306.20	12,472.40	11,948
Policy acquisition costs	1,524	1,451.80	1,436.60
Other underwriting expenses	2,467.10	2,350.90	2,206.30
Investment expenses	18.9	18.8	15.4
Service expenses	50.9	38.8	36.1
Interest expense	116.9	118.2	123.8
Total expenses	17,484	16,450.90	15,766.20
Net Income
Income before income taxes	1,907.40	1,720	1,317.70
Provision for income taxes	626.4	554.6	415.4
Net income	1,281	1,165.40	902.3
Net unrealized gains (losses) on securities:
Net non-credit related OTTI losses, adjusted for valuation changes	0	0.3	5.1
Other net unrealized gains (losses) on securities	74.9	84	174.8
Total net unrealized gains (losses) on securities	74.9	84.3	179.9
Net unrealized gains on forecasted transactions	-2.6	-2	-1.8
Foreign currency translation adjustment	-0.9	-1.6	0.4
Other comprehensive income (loss)	71.4	80.7	178.5
Comprehensive income	$1,352.40	$1,246.10	$1,080.80
Computation of Net Income Per Share
Average shares outstanding - Basic (shares)	590.6	599.1	603.3
Net effect of dilutive stock-based compensation (shares)	4.2	4.5	4.5
Total equivalent shares - Diluted (shares)	594.8	603.6	607.8
Basic: Net income per share (USD per share)	$2.17	$1.95	$1.50
Diluted: Net income per share (USD per share)	$2.15	$1.93	$1.48

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Dec. 31, 2014		Dec. 31, 2013
In Millions, unless otherwise specified
Investments - Available-for-sale, at fair value:
Fixed maturities (amortized cost: $13,374.2 and $13,415.3)	$13,549.20		$13,540.40
Equity securities:
Nonredeemable preferred stocks (cost: $590.4 and $445.7)	827.5		711.2
Common equities (cost: $1,289.2 and $1,451.1)	2,492.30		2,530.50
Short-term investments (amortized cost: $2,149.0 and $1,272.6)	2,149		1,272.60
Total investments at fair value	19,018	[1],[2]	18,054.70	[1],[2]
Cash	108.4		75.1
Accrued investment income	87.3		89.8
Premiums receivable, net of allowance for doubtful accounts of $152.2 and $142.4	3,537.50		3,310.70
Reinsurance recoverables, including $46.0 and $44.3 on paid losses and loss adjustment expenses	1,231.90		1,090.20
Prepaid reinsurance premiums	85.3		74.9
Deferred acquisition costs	457.2		447.6
Property and equipment, net of accumulated depreciation of $731.0 and $680.4	960.6		960.9
Other assets	301.4		304.3
Total assets	25,787.60		24,408.20
Liabilities and Shareholders' Equity
Unearned premiums	5,440.10		5,174.50
Loss and loss adjustment expense reserves	8,857.40		8,479.70
Net deferred income taxes	98.9		28.4
Dividends payable	404.1		890.2
Accounts payable, accrued expenses, and other liabilities	1,893.80	[3]	1,785	[3]
Debt	2,164.70	[4]	1,860.90	[4]
Total liabilities	18,859		18,218.70
Common shares, $1.00 par value (authorized 900.0; issued 797.6, including treasury shares of 209.8 and 201.8)	587.8		595.8
Paid-in capital	1,184.30		1,142
Retained earnings	4,133.40		3,500
Accumulated other comprehensive income, net of tax:
Net non-credit related OTTI losses, adjusted for valuation changes	0		0
Other net unrealized gains (losses) on securities	1,021.90		947
Total net unrealized gains (losses) on securities	1,021.90		947
Net unrealized gains on forecasted transactions	1.5		4.1
Foreign currency translation adjustment	-0.3		0.6
Total accumulated other comprehensive income	1,023.10		951.7
Total shareholders' equity	6,928.60		6,189.50
Total liabilities and shareholders' equity	$25,787.60		$24,408.20
[1]	The total fair value of the portfolio included $1.9 billion and $1.8 billion at December 31, 2014 and 2013, respectively, of securities held in a consolidated, non-insurance subsidiary of the holding company, net of any unsettled security transactions.
[2]	Our portfolio reflects the effect of unsettled security transactions and collateral on open derivative positions; at December 31, 2014, $31.3 million was included in "other liabilities," compared to $61.3 million at December 31, 2013.
[3]	See Note 12 – Litigation and Note 13 – Commitments and Contingencies for further discussion.
[4]	Consists of long-term debt. See Note 4 – Debt for further discussion.

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Parenthetical) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, except Per Share data, unless otherwise specified
Statement of Financial Position [Abstract]
Fixed maturities, amortized cost	$13,374.20	$13,415.30
Nonredeemable preferred stocks, cost	590.4	445.7
Common equities, cost	1,289.20	1,451.10
Short-term investments, amortized cost	2,149	1,272.60
Premiums receivable, allowance for doubtful accounts	152.2	142.4
Reinsurance recoverables, paid losses and loss adjustment expenses	46	44.3
Property and equipment, accumulated depreciation	$731	$680.40
Common Shares, par value (USD per share)	$1	$1
Common Shares, authorized (shares)	900	900
Common Shares, issued (shares)	797.6	797.6
Common Shares, treasury shares (shares)	209.8	201.8

Consolidated_Statements_of_Cha

Consolidated Statements of Changes in Shareholders' Equity (USD $)		Total	Common Shares, $1.00 Par Value	Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income, Net of Tax
In Millions
Balance, Beginning of year at Dec. 31, 2011			$613	$1,006.20	$3,495	$692.50
Stock options exercised			0.1	0.4
Net income		902.3			902.3
Other comprehensive income (loss)		178.5				178.5
Tax benefit from exercise/vesting of equity-based compensation				5.8
Treasury shares purchased	[1]		-8.6	-14.5	-151.1
Net restricted equity awards (issued) (vested) forfeited			0.1	-0.1
Cash dividends declared on common shares ($0.6862, $1.4929, and $1.2845 per share)					-772.5
Amortization of equity-based compensation				62.4
Reinvested dividends on restricted stock units				11.2	-11.2
Other				5.6	-8.1
Balance, End of year at Dec. 31, 2012		6,007	604.6	1,077	3,454.40	871
Stock options exercised			0	0
Net income		1,165.40			1,165.40
Other comprehensive income (loss)		80.7				80.7
Tax benefit from exercise/vesting of equity-based compensation				10.3
Treasury shares purchased	[1]		-11	-20.4	-242
Net restricted equity awards (issued) (vested) forfeited			2.2	-2.2
Cash dividends declared on common shares ($0.6862, $1.4929, and $1.2845 per share)					-889.2
Amortization of equity-based compensation				64.9
Reinvested dividends on restricted stock units				12.4	-12.4
Other				0	23.8
Balance, End of year at Dec. 31, 2013		6,189.50	595.8	1,142	3,500	951.7
Stock options exercised			0	0
Net income		1,281			1,281
Other comprehensive income (loss)		71.4				71.4
Tax benefit from exercise/vesting of equity-based compensation				12.8
Treasury shares purchased	[1]		-11.1	-21.6	-238.7
Net restricted equity awards (issued) (vested) forfeited			3.1	-3.1
Cash dividends declared on common shares ($0.6862, $1.4929, and $1.2845 per share)					-402.6
Amortization of equity-based compensation				51.4
Reinvested dividends on restricted stock units				2.8	-2.8
Other				0	-3.5
Balance, End of year at Dec. 31, 2014		$6,928.60	$587.80	$1,184.30	$4,133.40	$1,023.10
[1]	In December 2013, we purchased 4.0 million shares at a price of $25.50 per share in a privately negotiated transaction with the "Peter B. Lewis Trust under Agreement dated December 21, 1994, as modified." Mr. Lewis was our non-executive Chairman of the Board until his death in November 2013.

Consolidated_Statements_of_Cha1

Consolidated Statements of Changes in Shareholders' Equity (Parenthetical) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Number of shares acquired in a privately negotiated transaction		4,000,000
Treasury Stock Acquired Cost per Share Privately Negotiated Transaction		$25.50
Retained Earnings
Cash dividends declared on common shares, per share	$0.69	$1.49	$1.28
Serial Preferred Stock
Preference Shares authorized	20,000,000
Preference Shares issued	0
Preferred Shares outstanding	0
Voting Preferred Stock
Preference Shares authorized	5,000,000
Preference Shares issued	0

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash Flows From Operating Activities
Net income	$1,281	$1,165.40	$902.30
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	97.1	101.3	94.4
Amortization of fixed-income securities	78.2	134	186.7
Amortization of equity-based compensation	51.4	64.9	63.4
Net realized (gains) losses on securities	-224.2	-318.4	-306.8
Net (gains) losses on disposition of property and equipment	5.4	5.6	7.1
(Gains) losses on extinguishment of debt	4.8	4.3	1.8
Changes in:
Premiums receivable	-227.1	-127.4	-253.8
Reinsurance recoverables	-141.7	-189.2	-83
Prepaid reinsurance premiums	-10.4	-8.6	3.5
Deferred acquisition costs	-9.6	-13.1	-0.9
Income taxes	97.5	57.8	19.8
Unearned premiums	266.4	244.8	351.1
Loss and loss adjustment expense reserves	378	641.6	592.6
Accounts payable, accrued expenses, and other liabilities	92	165	123.6
Other, net	-13.2	-28.1	-10.4
Net cash provided by operating activities	1,725.60	1,899.90	1,691.40
Purchases:
Fixed maturities	-7,967.50	-7,100.60	-5,199.20
Equity securities	-369.7	-322.2	-463.1
Sales:
Fixed maturities	5,637.50	3,083.90	3,705.60
Equity securities	560.1	369.2	793
Maturities, paydowns, calls, and other:
Fixed maturities	2,296.60	1,859.60	1,488.90
Equity securities	14.3	21.5	16
Net sales (purchases) of short-term investments	-876	716.6	-438.2
Net unsettled security transactions	-30	152.2	-44
Purchases of property and equipment	-108.1	-140.4	-127.7
Sales of property and equipment	5.9	3.7	3.8
Net cash provided by (used in) investing activities	-836.9	-1,356.50	-264.9
Cash Flows From Financing Activities
Proceeds from exercise of stock options	0	0	0.5
Tax benefit from exercise/vesting of equity-based compensation	12.8	10.3	5.8
Net proceeds from debt issuance	344.7	0	0
Payment of debt	0	-150	-350
Reacquisition of debt	-48.9	-58.1	-32.5
Dividends paid to shareholders	-892.6	-175.6	-853.7
Acquisition of treasury shares	-271.4	-273.4	-174.2
Net cash used in financing activities	-855.4	-646.8	-1,404.10
Effect of exchange rate changes on cash	0	-0.6	1
Increase (decrease) in cash	33.3	-104	23.4
Cash, Beginning of year	75.1	179.1	155.7
Cash, End of year	$108.40	$75.10	$179.10

SCHEDULE_I_Summary_Of_Investme

SCHEDULE I - Summary Of Investments - Other Than Investments in Related Parties	12 Months Ended
	Dec. 31, 2014
Text Block [Abstract]
SCHEDULE I - Summary Of Investments - Other Than Investments In Related Parties	SCHEDULE I — SUMMARY OF INVESTMENTS — OTHER THAN INVESTMENTS IN RELATED PARTIES
	THE PROGRESSIVE CORPORATION AND SUBSIDIARIES
	(millions)
		December 31, 2014
	Type of Investment	Cost		Fair Value		Amount At
						Which Shown
						In The
						Balance Sheet
	Available-for-sale
	Fixed maturities:
	Bonds:
	United States Government and government agencies and authorities	$	2,641.10	$	2,667.10	$	2,667.10
	States, municipalities, and political subdivisions	2,095.70		2,139.20		2,139.20
	Foreign government obligations	14.2		14.2		14.2
	Public utilities	63.1		66.6		66.6
	Corporate and other debt securities	2,750.80		2,770.10		2,770.10
	Asset-backed securities	5,549.10		5,612.80		5,612.80
	Redeemable preferred stocks	260.2		279.2		279.2
	Total fixed maturities	13,374.20		13,549.20		13,549.20
	Equity securities:
	Common stocks:
	Public utilities	95		143.3		143.3
	Banks, trusts, and insurance companies	220.1		438.4		438.4
	Industrial, miscellaneous, and all other	974.1		1,910.60		1,910.60
	Nonredeemable preferred stocks	590.4		827.5		827.5
	Total equity securities	1,879.60		3,319.80		3,319.80
	Short-term investments1	2,149.00		2,149.00		2,149.00
	Total investments	$	17,402.80	$	19,018.00	$	19,018.00
	1 Includes $5.7 million in treasury bills issued by the Australian government.
	Progressive did not have any securities of any one issuer, excluding U.S. government obligations, with an aggregate cost or fair value exceeding 10% of total shareholders’ equity at December 31, 2014.

SCHEDULE_II_Condensed_Financia

SCHEDULE II - Condensed Financial Information Of Registrant	12 Months Ended
	Dec. 31, 2014
Text Block [Abstract]
SCHEDULE II - Condensed Financial Information Of Registrant	SCHEDULE II — CONDENSED FINANCIAL INFORMATION OF REGISTRANT
	CONDENSED STATEMENTS OF COMPREHENSIVE INCOME
	THE PROGRESSIVE CORPORATION (PARENT COMPANY)
	(millions)
		Years Ended December 31,
		2014				2013				2012
	Revenues
	Dividends from subsidiaries	$	1,000.20			$	1,119.70			$	782.3
	Undistributed income (loss) from subsidiaries	358.3				117.5				193.1
	Equity in net income of subsidiaries*	1,358.50				1,237.20				975.4
	Intercompany investment income*	2.4				2.8				6.1
	Gains (losses) on extinguishment of debt	(4.8		)		(4.3		)		(1.8		)
	Other income1	0				2.6				0
	Total revenues	1,356.10				1,238.30				979.7
	Expenses
	Interest expense	120.2				121.2				126.3
	Deferred compensation2	2.8				9.5				5.5
	Other operating costs and expenses	4.4				4				3.7
	Total expenses	127.4				134.7				135.5
	Income before income taxes	1,228.70				1,103.60				844.2
	Benefit for income taxes	(52.3		)		(61.8		)		(58.1		)
	Net income	$	1,281.00			$	1,165.40			$	902.3
	Other comprehensive income	71.4				80.7				178.5
	Comprehensive income	$	1,352.40			$	1,246.10			$	1,080.80
	* Eliminated in consolidation.
	1 Represents gain on net death benefit received on life insurance policies.
	2 See Note 4 – Employee Benefit Plans in these condensed financial statements.
	See notes to condensed financial statements.
	CONDENSED BALANCE SHEETS
	THE PROGRESSIVE CORPORATION (PARENT COMPANY)
	(millions)
		December 31,
		2014				2013
	Assets
	Investment in affiliate	$	5			$	5
	Investment in subsidiaries*	7,423.50				6,923.50
	Receivable from investment subsidiary*	1,677.50				1,648.40
	Intercompany receivable*	413				307.6
	Net deferred income taxes	74.5				69.1
	Other assets	123.9				141.8
	Total Assets	$	9,717.40			$	9,095.40
	Liabilities and Shareholders’ Equity
	Accounts payable, accrued expenses, and other liabilities	$	220			$	154.8
	Dividend payable	404.1				890.2
	Debt	2,164.70				1,860.90
	Total liabilities	2,788.80				2,905.90
	Common shares, $1.00 par value (authorized 900.0; issued 797.6, including treasury shares of 209.8 and 201.8)	587.8				595.8
	Paid-in capital	1,184.30				1,142.00
	Retained earnings	4,133.40				3,500.00
	Total accumulated other comprehensive income	1,023.10				951.7
	Total shareholders’ equity	6,928.60				6,189.50
	Total Liabilities and Shareholders’ Equity	$	9,717.40			$	9,095.40
	*Eliminated in consolidation.
	See notes to condensed financial statements.
	CONDENSED STATEMENTS OF CASH FLOWS
	THE PROGRESSIVE CORPORATION (PARENT COMPANY)
	(millions)
		Years Ended December 31,
		2014				2013				2012
	Cash Flows From Operating Activities:
	Net income	$	1,281.00			$	1,165.40			$	902.3
	Adjustments to reconcile net income to net cash provided by operating activities:
	Undistributed (income) loss from subsidiaries	(358.3		)		(117.5		)		(193.1		)
	Amortization of equity-based compensation	2.2				2.1				2
(Gains) losses on extinguishment of debt	4.8				4.3				1.8
Changes in:
Intercompany receivable	(105.4		)		(11.4		)		(58.6		)
Accounts payable, accrued expenses, and other liabilities	18.2				19.4				0.3
Income taxes	61.1				(55.8		)		21.7
Other, net	0.4				(16.3		)		(9.9		)
Net cash provided by operating activities	904				990.2				666.5
Cash Flows From Investing Activities:
Additional investments in equity securities of consolidated subsidiaries	(21.1		)		(13.9		)		(36.1		)
Investment in affiliate	0				(4.0		)		0
(Paid to) received from investment subsidiary	(29.1		)		(325.5		)		773.7
Net cash provided by (used in) investing activities	(50.2		)		(343.4		)		737.6
Cash Flows From Financing Activities:
Proceeds from exercise of stock options	0				0				0.5
Tax benefit from exercise/vesting of equity-based compensation	12.8				10.3				5.8
Net proceeds from debt issuance	346.3				0				0
Payment of debt	0				(150.0		)		(350.0		)
Reacquisition of debt	(48.9		)		(58.1		)		(32.5		)
Dividends paid to shareholders	(892.6		)		(175.6		)		(853.7		)
Acquisition of treasury shares	(271.4		)		(273.4		)		(174.2		)
Net cash used in financing activities	(853.8		)		(646.8		)		(1,404.1		)
Change in cash	0				0				0
Cash, beginning of year	0				0				0
Cash, end of year	$	0			$	0			$	0
See notes to condensed financial statements.
NOTES TO CONDENSED FINANCIAL STATEMENTS
The accompanying condensed financial statements of The Progressive Corporation (parent company) should be read in conjunction with the consolidated financial statements and notes thereto in the Annual Report to Shareholders of The Progressive Corporation and its subsidiaries, which is included as Exhibit 13 to this Form 10-K.
Note 1. Statements of Cash Flows — For the purpose of the Statements of Cash Flows, cash includes only bank demand deposits. The Progressive Corporation does not hold any cash but has unrestricted access to funds maintained in a non-insurance, investment subsidiary to meet its holding company obligations; at year-end 2014 and 2013, $1.9 billion and $1.8 billion, respectively, of marketable securities were available in this subsidiary. Non-cash activity includes declared but unpaid dividends. For the years ended December 31, we paid the following:
(millions)	2014			2013			2012
Income taxes	$	515		$	497		$	389.1
Interest	116			122.3			135
Note 2. Income Taxes — The Progressive Corporation files a consolidated federal income tax return with all subsidiaries and acts as an agent for the consolidated tax group when making payments to the Internal Revenue Service. The consolidated group’s net income taxes currently payable/recoverable are included in other liabilities/assets, respectively, in the accompanying Condensed Balance Sheets based on the balance at the end of the year. The Progressive Corporation and its subsidiaries have adopted, pursuant to a written agreement, a method of allocating consolidated federal income taxes. Amounts allocated to the subsidiaries under the written agreement are included in “Intercompany Receivable” in the accompanying Condensed Balance Sheets.
Note 3. Debt — The information relating to debt is incorporated by reference from Note 4 – Debt in our Annual Report, which is included as Exhibit 13 to this Form 10-K.
Note 4. Employee Benefit Plans — The information relating to incentive compensation plans and deferred compensation is incorporated by reference from Note 9 – Employee Benefit Plans in our Annual Report, which is included as Exhibit 13 to this Form 10-K.
Note 5. Other Comprehensive Income — On the condensed Statements of Comprehensive Income, other comprehensive income represents activity of the subsidiaries of The Progressive Corporation and includes net unrealized gains (losses) on securities, net unrealized gains on forecasted transactions, and foreign currency translation adjustments.
Note 6. Dividends — The information relating to our dividend policy is incorporated by reference from Note 14 – Dividends in our Annual Report, which is included as Exhibit 13 to this Form 10-K.

SCHEDULE_III_Supplementary_Ins

SCHEDULE III - Supplementary Insurance Information	12 Months Ended
	Dec. 31, 2014
Text Block [Abstract]
SCHEDULE III - Supplementary Insurance Information	SCHEDULE III — SUPPLEMENTARY INSURANCE INFORMATION
	THE PROGRESSIVE CORPORATION AND SUBSIDIARIES
	(millions)
	Segment	Deferred		Future		Unearned premiums1		Other		Premium revenue		Net		Benefits,		Amortization		Other		Net
		policy		policy				policy				investment income1,2		claims,		of deferred		operating expenses		premiums
		acquisition costs1		benefits,				claims						losses, and		policy				written
				losses,				and						settlement expenses		acquisition costs
				claims,				benefits payable1
				and
				loss expenses1
	Year ended December 31, 2014:
	Personal Lines									$	16,561.00			$	12,161.20	$	1,322.90	$	2,262.60	$	16,759.20
	Commercial Lines									1,837.50				1,133.40		201.1		204.2		1,895.40
	Other indemnity									0				11.6		0		0.3		0
	Total	$	457.2	$	8,857.40	$	5,440.10	$	0	$	18,398.50	$	389.5	$	13,306.20	$	1,524.00	$	2,467.10	$	18,654.60
	Year ended December 31, 2013:
	Personal Lines									$	15,341.60			$	11,194.60	$	1,257.50	$	2,149.20	$	15,569.20
	Commercial Lines									1,761.60				1,267.30		194.3		201.2		1,770.50
	Other indemnity									0.2				10.5		0		0.5		0
	Total	$	447.6	$	8,479.70	$	5,174.50	$	0	$	17,103.40	$	403.2	$	12,472.40	$	1,451.80	$	2,350.90	$	17,339.70
	Year ended December 31, 2012:
	Personal Lines									$	14,368.10			$	10,745.30	$	1,250.40	$	2,010.50	$	14,636.80
	Commercial Lines									1,649.00				1,196.60		186.2		195.2		1,735.90
	Other indemnity									0.9				6.1		0		0.6		0
	Total	$	434.5	$	7,838.40	$	4,930.70	$	0	$	16,018.00	$	427.6	$	11,948.00	$	1,436.60	$	2,206.30	$	16,372.70
	1 Progressive does not allocate assets, liabilities, or investment income to operating segments.
	2 Excludes total net realized gains (losses) on securities.

SCHEDULE_IV_Reinsurance

SCHEDULE IV - Reinsurance	12 Months Ended
	Dec. 31, 2014
Text Block [Abstract]
SCHEDULE IV - Reinsurance	SCHEDULE IV — REINSURANCE
	THE PROGRESSIVE CORPORATION AND SUBSIDIARIES
	(millions)
	Year Ended:	Gross Amount		Ceded to		Assumed		Net Amount		Percentage
				Other Companies		From				of Amount
						Other Companies				Assumed to Net
	31-Dec-14
	Premiums earned:
	Property and liability insurance	$	18,648.40	$	249.9	$	0	$	18,398.50	0
	31-Dec-13
	Premiums earned:
	Property and liability insurance	$	17,317.90	$	214.5	$	0	$	17,103.40	0
	31-Dec-12
	Premiums earned:
	Property and liability insurance	$	16,207.60	$	189.6	$	0	$	16,018.00	0

SCHEDULE_VISupplemental_Inform

SCHEDULE VI-Supplemental Information Concerning Property - Casualty Insurance Operations	12 Months Ended
	Dec. 31, 2014
Text Block [Abstract]
SCHEDULE VI-Supplemental Information Concerning Property - Casualty Insurance Operations	SCHEDULE VI — SUPPLEMENTAL INFORMATION CONCERNING PROPERTY - CASUALTY INSURANCE OPERATIONS
	THE PROGRESSIVE CORPORATION AND SUBSIDIARIES
	(millions)
		Losses and Loss Adjustment
		Expenses Incurred Related to
	Year Ended	Current Year		Prior Years			Paid Losses and Loss
							Adjustment Expenses
	31-Dec-14	$	13,330.30	$	(24.1	)	$	13,068.50
	31-Dec-13	$	12,427.30	$	45.1		$	12,014.90
	31-Dec-12	$	11,926.00	$	22		$	11,431.80
	Pursuant to Rule 12-18 of Regulation S-X. See Schedule III for the additional information required in Schedule VI.

Reporting_And_Accounting_Polic

Reporting And Accounting Policies	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Reporting And Accounting Policies	REPORTING AND ACCOUNTING POLICIES
	Nature of Operations  The Progressive Corporation, an insurance holding company formed in 1965, had 53 subsidiaries, one mutual insurance company affiliate, and one limited partnership investment affiliate (collectively the “subsidiaries”) as of December 31, 2014. Our insurance subsidiaries and mutual company affiliate (collectively the Progressive Group of Insurance Companies) provide personal and commercial automobile insurance and other specialty property-casualty insurance and related services. Our Personal Lines segment writes insurance for personal autos and recreational vehicles through both an independent insurance agency channel and a direct channel. Our Commercial Lines segment writes primary liability and physical damage insurance for automobiles and trucks owned and/or operated predominantly by small businesses through both the independent agency and direct channels. We operate our businesses throughout the United States; we also sell personal auto physical damage and property damage liability insurance via the Internet in Australia.
	Basis of Consolidation and Reporting  The accompanying consolidated financial statements include the accounts of The Progressive Corporation, its wholly owned subsidiaries, and its affiliates, in which we have a controlling financial interest. All intercompany accounts and transactions are eliminated in consolidation.
	Estimates  We are required to make estimates and assumptions when preparing our financial statements and accompanying notes in conformity with accounting principles generally accepted in the United States of America (GAAP). As estimates develop into fact (e.g., losses are paid), results may, and will likely, differ from those estimates.
	Investments  Our fixed-maturity securities, equity securities, and short-term investments are accounted for on an available-for-sale basis. See Note 2 – Investments for details regarding the composition of our investment portfolio.
	Fixed-maturity securities include debt securities and redeemable preferred stocks, which may have fixed or variable principal payment schedules, may be held for indefinite periods of time, and may be used as a part of our asset/liability strategy or sold in response to changes in interest rates, anticipated prepayments, risk/reward characteristics, liquidity needs, or other economic factors. These securities are carried at fair value with the corresponding unrealized gains (losses), net of deferred income taxes, reported in accumulated other comprehensive income. Fair values are obtained from recognized pricing services or are quoted by market makers and dealers, with limited exceptions discussed in Note 3 – Fair Value.
	Included in the fixed-maturity portfolio are asset-backed securities. The asset-backed securities are generally accounted for under the retrospective method. The retrospective method recalculates yield assumptions (based on changes in interest rates or cash flow expectations) historically to the inception of the investment holding period, and applies the required adjustment, if any, to the cost basis, with the offset recorded to investment income. The prospective method is used primarily for interest-only securities, non-investment-grade asset-backed securities, and certain asset-backed securities with sub-prime loan exposure or where there is a greater risk of non-performance and where it is possible the initial investment may not be substantially recovered. The prospective method requires a calculation of expected future repayments and resets the yield to allow for future period adjustments; no current period impact to investment income or the security’s cost is made based on the cash flow update. Prepayment assumptions are based on market expectations and are updated quarterly.
	Equity securities include common stocks, nonredeemable preferred stocks, and other risk investments, and are reported at fair values. Changes in fair value of these securities, net of deferred income taxes, are reflected as unrealized gains (losses) in accumulated other comprehensive income. To the extent we hold any foreign equities or foreign currency hedges, any change in value due to exchange rate fluctuations would be limited by foreign currency hedges, if any, and would be recognized in income in the current period.
	Short-term investments may include Eurodollar deposits, commercial paper, repurchase transactions, and other securities expected to mature within one year. In addition, short-term investments can include auction rate securities (i.e., certain municipal bonds and preferred stocks). Due to the nature of auction rate securities, these securities are classified as short-term based upon their expected auction date (generally 7-49 days) rather than on their contractual maturity date (which is greater than one year at original issuance). In the event that an auction fails, the security may need to be reclassified from short-term. Changes in fair value of these securities, net of deferred income taxes, are reflected as unrealized gains (losses) in accumulated other comprehensive income.
	Trading securities are securities bought principally for the purpose of sale in the near term. To the extent we have trading securities, changes in fair value would be recognized in income in the current period. Derivative instruments, which may be used for trading purposes or classified as trading derivatives due to the characteristics of the transaction, are discussed below.
	Derivative instruments may include futures, options, forward positions, foreign currency forwards, interest rate swap agreements, and credit default swaps and may be used in the portfolio for general investment purposes or to hedge the exposure to:
	•	Changes in fair value of an asset or liability (fair value hedge),
	•	Foreign currency of an investment in a foreign operation (foreign currency hedge), or
	•	Variable cash flows of a forecasted transaction (cash flow hedge).
	To the extent we have derivatives held for general investment purposes, these derivative instruments are recognized as either assets or liabilities and measured at fair value, with changes in fair value recognized in income as a component of net realized gains (losses) on securities during the period of change.
	Derivatives designated as hedges are required to be evaluated on established criteria to determine the effectiveness of their correlation to, and ability to reduce the designated risk of, specific securities or transactions. Effectiveness is required to be reassessed regularly. Hedges that are deemed to be effective would be accounted for as follows:
	•	Fair value hedge:  changes in fair value of the hedge, as well as the hedged item, would be recognized in income in the period of change while the hedge is in effect.
	•	Foreign currency hedge:  changes in fair value of the hedge, as well as the hedged item, would be reflected as a change in translation adjustment as part of accumulated other comprehensive income. Gains and losses on the foreign currency hedge would offset the foreign exchange gains and losses on the foreign investment as they are recognized into income.
	•	Cash flow hedge:  changes in fair value of the hedge would be reported as a component of accumulated other comprehensive income and subsequently amortized into earnings over the life of the hedged transaction.
	If a hedge is deemed to become ineffective or discontinued, the following accounting treatment would be applied:
	•	Fair value hedge:  the derivative instrument would continue to be adjusted through income, while the adjustment in the change in value of the hedged item would be reflected as a change in unrealized gains (losses) as part of accumulated other comprehensive income.
	•	Foreign currency hedge:  changes in the value of the hedged item would continue to be reflected as a change in translation adjustment as part of accumulated other comprehensive income, but the derivative instrument would be adjusted through income for the current period.
	•	Cash flow hedge:  changes in fair value of the derivative instrument would be reported in income for the current period.
	For all derivative positions, net cash requirements are limited to changes in fair values, which may vary resulting from changes in interest rates, currency exchange rates, and other factors. Exposure to credit risk is limited to the carrying value; collateral may be required to limit credit risk. We have elected not to offset fair value amounts that arise from derivative positions with the same counterparty under a master netting arrangement.
	Investment securities are exposed to various risks such as interest rate, market, credit, and liquidity risk. Fair values of securities fluctuate based on the nature and magnitude of changing market conditions; significant changes in market conditions could materially affect the portfolio’s value in the near term. We regularly monitor our portfolio for price changes, which might indicate potential impairments, and perform detailed reviews of securities with unrealized losses. In such cases, changes in fair value are evaluated to determine the extent to which such changes are attributable to: (i) fundamental factors specific to the issuer, such as financial condition, business prospects, or other factors, (ii) market-related factors, such as interest rates or equity market declines, or (iii) credit-related losses, where the present value of cash flows expected to be collected are lower than the amortized cost basis of the security.
	We analyze our debt securities that are in a loss position to determine if we intend to sell, or if it is more likely than not that we will be required to sell, the security prior to recovery and, if so, we write down the security to its current fair value, with the entire amount of the write-down recorded to earnings. To the extent that it is more likely than not that we will hold the debt security until recovery (which could be maturity), we determine if any of the decline in value is due to a credit loss (i.e., where the present value of future cash flows expected to be collected is lower than the amortized cost basis of the security) and, if so, we recognize that portion of the impairment as a component of net realized gains (losses) in the comprehensive income statement, with the difference (i.e., non-credit related impairment) recognized as part of our net unrealized gains (losses) in accumulated other comprehensive income. When an equity security (common equity and nonredeemable preferred stock) in our investment portfolio has an unrealized loss in fair value that is deemed to be other-than-temporary, we reduce the book value of such security to its current fair value, recognizing the decline as a realized loss in the comprehensive income statement. Any future changes in fair value, either increases or decreases, are reflected as changes in unrealized gains (losses) as part of accumulated other comprehensive income.
	Investment income consists of interest, dividends, and amortization. In addition to the discussion above for asset-backed securities, interest is recognized on an accrual basis using the effective yield method. Depending on the nature of the equity instruments, dividends are recorded at either the ex-dividend date or on an accrual basis.
	Realized gains (losses) on securities are computed based on the first-in first-out method and include write-downs on available-for-sale securities considered to have other-than-temporary declines in fair value (excluding non-credit related impairments), as well as holding period valuation changes on derivatives, trading securities, and hybrid instruments (e.g., securities with embedded options, where the option is a feature of the overall change in the value of the instrument).
	Insurance Premiums and Receivables  Insurance premiums written are earned into income on a pro rata basis over the period of risk, based on a daily earnings convention. Accordingly, unearned premiums represent the portion of premiums written that are applicable to the unexpired risk. We provide insurance and related services to individuals and small commercial accounts and offer a variety of payment plans. Generally, premiums are collected prior to providing risk coverage, minimizing our exposure to credit risk. We perform a policy level evaluation to determine the extent to which the premiums receivable balance exceeds the unearned premiums balance. We then age this exposure to establish an allowance for doubtful accounts based on prior experience.
	Deferred Acquisition Costs  Deferred acquisition costs include commissions, premium taxes, and other variable underwriting and direct sales costs incurred in connection with the successful acquisition or renewal of insurance contracts. These acquisition costs are deferred and amortized over the policy period in which the related premiums are earned. We consider anticipated investment income in determining the recoverability of these costs. Management believes that these costs will be fully recoverable in the near term.
	We do not defer any advertising costs. Total advertising costs, which are expensed as incurred, for the years ended December 31, were:
	(millions)	Advertising Costs
	2014	$	681.8
	2013	619.3
	2012	546.8
	Loss and Loss Adjustment Expense Reserves  Loss reserves represent the estimated liability on claims reported to us, plus reserves for losses incurred but not recorded (IBNR). These estimates are reported net of amounts estimated to be recoverable from salvage and subrogation. Loss adjustment expense reserves represent the estimated expenses required to settle these claims and losses. The methods of making estimates and establishing these reserves are reviewed regularly, and resulting adjustments are reflected in income in the current period. Such loss and loss adjustment expense reserves are susceptible to change in the near term.
	Reinsurance  Our reinsurance transactions primarily include premiums ceded to state-provided reinsurance facilities (e.g., Michigan Catastrophic Claims Association and North Carolina Reinsurance Facility) and premiums written under state-mandated involuntary plans for commercial vehicles (Commercial Auto Insurance Procedures/Plans – “CAIP”). Prepaid reinsurance premiums are earned on a pro rata basis over the period of risk, based on a daily earnings convention, which is consistent with premiums written. See Note 7 – Reinsurance for further discussion.
	Income Taxes  The income tax provision is calculated under the balance sheet approach. Deferred tax assets and liabilities are recorded based on the difference between the financial statement and tax bases of assets and liabilities at the enacted tax rates. The principal items giving rise to such differences are investment securities (e.g., net unrealized gains (losses), write-downs on securities determined to be other-than-temporarily impaired, and derivative instruments), loss and loss adjustment expense reserves, unearned premiums reserves, deferred acquisition costs, property and equipment, and non-deductible accruals. We review our deferred tax assets regularly for recoverability. See Note 5 – Income Taxes for further discussion.
	Property and Equipment  Property and equipment are recorded at cost, less accumulated depreciation, and include capitalized software developed or acquired for internal use. Depreciation is recognized over the estimated useful lives of the assets using accelerated methods for computer equipment and the straight-line method for all other fixed assets. The useful life for computer equipment and laptop computers is 3 years. The useful lives range from 7 to 40 years for buildings, improvements, and integrated components and 3 to 15 years for all other property and equipment. Land and buildings comprised 77% and 76% of total property and equipment at December 31, 2014 and 2013, respectively.
	During 2014, decisions were made to sell one property originally purchased for a future Service Center site. At December 31, 2014, included in other assets in the consolidated balance sheets is $8.7 million of "held for sale" property, which represents the fair value of this property less the estimated costs to sell.
	Total capitalized interest, which primarily relates to capitalized software projects, for the years ended December 31, was:
	(millions)	Capitalized
		Interest
	2014	$	1.3
	2013	0.8
	2012	0.3
	Guaranty Fund Assessments  We are subject to state guaranty fund assessments, which provide for the payment of covered claims or other insurance obligations of insurance companies deemed insolvent. These assessments are accrued after a formal determination of insolvency has occurred, and we have written the premiums on which the assessments will be based.
	Fees and Other Revenues  Fees and other revenues primarily represent fees collected from policyholders relating to installment charges in accordance with our bill plans, as well as late payment and insufficient funds fees. Other revenues may include revenue from the sale of tax credits, rental income, and other revenue transactions.
	Service Revenues and Expenses  Our service businesses provide insurance-related services. Service revenues generated from processing business for involuntary CAIP plans are earned on a pro rata basis over the term of the related policies. Service expenses related to these CAIP plans include acquisition expenses, which are deferred and amortized over the period in which the related revenues are earned. Other service business revenues and expenses are recorded in the period in which they are earned or incurred.
	Equity-Based Compensation  We currently issue time-based and performance-based restricted stock unit awards to key members of management as our form of equity compensation, and time-based restricted stock awards to non-employee directors. Prior to 2010, we issued restricted stock awards, instead of restricted stock unit awards, to employees. Collectively, we refer to these awards as “restricted equity awards.” We currently do not issue stock options as a form of equity compensation, and no such awards remain outstanding. Compensation expense for time-based restricted equity awards with installment vesting is recognized over each respective vesting period. For performance-based restricted equity awards, compensation expense is recognized over the respective estimated vesting periods. Dividend equivalent units are credited
	to outstanding restricted units awards, both time-based and performance-based, at the time a dividend is paid to shareholders.
	We record an estimate for expected forfeitures of restricted equity awards based on our historical forfeiture rates. In addition, we shorten the vesting periods of certain restricted equity awards based on the “qualified retirement” provisions in our incentive compensation plans, under which (among other provisions) the vesting of 50% of outstanding time-based restricted equity awards will accelerate upon retirement if the participant is 55 years of age or older and satisfies certain years-of-service requirements. For time-based awards granted after February 2013, we modified our "qualified retirement" provisions to vest and distribute 50% of the unvested portion of the award upon reaching eligibility for a qualified retirement and shortly after the grant date for each subsequent award.
	The total compensation expense recognized for our equity-based compensation for the years ended December 31, was:
	(millions)	2014		2013		2012
	Pretax expense	$	51.4	$	64.9	$	63.4
	Tax benefit	18		22.7		22.2
	The decrease in expense for 2014 reflects adjustments recorded to our performance-based equity awards based on current estimates of the level of performance expected to be reached.
	Net Income Per Share  Basic net income per share is computed using the weighted average number of common shares outstanding during the reporting period, excluding unvested time-based and performance-based restricted equity awards that are subject to forfeiture. Diluted net income per share includes common stock equivalents assumed outstanding during the period. Our common stock equivalents include the incremental shares assumed to be issued for:
	•	earned but unvested time-based restricted equity awards, and
	•	certain unvested performance-based restricted equity awards that satisfied contingency conditions for common stock equivalents during the period.
	Supplemental Cash Flow Information  Cash includes only bank demand deposits. Non-cash activity includes declared but unpaid dividends. For the years ended December 31, we paid the following:
	(millions)	2014		2013		2012
	Income taxes	$	515	$	497	$	389.1
	Interest	116		122.3		135
New Accounting Standards In May 2014, the Financial Accounting Standards Board (FASB) issued an accounting standard update (ASU) related to the accounting for revenue from contracts with customers. This standard is intended to help reduce diversity in practice and enhance comparability between entities related to revenue recognition and is effective for fiscal years beginning after December 15, 2016 (2017 for calendar-year companies). Since the accounting for insurance contracts is outside of the scope of this ASU, we do not expect this standard to have a significant impact on our financial condition, cash flows, or results of operations.
In June 2014, the FASB issued an ASU related to the accounting for share-based payments when the terms of an employee award can be achieved after the requisite service period. To the extent an equity award contains provisions that permit an employee who leaves the company before the performance targets are reached to receive some or all of the benefits of the award if and as the award later vests, this standard requires companies to recognize the compensation cost during the employee's remaining service period. This standard is effective for fiscal years beginning after December 15, 2015 (2016 for calendar-year companies). We plan to adopt this standard prospectively.  Although this standard may require an acceleration of the expense recognition of our share-based payment awards, we do not expect it to have a significant impact on our financial condition, cash flows, or results of operations.
In June 2014, the FASB also issued an ASU related to repurchase-to-maturity transactions, repurchase financings, and related disclosures. The intent is to clarify that repurchase-to-maturity transactions must be accounted for and disclosed as secured borrowings, rather than potentially accounted for as sales, as permissible under certain circumstances in the previous guidance. This guidance is effective for annual and interim periods after December 15, 2014 (2015 for calendar-year companies). We do not typically engage in these type of transactions; therefore, we do not expect this standard to have a significant impact on our financial condition, cash flows, or results of operations.

Investments

Investments	12 Months Ended
	Dec. 31, 2014
Investments Schedule [Abstract]
Investments	INVESTMENTS
	The following tables present the composition of our investment portfolio by major security type, consistent with our internal classification of how we manage, monitor, and measure the portfolio:
	($ in millions)	Cost			Gross Unrealized Gains			Gross Unrealized Losses			Net Realized Gains (Losses)1			Fair Value			% of Total Fair Value
	31-Dec-14
	Fixed maturities:
	U.S. government obligations	$	2,641.10		$	27.3		$	(1.3	)	$	0		$	2,667.10		14	%
	State and local government obligations	2,095.70			44.6			(1.1		)	0			2,139.20			11.2
	Foreign government obligations	14.2			0			0			0			14.2			0.1
	Corporate debt securities	2,813.90			32.9			(10.4		)	0.3			2,836.70			14.9
	Residential mortgage-backed securities	1,635.50			34.5			(10.8		)	(0.7		)	1,658.50			8.7
	Commercial mortgage-backed securities	2,278.70			39.3			(2.6		)	0.2			2,315.60			12.2
	Other asset-backed securities	1,634.90			3.8			(0.8		)	0.8			1,638.70			8.6
	Redeemable preferred stocks	260.2			24.7			(5.7		)	0			279.2			1.5
	Total fixed maturities	13,374.20			207.1			(32.7		)	0.6			13,549.20			71.2
	Equity securities:
	Nonredeemable preferred stocks	590.4			201.1			(6.4		)	42.4			827.5			4.4
	Common equities	1,289.20			1,213.20			(10.1		)	0			2,492.30			13.1
	Short-term investments	2,149.00			0			0			0			2,149.00			11.3
	Total portfolio2,3	$	17,402.80		$	1,621.40		$	(49.2	)	$	43		$	19,018.00		100	%
	($ in millions)	Cost			Gross Unrealized Gains			Gross Unrealized Losses			Net Realized Gains (Losses)1			Fair Value			% of Total Fair Value
	31-Dec-13
	Fixed maturities:
	U.S. government obligations	$	3,630.40		$	48.4		$	(16.6	)	$	0		$	3,662.20		20.3	%
	State and local government obligations	2,247.30			27.1			(18.4		)	0			2,256.00			12.5
	Foreign government obligations	15.6			0			0			0			15.6			0.1
	Corporate debt securities	2,885.00			60.4			(20.4		)	1.6			2,926.60			16.2
	Residential mortgage-backed securities	1,110.10			31.9			(14.1		)	0			1,127.90			6.2
	Commercial mortgage-backed securities	2,154.40			43.9			(37.8		)	0			2,160.50			12
	Other asset-backed securities	1,073.00			6.6			(2.1		)	0.2			1,077.70			6
	Redeemable preferred stocks	299.5			24.1			(9.7		)	0			313.9			1.7
	Total fixed maturities	13,415.30			242.4			(119.1		)	1.8			13,540.40			75
	Equity securities:
	Nonredeemable preferred stocks	445.7			258.7			(4.5		)	11.3			711.2			3.9
	Common equities	1,451.10			1,081.80			(2.4		)	0			2,530.50			14
	Short-term investments	1,272.60			0			0			0			1,272.60			7.1
	Total portfolio2,3	$	16,584.70		$	1,582.90		$	(126.0	)	$	13.1		$	18,054.70		100	%
	1 Represents net holding period gains (losses) on certain hybrid securities (discussed below).
	2 Our portfolio reflects the effect of unsettled security transactions and collateral on open derivative positions; at December 31, 2014, $31.3 million was included in "other liabilities," compared to $61.3 million at December 31, 2013.
	3 The total fair value of the portfolio included $1.9 billion and $1.8 billion at December 31, 2014 and 2013, respectively, of securities held in a consolidated, non-insurance subsidiary of the holding company, net of any unsettled security transactions.
	Our short-term investments include commercial paper and other investments that are expected to mature within one year. At December 31, 2014 and 2013, we had $5.7 million and $6.3 million, respectively, in treasury bills issued by the Australian government, included in short-term investments. We did not hold any repurchase transactions where we lent collateral at December 31, 2014 or 2013. To the extent our repurchase transactions were with the same counterparty and subject to an enforceable master netting arrangement, we could elect to offset these transactions. Consistent with past practice, we have elected not to offset these transactions and therefore report these transactions on a gross basis on our balance sheets.
	Also included in short-term investments are reverse repurchase commitment transactions, where we loan cash to internally approved counterparties and receive U.S. Treasury Notes pledged as collateral against the cash borrowed. Our exposure to credit risk is limited due to the nature of the collateral (i.e., U.S. Treasury Notes) received. We have counterparty exposure on these trades in the event of a counterparty default to the extent the general collateral security's value is below the amount of cash we delivered to acquire the collateral. The short-term duration of the transactions (primarily overnight) reduces that exposure.
	We had no open reverse repurchase commitments at December 31, 2014, compared to $200.0 million with one counterparty at December 31, 2013. During 2014, our largest outstanding balance of reverse repurchase commitments was $500.0 million, which was open for one day; the average daily balance of reverse repurchase commitments was $158.8 million.
	Included in our fixed-maturity and equity securities are hybrid securities, which are reported at fair value at December 31:
	(millions)	2014				2013
	Fixed maturities:
	Corporate debt securities	$	139.8			$	164.2
	Residential mortgage-backed securities	120.7				0
	Commercial mortgage-backed securities	31.2				0
	Other asset-backed securities	13.7				14.8
	Total fixed maturities	305.4				179
	Equity securities:
	Nonredeemable preferred stocks	122.3				60.3
	Total hybrid securities	$	427.7			$	239.3
	Certain corporate debt securities are accounted for as hybrid securities since they were acquired at a substantial premium and contain a change-in-control put option (derivative) that permits the investor, at its sole option if and when a change in control is triggered, to put the security back to the issuer at a 1% premium to par. Due to this change-in-control put option and the substantial market premium paid to acquire these securities, there is the potential that the election to put, upon the change in control, would result in an acceleration of the recognition of the remaining premium paid on these securities in our results of operations. This would result in a loss of $9.3 million as of December 31, 2014, if all of these bonds experienced a simultaneous change in control and we elected to exercise all of our put options. The put feature limits the potential loss in value that could be experienced in the event a corporate action occurs that results in a change in control that materially diminishes the credit quality of the issuer. We are under no obligation to exercise the put option we hold if a change in control occurs.
	The residential mortgage-backed securities accounted for as hybrid securities are obligations of the issuer with payments of principal based on the performance of a reference pool of loans. This embedded derivative results in the securities incorporating the risk of default from both the issuer and the related loan pool.
	The commercial mortgage-backed securities in the table above contain fixed interest rate reset features that will increase the coupons in the event the securities are not fully paid off on the anticipated repayment date. These reset features have the potential to more than double our initial purchase yield for each security.
	The other asset-backed security in the table above represents one hybrid security that was acquired at a deep discount to par due to a failing auction, and contains a put option that allows the investor to put that security back to the auction at par if the auction is restored. This embedded derivative had the potential to more than double our initial investment yield at acquisition.
	The hybrid securities in our nonredeemable preferred stock portfolio are perpetual preferred stocks that have call features with fixed-rate coupons, whereby the change in value of the call features is a component of the overall change in value of the preferred stocks.
	Our securities are reported at fair value, with the changes in fair value of these securities (other than hybrid securities and derivative instruments) reported as a component of accumulated other comprehensive income, net of deferred income taxes. The changes in fair value of the hybrid securities and derivative instruments are recorded as a component of net realized gains (losses) on securities.
	At December 31, 2014, bonds and certificates of deposit in the principal amount of $153.7 million were on deposit to meet state insurance regulatory and/or rating agency requirements. We did not have any securities of any one issuer, excluding U.S. government obligations, with an aggregate cost or fair value exceeding 10% of total shareholders’ equity at December 31, 2014 or 2013. At December 31, 2014, we did not have any debt securities that were non-income producing during the preceding 12 months.
	Fixed Maturities  The composition of fixed maturities by maturity at December 31, 2014, was:
	(millions)	Cost				Fair Value
	Less than one year	$	3,180.10			$	3,217.40
	One to five years	7,026.30				7,097.20
Five to ten years	3,093.00				3,152.90
Ten years or greater	59				65.9
Total1	$	13,358.40			$	13,533.40
1 Excludes $15.8 million related to our open interest rate swap positions.
Asset-backed securities are classified in the maturity distribution table based upon their projected cash flows. All other securities which do not have a single maturity date are reported based upon expected average maturity. Contractual maturities may differ from expected maturities because the issuers of the securities may have the right to call or prepay obligations.
Gross Unrealized Losses  As of December 31, 2014, we had $39.1 million of gross unrealized losses in our fixed-income securities (i.e., fixed-maturity securities, nonredeemable preferred stocks, and short-term investments) and $10.1 million in our common equities. We currently do not intend to sell the fixed-income securities and determined that it is more likely than not that we will not be required to sell these securities for the period of time necessary to recover their cost bases. A review of our fixed-income securities indicated that the issuers were current with respect to their interest obligations and that there was no evidence of any deterioration of the current cash flow projections that would indicate we would not receive the remaining principal at maturity. For common equities, 88% of our common stock portfolio was indexed to the Russell 1000; as such, this portfolio may contain securities in a loss position for an extended period of time, subject to possible write-downs, as described below. We may retain these securities as long as the portfolio and index correlation remain similar. To the extent there is issuer-specific deterioration, we may write-down the securities of that issuer. The remaining 12% of our common stocks were part of a managed equity strategy selected and administered by external investment advisors. If our review of loss position securities indicated there was a fundamental, or market, impairment on these securities that was determined to be other-than-temporary, we would recognize a write-down in accordance with our stated policy.
The following tables show the composition of gross unrealized losses by major security type and by the length of time that individual securities have been in a continuous unrealized loss position:
	Total No. of Sec.		Total			Gross Unrealized Losses			Less than 12 Months									12 Months or Greater
			Fair
($ in millions)			Value						No. of Sec.		Fair			Unrealized Losses				No. of Sec.		Fair			Unrealized Losses
											Value									Value
31-Dec-14
Fixed maturities:
U.S. government obligations	11		$	428.2		$	(1.3	)	5		$	150.7		$	(0.3	)		6		$	277.5		$	(1.0	)
State and local government obligations	46		234.2			(1.1		)	28		177.9			(0.4		)		18		56.3			(0.7		)
Corporate debt securities	53		843.2			(10.4		)	43		647.5			(6.1		)		10		195.7			(4.3		)
Residential mortgage-backed securities	70		844.2			(10.8		)	33		465.2			(3.1		)		37		379			(7.7		)
Commercial mortgage-backed securities	63		723.4			(2.6		)	54		667.5			(1.4		)		9		55.9			(1.2		)
Other asset-backed securities	44		741.8			(0.8		)	42		715.7			(0.7		)		2		26.1			(0.1		)
Redeemable preferred stocks	3		103			(5.7		)	1		33			(1.0		)		2		70			(4.7		)
Total fixed maturities	290		3,918.00			(32.7		)	206		2,857.50			(13.0		)		84		1,060.50			(19.7		)
Equity securities:
Nonredeemable preferred stocks	8		231.4			(6.4		)	5		143.2			(3.6		)		3		88.2			(2.8		)
Common equities	20		68.4			(10.1		)	19		61.8			(9.6		)		1		6.6			(0.5		)
Total equity securities	28		299.8			(16.5		)	24		205			(13.2		)		4		94.8			(3.3		)
Total portfolio	318		$	4,217.80		$	(49.2	)	230		$	3,062.50		$	(26.2	)		88		$	1,155.30		$	(23.0	)
	Total No. of Sec.		Total			Gross			Less than 12 Months									12 Months or Greater
			Fair			Unrealized
($ in millions)			Value			Losses			No. of Sec.		Fair			Unrealized				No. of Sec.		Fair			Unrealized
											Value			Losses						Value			Losses
31-Dec-13
Fixed maturities:
U.S. government obligations	29		$	1,444.30		$	(16.6	)	28		$	1,434.60		$	(16.3	)		1		$	9.7		$	(0.3	)
State and local government obligations	141		844.2			(18.4		)	119		759.3			(17.1		)		22		84.9			(1.3		)
Corporate debt securities	51		997.6			(20.4		)	45		831.1			(17.8		)		6		166.5			(2.6		)
Residential mortgage-backed securities	66		763.5			(14.1		)	45		597.6			(7.9		)		21		165.9			(6.2		)
Commercial mortgage-backed securities	76		1,061.90			(37.8		)	60		809.2			(19.7		)		16		252.7			(18.1		)
Other asset-backed securities	25		287.2			(2.1		)	22		233.3			(1.8		)		3		53.9			(0.3		)
Redeemable preferred stocks	4		122.7			(9.7		)	0		0			0				4		122.7			(9.7		)
Total fixed maturities	392		5,521.40			(119.1		)	319		4,665.10			(80.6		)		73		856.3			(38.5		)
Equity securities:
Nonredeemable preferred stocks	7		142.3			(4.5		)	7		142.3			(4.5		)		0		0			0
Common equities	24		59.7			(2.4		)	20		58.5			(2.4		)		4		1.2			0
Total equity securities	31		202			(6.9		)	27		200.8			(6.9		)		4		1.2			0
Total portfolio	423		$	5,723.40		$	(126.0	)	346		$	4,865.90		$	(87.5	)		77		$	857.5		$	(38.5	)
During 2014, the number of securities in our fixed-maturity portfolio with unrealized losses decreased, reflecting a combination of an increase in prices associated with a general decline in interest rates at certain maturities, as well as sales of securities for portfolio management reasons. We had no material decreases in valuation as a result of credit rating downgrades on our fixed-maturity securities during the year. All of the fixed-maturity securities in an unrealized loss position at December 31, 2014 in the table above are current with respect to required principal and interest payments. Unrealized losses on our nonredeemable preferred stocks related to eight issues with unrealized losses, averaging approximately 3% of our total cost of those securities. A review of these securities concluded that the unrealized losses are market-related adjustments to the values, which were determined not to be other-than-temporary, and we continue to expect to recover our initial investments on these securities. The unrealized losses in our common stock portfolio in the less than 12 months category reflect losses that developed late in the fourth quarter 2014. A review of the securities in a loss position did not uncover fundamental issues with the issuers that would indicate other-than-temporary impairments existed. Additionally, expectations for recovery in the next 12 months would put the fair values at or above our current book values. Lastly, we determined, as of the balance sheet date, that it was not likely these securities would be sold prior to that recovery.
Other-Than-Temporary Impairment (OTTI)  The following table shows the total non-credit portion of the OTTI recorded in accumulated other comprehensive income, reflecting the original non-credit loss at the time the credit impairment was determined:
	December 31,
(millions)	2014			2013
Fixed maturities:
Residential mortgage-backed securities	$	(44.1	)	$	(44.1	)
Commercial mortgage-backed securities	(0.6		)	(0.9		)
Total fixed maturities	$	(44.7	)	$	(45.0	)
The following tables provide rollforwards of the amounts related to credit losses recognized in earnings for the periods ended December 31, 2014, 2013, and 2012, for which a portion of the OTTI losses were also recognized in accumulated other comprehensive income at the time the credit impairments were determined and recognized:
(millions)	Residential			Commercial			Total
	Mortgage-			Mortgage-
	Backed			Backed
Balance at December 31, 2013	$	19.2		$	0.4		$	19.6
Credit losses for which an OTTI was previously recognized	0			0			0
Credit losses for which an OTTI was not previously recognized	0			0			0
Reductions for securities sold/matured	(0.1		)	0			(0.1		)
Change in recoveries of future cash flows expected to be collected1,2	(6.4		)	0			(6.4		)
Reductions for previously recognized credit impairments	0			0			0
written-down to fair value3
Balance at December 31, 2014	$	12.7		$	0.4		$	13.1
(millions)	Residential			Commercial			Total
	Mortgage-			Mortgage-
	Backed			Backed
Balance at December 31, 2012	$	27.1		$	0.6		$	27.7
Credit losses for which an OTTI was previously recognized	0.1			0			0.1
Credit losses for which an OTTI was not previously recognized	0			0			0
Reductions for securities sold/matured	0			0			0
Change in recoveries of future cash flows expected to be collected1,2	(7.8		)	(0.2		)	(8.0		)
Reductions for previously recognized credit impairments	(0.2		)	0			(0.2		)
written-down to fair value3
Balance at December 31, 2013	$	19.2		$	0.4		$	19.6
(millions)	Residential			Commercial			Total
	Mortgage-			Mortgage-
	Backed			Backed
Balance at December 31, 2011	$	34.5		$	1.3		$	35.8
Credit losses for which an OTTI was previously recognized	0.1			0			0.1
Credit losses for which an OTTI was not previously recognized	0.3			0			0.3
Reductions for securities sold/matured	0			(0.2		)	(0.2		)
Change in recoveries of future cash flows expected to be collected1,2	(3.8		)	(0.2		)	(4.0		)
Reductions for previously recognized credit impairments	(4.0		)	(0.3		)	(4.3		)
written-down to fair value3
Balance at December 31, 2012	$	27.1		$	0.6		$	27.7
1 Reflects expected recovery of prior period impairments that will be accreted into income over the remaining life of the security.
2 Includes $4.3 million, $2.6 million, and $1.4 million at December 31, 2014, 2013, and 2012, respectively, recognized in income in excess of the cash flows expected to be collected at the time of the write-downs.
3 Reflects reductions of prior credit impairments where the current credit impairment requires writing securities down to fair value (i.e., no remaining non-credit loss).
Although we determined that it is more likely than not that we will not be required to sell the securities prior to the recovery of their respective cost bases (which could be maturity), we are required to measure the amount of credit losses on the securities that were determined to be other-than-temporarily impaired. In that process, we considered a number of factors and inputs related to the individual securities. The methodology and significant inputs used to measure the amount of credit losses in our portfolio included: current performance indicators on the underlying assets (e.g., delinquency rates, foreclosure rates, and default rates); credit support (via current levels of subordination); historical credit ratings; and updated cash flow expectations based upon these performance indicators. In order to determine the amount of credit loss, if any, the net present value of the cash flows expected (i.e., expected recovery value) was calculated using the current book yield for each security, and was compared to its current amortized value. In the event that the net present value was below the amortized value, a credit loss was deemed to exist, and the security was written down.
Net Realized Gains (Losses)  The components of net realized gains (losses) for the years ended December 31, were:
(millions)	2014			2013			2012
Gross realized gains on security sales
Fixed maturities:
U.S. government obligations	$	24		$	8.5		$	20.2
State and local government obligations	9.3			7.7			15
Corporate and other debt securities	37.2			47.7			58.1
Residential mortgage-backed securities	2.7			3			1.2
Commercial mortgage-backed securities	17			10			19.3
Other asset-backed securities	0			0			0.9
Redeemable preferred stocks	2.7			0			0.7
Total fixed maturities	92.9			76.9			115.4
Equity securities:
Nonredeemable preferred stocks	90			126.3			78.2
Common equities	107.3			68.6			167
Subtotal gross realized gains on security sales	290.2			271.8			360.6
Gross realized losses on security sales
Fixed maturities:
U.S. government obligations	(7.6		)	(3.7		)	(1.9		)
State and local government obligations	(0.5		)	0			0
Corporate and other debt securities	(2.8		)	(6.2		)	(0.6		)
Residential mortgage-backed securities	(0.2		)	0			0
Commercial mortgage-backed securities	(8.3		)	(1.8		)	0
Redeemable preferred stocks	(3.2		)	(0.1		)	(0.4		)
Total fixed maturities	(22.6		)	(11.8		)	(2.9		)
Equity securities:
Nonredeemable preferred stocks	0			(0.1		)	(1.1		)
Common equities	(7.3		)	(0.6		)	(27.1		)
Subtotal gross realized losses on security sales	(29.9		)	(12.5		)	(31.1		)
Net realized gains (losses) on security sales
Fixed maturities:
U.S. government obligations	16.4			4.8			18.3
State and local government obligations	8.8			7.7			15
Corporate and other debt securities	34.4			41.5			57.5
Residential mortgage-backed securities	2.5			3			1.2
Commercial mortgage-backed securities	8.7			8.2			19.3
Other asset-backed securities	0			0			0.9
Redeemable preferred stocks	(0.5		)	(0.1		)	0.3
Total fixed maturities	70.3			65.1			112.5
Equity securities:
Nonredeemable preferred stocks	90			126.2			77.1
Common equities	100			68			139.9
Subtotal net realized gains (losses) on security sales	260.3			259.3			329.5
Other-than-temporary impairment losses
Fixed maturities:
Residential mortgage-backed securities	0			(0.6		)	(1.6		)
Commercial mortgage-backed securities	0			0			(0.1		)
Total fixed maturities	0			(0.6		)	(1.7		)
Equity securities:
Common equities	(7.2		)	(5.5		)	(1.8		)
Subtotal other-than-temporary impairment losses	(7.2		)	(6.1		)	(3.5		)
Other gains (losses)
Hybrid securities	30.5			6.4			14.3
Derivative instruments	(64.1		)	56.6			(43.1		)
Litigation settlements	4.7			2.2			9.6
Subtotal other gains (losses)	(28.9		)	65.2			(19.2		)
Total net realized gains (losses) on securities	$	224.2		$	318.4		$	306.8
Gross realized gains and losses were predominantly the result of sales transactions in our fixed-income portfolio related to
movements in credit spreads and interest rates and sales from our equity-indexed portfolio. In addition, gains and losses reflect recoveries from litigation settlements and holding period valuation changes on hybrids and derivatives. Also included are write-downs for securities determined to be other-than-temporarily impaired in our fixed-maturity and/or equity portfolios.
Net Investment Income  The components of net investment income for the years ended December 31, were:
(millions)	2014			2013			2012
Fixed maturities:
U.S. government obligations	$	46.2		$	50.2		$	49.8
State and local government obligations	50.1			48			51.1
Foreign government obligations	0.4			0.2			0
Corporate debt securities	82.1			98.8			107.5
Residential mortgage-backed securities	44.9			28.1			16.1
Commercial mortgage-backed securities	66			74.8			82.2
Other asset-backed securities	16.7			16.7			20.3
Redeemable preferred stocks	15.5			21.2			24.2
Total fixed maturities	321.9			338			351.2
Equity securities:
Nonredeemable preferred stocks	38.6			36.2			43.8
Common equities	46.6			45.8			44.9
Short-term investments	1.3			2			3.1
Investment income	408.4			422			443
Investment expenses	(18.9		)	(18.8		)	(15.4		)
Net investment income	$	389.5		$	403.2		$	427.6
The decrease in our investment income during 2014 was due in part to an increase in short-term investments held and lower yields on securities purchased during the year.
Trading Securities  At December 31, 2014 and 2013, we did not hold any trading securities and we did not have any net realized gains (losses) on trading securities for the years ended December 31, 2014, 2013, and 2012.
Derivative Instruments  For all derivative positions discussed below, realized holding period gains and losses are netted with any upfront cash that may be exchanged under the contract to determine if the net position should be classified either as an asset or liability. To be reported as a net derivative asset and a component of the available-for-sale portfolio, the inception-to-date realized gain on the derivative position at period end would have to exceed any upfront cash received. On the other hand, a net derivative liability would include any inception-to-date realized loss plus the amount of upfront cash received (or netted, if upfront cash was paid) and would be reported as a component of other liabilities. These net derivative assets/liabilities are not separately disclosed on the balance sheet due to their immaterial effect on our financial condition, cash flows, and results of operations.
The following table shows the status of our derivative instruments at December 31, 2014 and 2013, and for the years ended December 31, 2014, 2013, and 2012:
(millions)											Balance Sheet2							Comprehensive
																		Income Statement
	Notional Value1											Assets						Pretax Net Realized
												(Liabilities)						Gains (Losses)
												Fair Value
																		Years ended
	December 31,											December 31,						December 31,
Derivatives	2014			2013			2012			Purpose	Classification	2014			2013			2014			2013			2012
designated as:
Hedging instruments
Closed:
Ineffective cash flow hedge	$	44		$	54		$	31		Manage	NA	$	0		$	0		$	0.5		$	0.8		$	0.6
										interest
										rate risk
Non-hedging instruments
Assets:
Interest rate swaps	750			750			0			Manage portfolio duration	Investments - fixed	15.8			68.1			(64.6		)	59.8			0
											maturities
Liabilities:
Interest rate swaps	0			0			1,263			Manage	Other liabilities	0			0			0			0			(42.7		)
										portfolio
										duration
Closed:
Interest rate swaps	0			1,263			0			Manage	NA	0			0			0			(4.0		)	0
										portfolio
										duration
Corporate credit default swaps	0			0			25			Manage	NA	0			0			0			0			(1.0		)
										credit
										risk
Total	NA			NA			NA					$	15.8		$	68.1		$	(64.1	)	$	56.6		$	(43.1	)
NA =ot Applicable
1 The amounts represent the value held at year end for open positions and the maximum amount held during the year for closed positions.
2 To the extent we hold both derivative assets and liabilities with the same counterparty that are subject to an enforceable master netting arrangement, we expect that we will report them on a gross basis on our balance sheets, consistent with our historical presentation.
CASH FLOW HEDGES
In April 2014, upon issuance of $350 million of 4.35% Senior Notes due 2044 (the “4.35% Senior Notes”), we closed a forecasted debt issuance hedge, which was entered into to hedge against a possible rise in interest rates, and recognized a $1.6 million pretax loss as part of accumulated other comprehensive income (loss); the loss will be recognized as an adjustment to interest expense and amortized over the life of the 4.35% Senior Notes.
Our ineffective cash flow hedge, which is reflected in the table above, resulted from the repurchase of a portion of our 6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067 during each of the last three years, and we reclassified the unrealized gain on forecasted transactions to net realized gains on securities.
During 2014, we recognized $2.0 million as a net decrease to interest expense on our closed debt issuance cash flow hedges, compared to $2.1 million during both 2013 and 2012.
See Note 4 – Debt for further discussion.
INTEREST RATE SWAPS
We use interest rate swap contracts primarily to manage the fixed-income portfolio duration. At December 31, 2014, 2013, and 2012, we held interest rate swap positions for which we are paying a fixed rate and receiving a variable rate, effectively shortening the duration of our fixed-income portfolio. On the open positions, since inception, interest rates have increased; however, as interest rates fell during 2014, our fair value gain decreased by $52.3 million.
During 2013, we closed three interest rate swap positions including a 9-year interest rate swap position (opened in 2009) and two 5-year interest rate swap positions (opened in 2011); in each case, we were paying a fixed rate and receiving a variable rate, effectively shortening the duration of our fixed-income portfolio.
As of December 31, 2014 and 2013, the balance of the cash collateral that we had received from the applicable counterparty on our open positions was $16.1 million and $62.7 million, respectively. As of December 31, 2012, the balance of the cash collateral that we had delivered to the applicable counterparty on the then open positions was $105.0 million.
CORPORATE CREDIT DEFAULT SWAPS
We held no credit default swaps during 2014 or 2013. During 2012, we closed one position that was opened during 2008, on a corporate issuer within the financial services sector for which we bought credit default protection in the form of a credit default swap for a 5-year time horizon. We held this protection to reduce our exposure to additional valuation declines on a preferred stock position of the same issuer.

Fair_Value

Fair Value	12 Months Ended
	Dec. 31, 2014
Fair Value Disclosures [Abstract]
Fair Value	FAIR VALUE
	We have categorized our financial instruments, based on the degree of subjectivity inherent in the method by which they are valued, into a fair value hierarchy of three levels, as follows:
	•	Level 1:  Inputs are unadjusted, quoted prices in active markets for identical instruments at the measurement date (e.g., U.S. government obligations, active exchange-traded equity securities, and certain short-term securities).
	•	Level 2:  Inputs (other than quoted prices included within Level 1) that are observable for the instrument either directly or indirectly (e.g., certain corporate and municipal bonds and certain preferred stocks). This includes: (i) quoted prices for similar instruments in active markets, (ii) quoted prices for identical or similar instruments in markets that are not active, (iii) inputs other than quoted prices that are observable for the instruments, and (iv) inputs that are derived principally from or corroborated by observable market data by correlation or other means.
	•	Level 3:  Inputs that are unobservable. Unobservable inputs reflect our subjective evaluation about the assumptions market participants would use in pricing the financial instrument (e.g., certain structured securities and privately held investments).
	Determining the fair value of the investment portfolio is the responsibility of management. As part of the responsibility, we evaluate whether a market is distressed or inactive in determining the fair value for our portfolio. We review certain market level inputs to evaluate whether sufficient activity, volume, and new issuances exist to create an active market. Based on this evaluation, we concluded that there was sufficient activity related to the sectors and securities for which we obtained valuations.
	The composition of the investment portfolio by major security type was:
		Fair Value
	(millions)	Level 1		Level 2			Level 3		Total			Cost
	31-Dec-14
	Fixed maturities:
	U.S. government obligations	$	2,667.10	$	0		$	0	$	2,667.10		$	2,641.10
	State and local government obligations	0		2,139.20			0		2,139.20			2,095.70
	Foreign government obligations	14.2		0			0		14.2			14.2
	Corporate debt securities	0		2,836.70			0		2,836.70			2,813.90
	Subtotal	2,681.30		4,975.90			0		7,657.20			7,564.90
	Asset-backed securities:
	Residential mortgage-backed	0		1,658.50			0		1,658.50			1,635.50
	Commercial mortgage-backed	0		2,304.00			11.6		2,315.60			2,278.70
	Other asset-backed	0		1,638.70			0		1,638.70			1,634.90
	Subtotal asset-backed securities	0		5,601.20			11.6		5,612.80			5,549.10
	Redeemable preferred stocks:
	Financials	0		97.9			0		97.9			77.3
	Utilities	0		65.3			0		65.3			65
	Industrials	0		116			0		116			117.9
	Subtotal redeemable preferred stocks	0		279.2			0		279.2			260.2
	Total fixed maturities	2,681.30		10,856.30			11.6		13,549.20			13,374.20
	Equity securities:
	Nonredeemable preferred stocks:
	Financials	204.1		554.1			69.3		827.5			590.4
	Utilities	0		0			0		0			0
	Subtotal nonredeemable preferred stocks	204.1		554.1			69.3		827.5			590.4
	Common equities:
	Common stocks	2,491.90		0			0		2,491.90			1,288.80
	Other risk investments	0		0			0.4		0.4			0.4
	Subtotal common equities	2,491.90		0			0.4		2,492.30			1,289.20
	Total fixed maturities and equity securities	5,377.30		11,410.40			81.3		16,869.00			15,253.80
	Short-term investments	1,937.00		212			0		2,149.00			2,149.00
	Total portfolio	$	7,314.30	$	11,622.40		$	81.3	$	19,018.00		$	17,402.80
	Debt	$	0	$	2,527.50		$	0	$	2,527.50		$	2,164.70
		Fair Value
	(millions)	Level 1		Level 2			Level 3		Total			Cost
	31-Dec-13
	Fixed maturities:
	U.S. government obligations	$	3,662.20	$	0		$	0	$	3,662.20		$	3,630.40
	State and local government obligations	0		2,256.00			0		2,256.00			2,247.30
	Foreign government obligations	15.6		0			0		15.6			15.6
	Corporate debt securities	0		2,926.60			0		2,926.60			2,885.00
	Subtotal	3,677.80		5,182.60			0		8,860.40			8,778.30
	Asset-backed securities:
	Residential mortgage-backed	0		1,127.70			0.2		1,127.90			1,110.10
	Commercial mortgage-backed	0		2,131.50			29		2,160.50			2,154.40
	Other asset-backed	0		1,077.70			0		1,077.70			1,073.00
	Subtotal asset-backed securities	0		4,336.90			29.2		4,366.10			4,337.50
	Redeemable preferred stocks:
	Financials	0		102.8			0		102.8			84.2
	Utilities	0		65.6			0		65.6			64.9
	Industrials	0		145.5			0		145.5			150.4
	Subtotal redeemable preferred stocks	0		313.9			0		313.9			299.5
	Total fixed maturities	3,677.80		9,833.40			29.2		13,540.40			13,415.30
	Equity securities:
	Nonredeemable preferred stocks:
	Financials	240.8		414.6			39		694.4			431.5
	Utilities	0		16.8			0		16.8			14.2
Subtotal nonredeemable preferred stocks	240.8		431.4			39		711.2			445.7
Common equities:
Common stocks	2,530.00		0			0		2,530.00			1,450.60
Other risk investments	0		0			0.5		0.5			0.5
Subtotal common equities	2,530.00		0			0.5		2,530.50			1,451.10
Total fixed maturities and equity securities	6,448.60		10,264.80			68.7		16,782.10			15,312.10
Short-term investments	987.8		284.8			0		1,272.60			1,272.60
Total portfolio	$	7,436.40	$	10,549.60		$	68.7	$	18,054.70		$	16,584.70
Debt	$	0	$	2,073.70		$	0	$	2,073.70		$	1,860.90
Our portfolio valuations classified as either Level 1 or Level 2 in the above tables are priced exclusively by external sources, including: pricing vendors, dealers/market makers, and exchange-quoted prices. During 2014, we had two nonredeemable preferred stocks with a value of $41.7 million that were transferred from Level 2 to Level 1 due to the availability of a consistent exchange price. During 2013, we did not have any securities that were transferred between Level 1 and Level 2. We recognize transfers between levels at the end of the reporting period.
Our short-term security holdings classified as Level 1 are highly liquid, actively marketed, and have a very short duration, primarily 30 days or less to redemption. These securities are held at their original cost, adjusted for any accretion of discount, since that value very closely approximates what an active market participant would be willing to pay for such securities. The remainder of our short-term securities are classified as Level 2 and are not priced externally since these securities continually trade at par value. These securities are classified as Level 2 since they are primarily longer-dated auction securities issued by municipalities that contain a redemption put feature back to the auction pool with a redemption period typically less than seven days. The auction pool is created by a liquidity provider and if the auction is not available at the end of the seven days, we have the right to put the security back to the issuer at par.
At December 31, 2014, vendor-quoted prices represented 50% of our Level 1 classifications (excluding short-term investments), compared to 56% at December 31, 2013. The securities quoted by vendors in Level 1 primarily represent our holdings in U.S. Treasury Notes, which are frequently traded and the quotes are considered similar to exchange-traded quotes. The balance of our Level 1 pricing comes from quotes obtained directly from trades made on active exchanges. The year-over-year decline in vendor-quoted Level 1 prices was due to a reduction of U.S. Treasury Notes with the funds deployed primarily to short-term investments.
At December 31, 2014, vendor-quoted prices comprised 97% of our Level 2 classifications (excluding short-term investments), while dealer-quoted prices represented 3%, compared to 98% and 2% at December 31, 2013, respectively. In our process for selecting a source (e.g., dealer, pricing service) to provide pricing for securities in our portfolio, we reviewed documentation from the sources that detailed the pricing techniques and methodologies used by these sources and determined if their policies adequately considered market activity, either based on specific transactions for the particular security type or based on modeling of securities with similar credit quality, duration, yield, and structure that were recently transacted. Once a source is chosen, we continue to monitor any changes or modifications to their processes by reviewing their documentation on internal controls for pricing and market reviews. We review quality control measures of our sources as they become available to determine if any significant changes have occurred from period to period that might indicate issues or concerns regarding their evaluation or market coverage.
As part of our pricing procedures, we obtain quotes from more than one source to help us fully evaluate the market price of securities. However, our internal pricing policy is to use a consistent source for individual securities in order to maintain the integrity of our valuation process. Quotes obtained from the sources are not considered binding offers to transact. Under our policy, when a review of the valuation received from our selected source appears to be outside of what is considered market level activity (which is defined as trading at spreads or yields significantly different than those of comparable securities or outside the general sector level movement without a reasonable explanation), we may use an alternate source’s price. To the extent we determine that it may be prudent to substitute one source’s price for another, we will contact the initial source to obtain an understanding of the factors that may be contributing to the significant price variance, which often leads the source to adjust their pricing input data for future pricing.
To allow us to determine if our initial source is providing a price that is outside of a reasonable range, we review our portfolio pricing on a weekly basis. We frequently challenge prices from our sources when a price provided does not match our expectations based on our evaluation of market trends and activity. Initially, we perform a review of our portfolio by sector to identify securities whose prices appear outside of a reasonable range. We then perform a more detailed review of fair values for securities disclosed as Level 2. We review dealer bids and quotes for these and/or similar securities to determine the market level context for our valuations. We then evaluate inputs relevant for each class of securities disclosed in the preceding hierarchy tables.
For our structured debt securities, including commercial, residential, and asset-backed securities, we evaluate available market-related data for these and similar securities related to collateral, delinquencies, and defaults for historical trends and reasonably estimable projections, as well as historical prepayment rates and current prepayment assumptions and cash flow estimates. We further stratify each class of our structured debt securities into more finite sectors (e.g., planned amortization class, first pay, second pay, senior, subordinated, etc.) and use duration, credit quality, and coupon to determine the appropriate fair value.
For our corporate debt and preferred stock (redeemable and nonredeemable) portfolios, we review securities by duration, coupon, and credit quality, as well as changes in interest rate and credit spread movements within that stratification. The review also includes recent trades, including: volume traded at various levels that establish a market, issuer specific fundamentals, and industry specific economic news as it comes to light.
For our municipal securities (e.g., general obligations, revenue, and housing), we stratify the portfolio to evaluate securities by type, coupon, credit quality, and duration to review price changes relative to credit spread and interest rate changes. Additionally, we look to economic data as it relates to geographic location as an indication of price-to-call or maturity predictors. For municipal housing securities, we look to changes in cash flow projections, both historical and reasonably estimable projections, to understand yield changes and their effect on valuation.
Lastly, for our short-term securities, we look at acquisition price relative to the coupon or yield. Since our short-term securities are typically 90 days or less to maturity, with the majority listed in Level 2 being seven days or less to redemption, acquisition price is the best estimate of fair value.
We also review data assumptions as supplied by our sources to determine if that data is relevant to current market conditions. In addition, we independently review each sector for transaction volumes, new issuances, and changes in spreads, as well as the overall movement of interest rates along the yield curve to determine if sufficient activity and liquidity exists to provide a credible source for our market valuations.
During each valuation period, we create internal estimations of portfolio valuation (performance returns), based on current market-related activity (i.e., interest rate and credit spread movements and other credit-related factors) within each major sector of our portfolio. We compare our internally generated portfolio results with those generated based on quotes we received externally and research material valuation differences. We compare our results to index returns for each major sector adjusting for duration and credit quality differences to better understand our portfolio’s results. Additionally, we review on a monthly basis our external sales transactions and compare the actual final market sales price to a previous market valuation price. This review provides us further validation that our pricing sources are providing market level prices, since we are able to explain significant price changes (i.e., greater than 2%) as known events occur in the marketplace and affect a particular security’s price at sale.
This analysis provides us with additional comfort regarding the source’s process, the quality of its review, and its willingness to improve its analysis based on feedback from clients. We believe this effort helps ensure that we are reporting the most representative fair values for our securities.
Except as described below, our Level 3 securities are also priced externally; however, due to several factors (e.g., nature of the securities, level of activity, and lack of similar securities trading to obtain observable market level inputs), these valuations are more subjective in nature. Certain private equity investments and fixed-income investments included in the Level 3 category are valued using external pricing supplemented by internal review and analysis.
After all the valuations are received and our review is complete, if the inputs used by vendors are determined to not contain sufficient observable market information, we will reclassify the affected security valuations to Level 3. At December 31, 2014 and 2013, securities in our fixed-maturity portfolio listed as Level 3 were comprised substantially of securities that were either: (i) private placement deals, (ii) thinly held and/or traded securities, or (iii) non-investment-grade securities with little liquidity. Based on these factors, it was difficult to independently verify observable market inputs that were used to generate the external valuations we received. Despite the lack of sufficient observable market information for our Level 3 securities, we believe the valuations received in conjunction with our procedures for evaluating third-party prices support the fair values reported in the financial statements.
At December 31, 2014, we had one private preferred equity security (in ARX Holding Corp.) with a value of $69.3 million that was priced internally. The same security had a value of $39.0 million at December 31, 2013. The increase in value is due to a higher price to book ratio multiple included in the terms of the stock purchase agreement we entered into during December 2014 to purchase a majority interest in ARX Holding Corp. This was the only internally-priced security in the portfolio at December 31, 2014 and 2013.
We review the prices from our external sources for reasonableness using internally developed assumptions to derive prices for the securities, which are then compared to the prices we received. Based on our review, all the prices received from external sources remain unadjusted.
The following tables provide a summary of changes in fair value associated with Level 3 assets for the years ended December 31, 2014 and 2013:
	Level 3 Fair Value
(millions)	Fair Value at Dec. 31, 2013		Calls/			Purchases		Sales			Net Realized			Change in			Net			Fair Value at Dec. 31, 2014
			Maturities/								(Gain)/Loss			Valuation			Transfers
			Paydowns								on Sales						In (Out)1
Fixed maturities:
Asset-backed securities:
Residential mortgage-backed	$	0.2	$	0		$	0	$	(0.1	)	$	0.1		$	(0.2	)	$	0		$	0
Commercial mortgage-backed	29		(3.6		)	0		0			0			(0.2		)	(13.6		)	11.6
Total fixed maturities	29.2		(3.6		)	0		(0.1		)	0.1			(0.4		)	(13.6		)	11.6
Equity securities:
Nonredeemable preferred stocks:
Financials2	39		0			0		0			0			30.3			0			69.3
Common equities:
Other risk investments	0.5		(0.1		)	0		0			0			0			0			0.4
Total Level 3 securities	$	68.7	$	(3.7	)	$	0	$	(0.1	)	$	0.1		$	29.9		$	(13.6	)	$	81.3
1 The $13.6 million was transferred out of Level 3 and into Level 2 due to an improvement in the security's underlying collateral and an increase in liquidity and market activity in comparable securities.
2 The $30.3 million represents a net holding period gain on our investment in ARX Holding Corp., which is reflected in net realized gains (losses) on securities in the comprehensive income statement.
	Level 3 Fair Value
(millions)	Fair Value at Dec. 31, 2012		Calls/			Purchases		Sales			Net Realized			Change in			Net			Fair Value at Dec. 31, 2013
			Maturities/								(Gain)/Loss			Valuation			Transfers
			Paydowns								on Sales						In (Out)1
Fixed maturities:
Asset-backed securities:
Residential mortgage-backed	$	45.5	$	(28.6	)	$	125.1	$	0		$	0		$	(0.4	)	$	(141.4	)	$	0.2
Commercial mortgage-backed	25.3		(3.4		)	0		0			0			7.1			0			29
Total fixed maturities	70.8		(32.0		)	125.1		0			0			6.7			(141.4		)	29.2
Equity securities:
Nonredeemable preferred stocks:
Financials2	31.9		0			0		0			0			7.1			0			39
Common equities:
Other risk investments	12		(0.5		)	0.3		(2.4		)	(36.0		)	27.1			0			0.5
Total Level 3 securities	$	114.7	$	(32.5	)	$	125.4	$	(2.4	)	$	(36.0	)	$	40.9		$	(141.4	)	$	68.7
1 The $141.4 million was transferred out of Level 3 and into Level 2 due to an increase in liquidity and trading volume in the market.
2 The $7.1 million represents a net holding period gain on our investment in ARX Holding Corp., which is reflected in net realized gains (losses) on securities in the comprehensive income statement.
The following table provides a summary of the quantitative information about Level 3 fair value measurements for our applicable securities at December 31:
	Quantitative Information about Level 3 Fair Value Measurements
($ in millions)	Fair Value at Dec. 31, 2014		Valuation Technique	Unobservable Input	Unobservable Input Assumption
Fixed maturities:
Asset-backed securities:
Residential mortgage-backed	$	0	NA	NA	NA
Commercial mortgage-backed	11.6		External vendor	Prepayment rate1	0
Total fixed maturities	11.6
Equity securities:
Nonredeemable preferred stocks:
Financials	69.3		Multiple of tangible net book value	Price to book ratio multiple	2.6
Subtotal Level 3 securities	80.9
Third-party pricing exemption securities2	0.4
Total Level 3 securities	$	81.3
NA=ot Applicable since we did not hold any residential mortgage-backed Level 3 securities at December 31, 2014.
1 Assumes that one security has 0% of the principal amount of the underlying loans that will be paid off prematurely in each year.
2 The fair values for these securities were obtained from non-binding external sources where unobservable inputs are not reasonably available to us.
	Quantitative Information about Level 3 Fair Value Measurements
($ in millions)	Fair Value at Dec. 31, 2013		Valuation Technique	Unobservable Input	Unobservable Input Assumption
Fixed maturities:
Asset-backed securities:
Residential mortgage-backed	$	0.2	External vendor	Prepayment rate1	0
Commercial mortgage-backed	29		External vendor	Prepayment rate2	0
Total fixed maturities	29.2
Equity securities:
Nonredeemable preferred stocks:
Financials	39		Multiple of tangible net book value	Price to book ratio multiple	1.9
Subtotal Level 3 securities	68.2
Third-party pricing exemption securities3	0.5
Total Level 3 securities	$	68.7
1 Assumes that one security has 0% of the principal amount of the underlying loans that will be paid off prematurely in each year.
2 Assumes that two securities have 0% of the principal amount of the underlying loans that will be paid off prematurely in each year.
3 The fair values for these securities were obtained from non-binding external sources where unobservable inputs are not reasonably available to us.
Due to the relative size of the securities’ fair values compared to the total portfolio’s fair value, any changes in pricing methodology would not have a significant change in valuation that would materially impact net and comprehensive income. During the years ended December 31, 2014 and 2013, there were no material assets or liabilities measured at fair value on a nonrecurring basis.

Debt

Debt	12 Months Ended
	Dec. 31, 2014
Debt Disclosure [Abstract]
Debt	DEBT
	Debt at December 31 consisted of:
		2014						2013
	(millions)	Carrying			Fair			Carrying		Fair
		Value			Value			Value		Value
	3.75% Senior Notes due 2021 (issued: $500.0, August 2011)	$	497.8		$	535.6		$	497.6	$	509.1
	6 5/8% Senior Notes due 2029 (issued: $300.0, March 1999)	295.5			400.6			295.3		359.6
	6.25% Senior Notes due 2032 (issued: $400.0, November 2002)	394.8			527.9			394.6		473.7
	4.35% Senior Notes due 2044 (issued: $350.0, April 2014)	346.3			378.9			0		0
	6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067 (issued: $1,000.0, June 2007; outstanding: $632.8 and $677.1)	630.3			684.5			673.4		731.3
	Total	$	2,164.70		$	2,527.50		$	1,860.90	$	2,073.70
	All of the outstanding debt was issued by The Progressive Corporation. Debt includes amounts we have borrowed and contributed to the capital of our insurance subsidiaries or used, or have available for use, for other business purposes. Fair values are obtained from external sources. There are no restrictive financial covenants or credit rating triggers on our debt.
	Interest on all debt is payable semiannually at the stated rates. However, the 6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067 (the “6.70% Debentures”) will only bear interest at this fixed annual rate through, but excluding, June 15, 2017. Thereafter, the 6.70% Debentures will bear interest at an annual rate equal to the three-month LIBOR plus 2.0175%, and interest will be payable quarterly until the 6.70% Debentures are redeemed or retired.
	Except for the 6.70% Debentures, all principal is due at the maturity stated in the table above. The 6.70% Debentures will become due on June 15, 2037, the scheduled maturity date, but only to the extent that we have received sufficient net proceeds from the sale of certain qualifying capital securities. We must use our commercially reasonable efforts, subject to certain market disruption events, to sell enough qualifying capital securities to permit repayment of the 6.70% Debentures in full on the scheduled maturity date or, if sufficient proceeds are not realized from the sale of such qualifying capital securities by such date, on each interest payment date thereafter. Any remaining outstanding principal will be due on June 15, 2067, the final maturity date.
	In April 2014, we issued $350 million of 4.35% Senior Notes due 2044 (the “4.35% Senior Notes”).  We received proceeds of $346.3 million, after deducting underwriter’s discounts and commissions. In addition, we incurred expenses of approximately $0.7 million related to the issuance.  Upon issuance of the 4.35% Senior Notes, we closed a forecasted debt issuance hedge, which was entered into to hedge against a possible rise in interest rates, and recognized a $1.6 million pretax loss as part of accumulated other comprehensive income (loss); the loss will be recognized as an adjustment to interest expense and amortized over the life of the 4.35% Senior Notes.
	We retired the entire $150 million of our 7% Notes at maturity in October 2013. The 3.75% Senior Notes, the 6 5/8% Senior Notes, the 6.25% Senior Notes, and the 4.35% Senior Notes (collectively, “Senior Notes”) may be redeemed in whole or in part at any time, at our option, subject to a “make-whole” provision. The 6.70% Debentures may be redeemed, in whole or in part, at any time: (a) prior to June 15, 2017, at a redemption price equal to the greater of (i) 100% of the principal amount of the 6.70% Debentures being redeemed, or (ii) a “make-whole” amount, in each case plus any accrued and unpaid interest; or (b) on or after June 15, 2017, at a redemption price equal to 100% of the principal amount of the 6.70% Debentures being redeemed, plus any accrued and unpaid interest.
	During 2014 and 2013, we repurchased, in the open market, $44.3 million and $54.1 million, respectively, in aggregate principal amount of our 6.70% Debentures. Since the amount paid exceeded the carrying value of the debt we repurchased, we recognized losses on these extinguishments of $4.8 million and $4.3 million for 2014 and 2013, respectively.
	Prior to issuance of each of the Senior Notes and 6.70% Debentures, we entered into forecasted debt issuance hedges against possible rises in interest rates. Upon issuance of the applicable debt securities, the hedges were closed and we recognized unrealized gains (losses) as part of accumulated other comprehensive income. The original unrealized gain (loss) at the time of each debt issuance and the unamortized balance at December 31, 2014, on a pretax basis, of these hedges, were as follows:
	(millions)	Unrealized Gain (Loss)			Unamortized Balance
		at Debt Issuance			at December 31, 2014
	3.75% Senior Notes	$	(5.1	)	$	(3.6	)
	6 5/8% Senior Notes	(4.2		)	(3.2		)
	6.25% Senior Notes	5.1			4
	4.35% Senior Notes	(1.6		)	(1.6		)
	6.70% Debentures	34.4			6.6
	The gains (losses) on these hedges are deferred and are being amortized as adjustments to interest expense over the life of the related Senior Notes, and over the 10-year fixed interest rate term for the 6.70% Debentures. In addition to this amortization, during 2014 and 2013, we reclassified $0.5 million and $0.8 million, respectively, on a pretax basis, from accumulated other comprehensive income on the balance sheet to net realized gains on securities on the comprehensive income statement, reflecting the portion of the unrealized gain on forecasted transactions that was related to the portion of the 6.70% Debentures repurchased during the periods.
	In March 2014, we renewed the unsecured, discretionary line of credit (the "Line of Credit") with PNC Bank, National Association (PNC) in the maximum principal amount of $100 million. The prior line of credit, entered into in March 2013, has expired. The Line of Credit is on substantially the same terms and conditions as the prior line of credit. Subject to the terms and conditions of the Line of Credit documents, advances under the Line of Credit (if any) will bear interest at a variable rate equal to the higher of PNC's Prime Rate or the sum of the Federal Funds Open Rate plus 50 basis points. Each advance must be repaid on the 30th day after the advance or, if earlier, on March 25, 2015, the expiration date of the Line of Credit. Prepayments are permitted without penalty. All advances under the Line of Credit are subject to PNC's discretion. We had no borrowings under the Line of Credit or the prior line of credit in 2014 or 2013.
	Aggregate required principal payments on debt outstanding are as follows:
	(millions)
	Year	Payments
	2015	$	0
	2016	0
	2017	0
	2018	0
	2019	0
	Thereafter	2,182.80
	Total	$	2,182.80

Income_Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Income Taxes	INCOME TAXES
	The components of our income tax provision were as follows:
	(millions)	2014			2013			2012
	Current tax provision	$	594.4		$	460.2		$	424.8
	Deferred tax expense (benefit)	32			94.4			(9.4		)
	Total income tax provision	$	626.4		$	554.6		$	415.4
	The provision for income taxes in the accompanying consolidated statements of comprehensive income differed from the statutory rate as follows:
	($ in millions)	2014						2013					2012
	Income before income taxes	$	1,907.40					$	1,720.00				$	1,317.70
	Tax at statutory rate	$	667.6		35	%		$	602		35	%	$	461.2		35	%
	Tax effect of:
	Dividends received deduction	(18.3		)	(1	)		(17.6		)	(1	)	(18.2		)	(1	)
	Exempt interest income	(13.8		)	(1	)		(13.1		)	(1	)	(14.7		)	(1	)
	Tax-deductible dividends	(6.5		)	0			(13.6		)	(1	)	(11.9		)	(1	)
	Tax credits	(2.2		)	0			(2.3		)	0		0			0
	Other items, net	(0.4		)	0			(0.8		)	0		(1.0		)	0
	Total income tax provision	$	626.4		33	%		$	554.6		32	%	$	415.4		32	%
	Deferred income taxes reflect the effect for financial statement reporting purposes of temporary differences between the financial statement carrying amounts and the tax bases of assets and liabilities. At December 31, 2014 and 2013, the components of the net deferred tax asset (liability) were as follows:
	(millions)	2014			2013
	Deferred tax assets:
	Unearned premiums reserve	$	378.8		$	361
	Investment basis differences	60.6			94.8
	Non-deductible accruals	208			200.7
	Loss and loss adjustment expense reserves	76.9			92
	Other	7.5			14.7
	Deferred tax liabilities:
	Net unrealized gains on securities	(550.3		)	(509.9		)
	Hedges on forecasted transactions	(0.8		)	(2.2		)
	Deferred acquisition costs	(160.0		)	(156.7		)
	Property and equipment	(100.9		)	(99.6		)
	Prepaid expenses	(11.4		)	(14.4		)
	Deferred gain on extinguishment of debt	(3.0		)	(4.8		)
	Other	(4.3		)	(4.0		)
	Net deferred tax liability	$	(98.9	)	$	(28.4	)
	Although realization of the deferred tax assets is not assured, management believes that it is more likely than not that the deferred tax assets will be realized based on our expectation that we will be able to fully utilize the deductions that are ultimately recognized for tax purposes and, therefore, no valuation allowance was needed at December 31, 2014 or 2013.
	At December 31, 2014, we had $49.4 million of net taxes payable (included in other liabilities on the balance sheet), compared to net taxes recoverable of $17.1 million at December 31, 2013 (included in other assets on the balance sheet).
	We have been a participant in the Compliance Assurance Program (CAP) since 2007. Under CAP, the Internal Revenue Service (IRS) begins its examination process for the tax year before the tax return is filed, by examining significant transactions and events as they occur. The goal of the CAP program is to expedite the exam process and to reduce the level of uncertainty regarding a taxpayer’s tax filing positions.
	All federal income tax years prior to 2011 are closed. The IRS exams for 2011-2013 have been completed; therefore, we consider these years to be effectively settled.
	We recognize interest and penalties, if any, related to unrecognized tax benefits as a component of income tax expense. We have not recorded any unrecognized tax benefits, or any related interest and penalties, as of December 31, 2014 and 2013. For the year ended December 31, 2013, $0.2 million of interest benefit has been recorded in the tax provision. For the years ended December 31, 2014 and 2012, no interest expense or benefit has been recorded in the tax provision.

Loss_And_Loss_Adjustment_Expen

Loss And Loss Adjustment Expense Reserves	12 Months Ended
	Dec. 31, 2014
Loss and Loss Adjustment Expense Reserves Disclosures [Abstract]
Loss And Loss Adjustment Expense Reserves	LOSS AND LOSS ADJUSTMENT EXPENSE RESERVES
	Activity in the loss and loss adjustment expense reserves is summarized as follows:
	(millions)	2014			2013		2012
	Balance at January 1	$	8,479.70		$	7,838.40	$	7,245.80
	Less reinsurance recoverables on unpaid losses	1,045.90			862.1		785.7
	Net balance at January 1	7,433.80			6,976.30		6,460.10
	Incurred related to:
	Current year	13,330.30			12,427.30		11,926.00
	Prior years	(24.1		)	45.1		22
	Total incurred	13,306.20			12,472.40		11,948.00
	Paid related to:
	Current year	8,831.50			8,095.00		7,895.30
	Prior years	4,237.00			3,919.90		3,536.50
	Total paid	13,068.50			12,014.90		11,431.80
	Net balance at December 31	7,671.50			7,433.80		6,976.30
	Plus reinsurance recoverables on unpaid losses	1,185.90			1,045.90		862.1
	Balance at December 31	$	8,857.40		$	8,479.70	$	7,838.40
	We experienced favorable reserve development of $24.1 million in 2014, compared to unfavorable reserve development of $45.1 million and $22.0 million in 2013 and 2012, respectively, which is reflected as “Incurred related to prior years” in the table above.
	2014
	•The favorable prior year reserve development was primarily attributable to accident year 2010.
	•	Favorable reserve development in our Commercial Lines business was partially offset by unfavorable development in our Agency auto business. Our Direct auto business experienced slightly favorable development.
	•	The favorable reserve development in our Commercial Lines business was primarily related to favorable case reserve development on our high limit policies.
	•	In Agency auto, the unfavorable development was primarily attributable to personal injury protection (PIP)loss reserves and to the adjusting and other loss adjustment expense reserves.
	2013
	•	Approximately 80% of the unfavorable reserve development was attributable to accident year 2011, while the remaining 20% was related to accident year 2012. The aggregate reserve development for accident years 2010 and prior was slightly favorable.
	•	About 55% of our unfavorable reserve development was in our Commercial Lines business, with the remainder split about equally between our Personal Lines business and our run-off businesses. In our Personal Lines business, unfavorable development in our Agency auto channel was offset in large part by favorable development in our Direct auto channel.
	•	The unfavorable reserve development in our Agency auto business was in our IBNR reserves due to higher frequency and severity on late emerging claims, as primarily reflected in the “all other development.”
	•	Lower than anticipated severity costs on case reserves were the primary contributor to the favorable development in our Direct auto business.
	•	In our Commercial Lines business, we experienced unfavorable development due to higher frequency and severity on late emerging claims primarily in our bodily injury coverage for our truck business.
	•	In our other businesses, we experienced unfavorable development primarily due to reserve increases in our run-off professional liability group business based on internal actuarial reviews of our claims history.
	2012
	•	The unfavorable prior year reserve development was primarily attributable to accident year 2011 and, to a lesser extent, accident year 2010. The aggregate reserve development for accident years 2009 and prior was favorable. Despite overall unfavorable reserve development, we did experience favorable reserve adjustments, primarily in our loss adjustment expenses and our personal auto bodily injury reserves for accident years 2009 and 2008.
	•	Slightly more than half of the total unfavorable reserve development was attributable to our Commercial Lines business, with the remainder in our personal auto business. In our personal auto business, unfavorable development in the Agency channel was partially offset by favorable development in the Direct channel, primarily reflecting that unfavorable development on our PIP coverage was more skewed to the Agency channel, and that our Direct business had favorable development on our collision coverage, as we experienced more subrogation recoveries in this channel.
	•	Our personal auto product’s development was primarily attributable to unfavorable development in our Florida PIP coverage and an increase in our estimate of bodily injury severity for accident year 2011.
	•	Unfavorable development in our Commercial Lines business reflects higher than anticipated frequency and severity costs on late emerging claims and higher settlements on large losses.
	Because we are primarily an insurer of motor vehicles, we have limited exposure to environmental, asbestos, and general liability claims. We have established reserves for such exposures, in amounts that we believe to be adequate based on information currently known. These claims are not expected to have a material effect on our liquidity, financial condition, cash flows, or results of operations.
	We write personal and commercial auto insurance throughout the United States and could be exposed to hurricanes or other catastrophes. Although the occurrence of a major catastrophe could have a significant effect on our monthly or quarterly results, we believe that, based on historical experience, such an event would not be so material as to disrupt the overall normal operations of Progressive. We are unable to predict the frequency or severity of any such events that may occur in the near term or thereafter.

Reinsurance

Reinsurance	12 Months Ended
	Dec. 31, 2014
Reinsurance Disclosures [Abstract]
Reinsurance	REINSURANCE
	The effect of reinsurance on premiums written and earned for the years ended December 31, was as follows:
		2014							2013							2012
	(millions)	Written			Earned				Written			Earned				Written			Earned
	Direct premiums	$	18,914.80		$	18,648.40			$	17,562.80		$	17,317.90			$	16,558.80		$	16,207.60
	Ceded	(260.2		)	(249.9		)		(223.1		)	(214.5		)		(186.1		)	(189.6		)
	Net premiums	$	18,654.60		$	18,398.50			$	17,339.70		$	17,103.40			$	16,372.70		$	16,018.00
	Our ceded premiums consist of “State Plans” and “Non-State Plans.” State Plans include: (i) amounts ceded to state-provided reinsurance facilities, including the Michigan Catastrophic Claims Association (MCCA) and the North Carolina Reinsurance Facility (NCRF), and (ii) state-mandated involuntary Commercial Auto Insurance Procedures/Plans (CAIP). Collectively, the State Plans accounted for 97%, 97%, and 98% of our ceded premiums for the years ended December 31, 2014, 2013, and 2012, respectively; the MCCA and NCRF together accounted for 75%, 77%, and 80% of the ceded premiums for these same time periods.
	Losses and loss adjustment expenses were net of reinsurance ceded of $322.7 million in 2014, $347.0 million in 2013, and $230.7 million in 2012.
	Our prepaid reinsurance premiums and reinsurance recoverables were comprised of the following at December 31:
		Prepaid Reinsurance Premiums												Reinsurance Recoverables
	($ in millions)	2014						2013						2014						2013
	MCCA	$	32.8		38	%		$	29.5		40	%		$	1,018.80		83	%		$	875.9	80	%
	CAIP	26.5			31			21.1			28			110.1			9			79.3		7
	NCRF	21.9			26			20.5			27			51.1			4			50.1		5
	State Plans	81.2			95			71.1			95			1,180.00			96			1,005.30		92
	Non-State Plans	4.1			5			3.8			5			51.9			4			84.9		8
	Total	$	85.3		100	%		$	74.9		100	%		$	1,231.90		100	%		$	1,090.20	100	%
	Reinsurance contracts do not relieve us from our obligations to policyholders. Failure of reinsurers to honor their obligations could result in losses to Progressive. Since substantially all of our reinsurance is through State Plans, our exposure to losses from their failure is minimal, since the plans are funded by mechanisms supported by the insurance companies in the state. We evaluate the financial condition of our other reinsurers and monitor concentrations of credit risk to minimize our exposure to significant losses from reinsurer insolvencies.

Statutory_Financial_Informatio

Statutory Financial Information	12 Months Ended
	Dec. 31, 2014
Statutory Financial Information Disclosures [Abstract]
Statutory Financial Information	STATUTORY FINANCIAL INFORMATION
	Consolidated statutory surplus was $6,442.8 million and $5,991.0 million at December 31, 2014 and 2013, respectively. Statutory net income was $1,289.5 million, $1,086.3 million, and $808.3 million for the years ended December 31, 2014, 2013, and 2012, respectively.
	At December 31, 2014, $549.2 million of consolidated statutory surplus represented net admitted assets of our insurance subsidiaries and affiliate that are required to meet minimum statutory surplus requirements in such entities’ states of domicile. The companies may be licensed in states other than their states of domicile, which may have higher minimum statutory surplus requirements. Generally, the net admitted assets of insurance companies that, subject to other applicable insurance laws and regulations, are available for transfer to the parent company cannot include the net admitted assets required to meet the minimum statutory surplus requirements of the states where the companies are licensed.
	During 2014, the insurance subsidiaries paid aggregate cash dividends of $1,000.2 million to the parent company. Based on the dividend laws currently in effect, the insurance subsidiaries could pay aggregate dividends of $1,346.5 million in 2015 without prior approval from regulatory authorities, provided the dividend payments are not made within 12 months of previous dividends paid by the applicable subsidiary.

Employee_Benefit_Plans

Employee Benefit Plans	12 Months Ended
	Dec. 31, 2014
Employee Benefit Plans Disclosures [Abstract]
Employee Benefit Plans	EMPLOYEE BENEFIT PLANS
	Retirement Plans  Progressive has a defined contribution pension plan (401(k) Plan) that covers most employees who are United States residents and have been employed with the company for at least 30 days. Under this plan, Progressive matches up to a maximum of 6% of an employee’s eligible compensation contributed to the plan. Employee and company matching contributions are invested, at the direction of the employee, in a number of investment options available under the plan, including various mutual funds, a self-directed brokerage option, and a Progressive common stock fund. The Progressive common stock fund is an employee stock ownership program (ESOP) within the 401(k) Plan. At December 31, 2014, the ESOP held 26.2 million of our common shares, all of which are included in shares outstanding. Dividends on these shares are reinvested in common shares or paid out in cash at the election of the participant and the related tax benefit is recorded as part of our tax provision.
	Matching contributions made by the company for the 401(k) Plan were $74.8 million, $69.9 million, and $66.5 million for the years ended December 31, 2014, 2013, and 2012, respectively.
	Postemployment Benefits  Progressive provides various postemployment benefits to former or inactive employees who meet eligibility requirements, and to their beneficiaries and covered dependents. Postemployment benefits include salary continuation and disability-related benefits, including workers’ compensation and, if elected, continuation of health-care benefits for specified limited periods. The liability for these benefits was $22.5 million and $24.0 million at December 31, 2014 and 2013, respectively.
	Postretirement Benefits  We provide postretirement health and life insurance benefits to all employees who met requirements as to age and length of service at December 31, 1988. There are approximately 115 people who are eligible for these postretirement benefits. Our funding policy for these benefits is to contribute annually, to a 501(c)(9) trust, the maximum amount that can be deducted for federal income tax purposes.
	Incentive Compensation Plans – Employees  Our incentive compensation programs include both non-equity incentive plans (cash) and equity incentive plans. Cash incentive compensation includes a cash bonus program for a limited number of senior executives and our Gainsharing program for other employees; the structures of these programs are similar in nature. Equity incentive compensation plans provide for the granting of restricted stock awards and restricted stock unit awards (collectively, “restricted equity awards”) to key members of management. The amounts charged to income for the incentive compensation plans for the years ended December 31, were:
		2014						2013							2012
	(millions)	Pretax			After Tax			Pretax			After Tax				Pretax		After Tax
	Cash	$	266.2		$	173		$	234.5		$	152.4			$	207	$	134.6
	Equity	51.4			33.4			64.9			42.2				63.4		41.2
	Our 2003 Incentive Plan has expired, and no new awards may be made under this plan; however, awards granted prior to the plan’s expiration remain outstanding. Our 2010 Equity Incentive Plan, which provides for the granting of equity-based compensation to officers and other key employees, originally authorized 18.0 million shares.
	We have issued restricted equity awards since 2003. In March 2010, we began issuing restricted stock units in lieu of restricted stock as the form of our equity awards. The restricted equity awards are issued as either time-based or performance-based awards. The time-based awards vest in equal installments upon the lapse of specified periods of time, typically three, four, and five years. All restricted stock units are settled at or after vesting in Progressive common shares from existing treasury shares on a one-to-one basis.
	The performance-based awards were granted to our Chief Executive Officer as his sole equity award in each of the last five years, and to approximately 45 other executives and senior managers in addition to their time-based awards, to provide additional incentive to achieve pre-established profitability and growth targets. Vesting of these awards is contingent upon the achievement of predetermined performance goals within specified time periods. The targets for the performance-based awards, as well as the number of units that ultimately may vest, vary by grant. All performance-based awards include a specified number of shares or units that will be issued if performance meets a specified target. For awards granted in 2013 and 2014, performance-based awards based on insurance operating results may vest between 0% to 250% of target depending on the results achieved. The performance-based awards based on insurance operating results granted in 2010 through 2012, and all performance awards based on investment results, may vest from 0% to 200% of the target amount depending on the results achieved. Outstanding performance-based awards made prior to March 2009 will either vest or be forfeited in full (i.e., no partial vesting), and if performance goals are not achieved within the contractual term, the awards will expire. For awards granted prior to 2009, the maximum contractual term is ten years from the grant date, and for awards granted in or after 2009, the maximum contractual term is 5 years from the date of grant.
	Generally, time-based and performance-based equity awards are expensed pro rata over their respective vesting periods based on the market value of the awards at the time of grant. Performance-based equity awards that contain variable vesting criteria are expensed based on management’s expectation of the percentage of the award, if any, that will ultimately vest. These estimates can change periodically throughout the measurement period.
	A summary of all employee restricted equity award activity during the years ended December 31, follows:
		2014					2013						2012
	Restricted Equity Awards	Number of Shares1		Weighted			Number of		Weighted				Number of		Weighted
				Average			Shares1		Average				Shares1		Average
				Grant					Grant						Grant
				Date Fair					Date Fair						Date Fair
				Value					Value						Value
	Beginning of year	9,918,575		$	20.13		11,625,981		$	17.8			12,296,847		$	16.86
	Add (deduct):
	Granted2	3,542,984		19.32			2,738,809		22.73				2,680,229		19.11
	Vested	(4,228,673	)	16.99			(4,293,605	)	15.54				(3,188,111	)	15.23
	Forfeited	(181,322	)	20.75			(152,610	)	18.28				(162,984	)	17.93
	End of year3,4	9,051,564		$	21.27		9,918,575		$	20.13			11,625,981		$	17.8
	1 Includes both restricted stock units and restricted stock. Upon vesting, all units will be converted on a one-for-one basis into Progressive common shares funded from existing treasury shares. All performance-based awards are included at their target amounts.
	2 In 2010, we began reinvesting dividend equivalents on restricted stock units. For 2014, 2013, and 2012, the number of units "granted" shown in the table above includes 538,749, 161,077, and 440,029 of dividend equivalent units, respectively, at a weighted average grant date fair value of $0, since the dividends were factored into the grant date fair value of the original grant.
	3 At December 31, 2014, the number of shares included 2,647,530 performance-based awards at their target amounts. We expect 2,208,731 of these performance-based awards to vest, based upon our current estimate of the likelihood of achieving these pre-determined performance goals.
	4 At December 31, 2014, the total unrecognized compensation cost related to unvested equity awards was $70.5 million, which includes performance-based awards at their currently estimated vesting value. This compensation expense will be recognized into the income statement over the weighted average vesting period of 2.3 years.
	The aggregate fair value of the restricted equity awards that vested during the years ended December 31, 2014, 2013, and 2012, was $100.9 million, $91.8 million, and $57.7 million, respectively, based on the actual stock price on the vesting date. In 2014 and 2013, 340,949 and 272,617, respectively, of dividend equivalent units vested with no intrinsic value. In 2012, we also had 246,200 deferred liability awards vest with no intrinsic value since these awards were expensed based on the current market value at the end of each reporting period.
	Incentive Compensation Plans – Directors  Our 2003 Directors Equity Incentive Plan, which provides for the granting of equity-based awards, including restricted stock awards, to non-employee directors of Progressive, originally authorized 1.4 million shares.
	We currently grant restricted stock awards to our non-employee directors as their sole compensation for serving as members of the Board of Directors. The restricted stock awards are issued as time-based awards. The vesting period (i.e., requisite service period) must be a minimum of six months and one day. The time-based awards granted to date have typically included vesting periods of 11 months from the date of each grant. To the extent a director is newly appointed during the year, or a director's committee assignments change, the vesting period may be shorter, but always at least equal to six months, one day per the plan’s specifications. The restricted stock awards are expensed pro rata over their respective vesting periods based on the market value of the awards at the time of grant.
	A summary of all directors’ restricted stock activity during the years ended December 31, follows:
		2014					2013						2012
	Restricted Stock	Number of		Weighted			Number of		Weighted				Number of		Weighted
		Shares		Average			Shares		Average				Shares		Average
				Grant					Grant						Grant
				Date Fair					Date Fair						Date Fair
				Value					Value						Value
	Beginning of year	93,254		$	26.19		92,957		$	21.41			94,106		$	21.8
	Add (deduct):
	Granted	90,649		25.44			93,254		26.19				92,957		21.41
	Vested	(93,254	)	26.19			(92,957	)	21.41				(94,106	)	21.8
	Forfeited	(9,070	)	25.36			0		0				0		0
	End of year	81,579		$	25.45		93,254		$	26.19			92,957		$	21.41
	Prior to 2003, we granted nonqualified stock options as the equity component of the directors’ compensation. These options became exercisable at various dates not earlier than six months, and remain exercisable for up to ten years from the date of grant. All options granted had an exercise price equal to the market value of the common shares on the date of grant and, under the then applicable accounting guidance, no compensation expense was recorded. All option exercises were settled in Progressive common shares from existing treasury shares. All remaining 36,237 options outstanding under the 1998 Directors' Stock Option Plan were exercised during the year ended December 31, 2012.
	The total pretax intrinsic value of options exercised, and the fair value of the restricted stock vested, during the years ended December 31, 2014, 2013, and 2012, was $2.2 million, $2.3 million, and $2.5 million, respectively, based on the actual stock price at time of exercise/vesting.
	Deferred Compensation  We maintain The Progressive Corporation Executive Deferred Compensation Plan (Deferral Plan) that permits eligible executives to defer receipt of some or all of their annual bonuses and all of their annual equity awards. Deferred cash compensation is deemed invested in one or more investment funds, including common shares of Progressive, offered under the Deferral Plan and elected by the participant. All Deferral Plan distributions attributable to deferred cash compensation will be paid in cash.
	For all equity awards granted in or after March 2005, and deferred pursuant to the Deferral Plan, the deferred amounts are deemed invested in our common shares and are ineligible for transfer to other investment funds in the Deferral Plan; distributions of these deferred awards will be made in our common shares. For all restricted stock awards granted prior to that date, the deferred amounts are eligible to be transferred to any of the investment funds in the Deferral Plan; distributions of these deferred awards will be made in cash. We reserved 11.1 million of our common shares for issuance under the Deferral Plan. An irrevocable grantor trust has been established to provide a source of funds to assist us in meeting our liabilities under the Deferral Plan.
	The Deferral Plan Irrevocable Grantor Trust account held the following assets at December 31:
	(millions)	2014			2013
	Progressive common shares1	$	83.2		$	57.1
	Other investment funds2	123.9			113.1
	Total	$	207.1		$	170.2
	1 Includes 3.6 million and 2.5 million common shares as of December 31, 2014 and 2013, respectively, to be distributed in common shares.
	2 Amount is included in other assets on the balance sheet.

Segment_Information

Segment Information	12 Months Ended
	Dec. 31, 2014
Segment Reporting [Abstract]
Segment Information	SEGMENT INFORMATION
	We write personal auto and other specialty property-casualty insurance and provide related services throughout the United States. Our Personal Lines segment writes insurance for personal autos and recreational vehicles. The Personal Lines segment is comprised of both the Agency and Direct businesses. The Agency business includes business written by our network of more than 35,000 independent insurance agencies, including brokerages in New York and California, and strategic alliance business relationships (other insurance companies, financial institutions, and national agencies). The Direct business includes business written directly by us online, by phone, or on mobile devices. We also sell personal auto physical damage and property damage liability insurance via the Internet in Australia. For the years ended December 31, 2014, 2013, and 2012, net premiums earned on our Australian business were $17.1 million, $13.0 million, and $7.1 million, respectively.
	Our Commercial Lines segment writes primary liability and physical damage insurance for automobiles and trucks owned and/or operated predominantly by small businesses in the business auto, for-hire transportation, contractor, for-hire specialty, tow, and for-hire livery markets. This segment is distributed through both the independent agency and direct channels.
	Our other indemnity businesses manage our run-off businesses, including the run-off of our professional liability insurance for community banks, which was sold in 2010.
	Our service businesses provide insurance-related services, including processing CAIP business and serving as an agent for homeowners, general liability, and workers’ compensation insurance through our programs with unaffiliated insurance companies.
	All segment revenues are generated from external customers and we do not have a reliance on any major customer.
	We evaluate profitability based on pretax underwriting profit (loss) for the Personal Lines and Commercial Lines segments and for the other indemnity businesses. Pretax underwriting profit (loss) is calculated as net premiums earned plus fees and other revenues, less: (i) losses and loss adjustment expenses; (ii) policy acquisition costs; and (iii) other underwriting expenses. Service business pretax profit (loss) is the difference between service business revenues and service business expenses.
	Expense allocations are based on certain assumptions and estimates primarily related to revenue and volume; stated segment operating results would change if different methods were applied. We do not allocate assets or income taxes to operating segments. In addition, we do not separately identify depreciation and amortization expense by segment, and such allocation would be impractical. Companywide depreciation expense was $97.1 million in 2014, $101.3 million in 2013, and $94.4 million in 2012. The accounting policies of the operating segments are the same as those described in Note 1 - Reporting and Accounting Policies.
	Following are the operating results for the years ended December 31:
		2014							2013						2012
	(millions)	Revenues			Pretax				Revenues			Pretax			Revenues			Pretax
					Profit							Profit						Profit
					(Loss)							(Loss)						(Loss)
	Personal Lines
	Agency	$	9,087.00		$	683			$	8,601.50		$	542.9		$	8,103.90		$	338.9
	Direct	7,474.00			423.4				6,740.10			473.9			6,264.20			289.5
	Total Personal Lines1	16,561.00			1,106.40				15,341.60			1,016.80			14,368.10			628.4
	Commercial Lines	1,837.50			315.8				1,761.60			114.1			1,649.00			86.3
	Other indemnity	0			(11.9		)		0.2			(10.8		)	0.9			(5.8		)
	Total underwriting operations	18,398.50			1,410.30				17,103.40			1,120.10			16,018.00			708.9
	Fees and other revenues2	309.1			NA				291.8			NA			281.8			NA
	Service businesses	56			5.1				39.6			0.8			36.1			0
	Investments3	632.6			613.7				740.4			721.6			749.8			734.4
	Gains (losses) on extinguishment of debt	(4.8		)	(4.8		)		(4.3		)	(4.3		)	(1.8		)	(1.8		)
	Interest expense	NA			(116.9		)		NA			(118.2		)	NA			(123.8		)
	Consolidated total	$	19,391.40		$	1,907.40			$	18,170.90		$	1,720.00		$	17,083.90		$	1,317.70
	NA =ot Applicable
	1 Personal auto insurance accounted for 92% of the total Personal Lines segment net premiums earned in 2014, compared to 91% in 2013 and 2012; insurance for our special lines products (e.g., motorcycles, ATVs, RVs, mobile homes, watercraft, and snowmobiles) accounted for the balance of the Personal Lines net premiums earned.
	2 Pretax profit (loss) for fees and other revenues are allocated to operating segments.
	3 Revenues represent recurring investment income and total net realized gains (losses) on securities; pretax profit is net of investment expenses.
	Progressive’s management uses underwriting margin and combined ratio as primary measures of underwriting profitability. Underwriting profitability is calculated by subtracting losses and loss adjustment expenses, policy acquisition costs, and other underwriting expenses from the total of net premiums earned and fees and other revenues. The underwriting margin is the pretax underwriting profit (loss) expressed as a percentage of net premiums earned (i.e., revenues from underwriting operations). Combined ratio is the complement of the underwriting margin. Following are the underwriting margins/combined ratios for our underwriting operations for the years ended December 31:
		2014				2013				2012
		Underwriting		Combined		Underwriting		Combined		Underwriting		Combined
		Margin		Ratio		Margin		Ratio		Margin		Ratio
	Personal Lines
	Agency	7.5	%	92.5		6.3	%	93.7		4.2	%	95.8
	Direct	5.7		94.3		7		93		4.6		95.4
	Total Personal Lines	6.7		93.3		6.6		93.4		4.4		95.6
	Commercial Lines	17.2		82.8		6.5		93.5		5.2		94.8
	Other indemnity1	NM		NM		NM		NM		NM		NM
	Total underwriting operations	7.7		92.3		6.5		93.5		4.4		95.6
	1 Underwriting margins/combined ratios are not meaningful (NM) for our other indemnity businesses due to the low level of premiums earned by, and the variability of loss costs in, such businesses.

Other_Comprehensive_Income_Los

Other Comprehensive Income (Loss)	12 Months Ended
	Dec. 31, 2014
Equity [Abstract]
Other Comprehensive Income (Loss)	OTHER COMPREHENSIVE INCOME (LOSS)
	The components of other comprehensive income (loss) for the years ended December 31, were as follows:
											Components of Changes in
											Accumulated Other
											Comprehensive Income (after tax)
	(millions)	Pretax total			Total tax			After tax total			Total net			Net			Foreign
		accumulated			(provision)			accumulated			unrealized			unrealized			currency
		other			benefit			other			gains (losses)			gains on			translation
		comprehensive						comprehensive			on securities			forecasted			adjustment
		income						income						transactions
	Balance at December 31, 2013	$	1,464.10		$	(512.4	)	$	951.7		$	947		$	4.1		$	0.6
	Other comprehensive income (loss) before reclassifications:
	Investment securities	362.1			(126.7		)	235.4			235.4			0			0
	Net non-credit related OTTI losses, adjusted for valuation changes	0			0			0			0			0			0
	Forecasted transactions	(1.6		)	0.6			(1.0		)	0			(1.0		)	0
	Foreign currency translation adjustment	(1.3		)	0.4			(0.9		)	0			0			(0.9		)
	Total other comprehensive income (loss) before reclassifications	359.2			(125.7		)	233.5			235.4			(1.0		)	(0.9		)
	Less: Reclassification adjustment for amounts realized in net income by income statement line item:
	Net impairment losses recognized in earnings	(7.7		)	2.7			(5.0		)	(5.0		)	0			0
	Net realized gains (losses) on securities	255			(89.2		)	165.8			165.5			0.3			0
	Interest expense	2			(0.7		)	1.3			0			1.3			0
	Total reclassification adjustment for amounts realized in net income	249.3			(87.2		)	162.1			160.5			1.6			0
	Total other comprehensive income (loss)	109.9			(38.5		)	71.4			74.9			(2.6		)	(0.9		)
	Balance at December 31, 2014	$	1,574.00		$	(550.9	)	$	1,023.10		$	1,021.90		$	1.5		$	(0.3	)
											Components of Changes in
											Accumulated Other
											Comprehensive Income (after tax)
	(millions)	Pretax total			Total tax			After tax total			Total net			Net			Foreign
		accumulated			(provision)			accumulated			unrealized			unrealized			currency
		other			benefit			other			gains (losses)			gains on			translation
		comprehensive						comprehensive			on securities			forecasted			adjustment
		income						income						transactions
	Balance at December 31, 2012	$	1,340.00		$	(469.0	)	$	871		$	862.7		$	6.1		$	2.2
	Other comprehensive income (loss) before reclassifications:
	Investment securities	368.2			(128.9		)	239.3			239.3			0			0
	Net non-credit related OTTI losses, adjusted for valuation changes	0.4			(0.1		)	0.3			0.3			0			0
	Forecasted transactions	0			0			0			0			0			0
	Foreign currency translation adjustment	(2.5		)	0.9			(1.6		)	0			0			(1.6		)
	Total other comprehensive income (loss) before reclassifications	366.1			(128.1		)	238			239.6			0			(1.6		)
	Less: Reclassification adjustment for amounts realized in net income by income statement line item:
	Net impairment losses recognized in earnings	(5.7		)	2			(3.7		)	(3.7		)	0			0
	Net realized gains (losses) on securities	245.5			(86.0		)	159.5			159			0.5			0
	Interest expense	2.2			(0.7		)	1.5			0			1.5			0
	Total reclassification adjustment for amounts realized in net income	242			(84.7		)	157.3			155.3			2			0
	Total other comprehensive income (loss)	124.1			(43.4		)	80.7			84.3			(2.0		)	(1.6		)
	Balance at December 31, 2013	$	1,464.10		$	(512.4	)	$	951.7		$	947		$	4.1		$	0.6
											Components of Changes in
											Accumulated Other
											Comprehensive Income (after tax)
	(millions)	Pretax total			Total tax			After tax total			Total net			Net			Foreign
		accumulated			(provision)			accumulated			unrealized			unrealized			currency
		other			benefit			other			gains (losses)			gains on			translation
		comprehensive						comprehensive			on securities			forecasted			adjustment
		income						income						transactions
	Balance at December 31, 2011	$	1,065.40		$	(372.9	)	$	692.5		$	682.8		$	7.9		$	1.8
	Other comprehensive income (loss) before reclassifications:
	Investment securities	488			(170.8		)	317.2			317.2			0			0
	Net non-credit related OTTI losses, adjusted for valuation changes	7.9			(2.8		)	5.1			5.1			0			0
	Forecasted transactions	0			0			0			0			0			0
	Foreign currency translation adjustment	0.6			(0.2		)	0.4			0			0			0.4
	Total other comprehensive income (loss) before reclassifications	496.5			(173.8		)	322.7			322.3			0			0.4
	Less: Reclassification adjustment for amounts realized in net income by income statement line item:
	Net impairment losses recognized in earnings	(0.4		)	0.1			(0.3		)	(0.3		)	0			0
	Net realized gains (losses) on securities	220.1			(77.0		)	143.1			142.7			0.4			0
Interest expense	2.2			(0.8		)	1.4			0			1.4			0
Total reclassification adjustment for amounts realized in net income	221.9			(77.7		)	144.2			142.4			1.8			0
Total other comprehensive income (loss)	274.6			(96.1		)	178.5			179.9			(1.8		)	0.4
Balance at December 31, 2012	$	1,340.00		$	(469.0	)	$	871		$	862.7		$	6.1		$	2.2
In an effort to manage interest rate risk, we entered into forecasted transactions on each of our outstanding debt issuances. Upon issuing the debt, the gains (losses) recognized on these cash flow hedges are recorded as unrealized gains (losses) in accumulated other comprehensive income and amortized into interest expense over the term of the related debt issuance. We expect to reclassify $2.0 million (pretax) into income during the next 12 months, related to net unrealized gains on forecasted transactions.
To the extent we repurchased any of our outstanding debt, a portion of the unrealized gain (loss) would need to be recognized as a realized gain (loss) since the cash flow hedge is deemed ineffective. During 2014, 2013, and 2012, we repurchased in the open market a portion of our 6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067 and reclassified $0.5 million, $0.8 million, $0.6 million, respectively, on a pretax basis, from accumulated other comprehensive income on the balance sheet to net realized gains on securities on the comprehensive income statement (see Note 4 - Debt for further discussion).

Litigation

Litigation	12 Months Ended
	Dec. 31, 2014
Litigation Disclosures [Abstract]
Litigation	LITIGATION
	The Progressive Corporation and/or its insurance subsidiaries are named as defendants in various lawsuits arising out of claims made under insurance policies written by our insurance subsidiaries in the ordinary course of business. We consider all legal actions relating to such claims in establishing our loss and loss adjustment expense reserves.
	In addition, The Progressive Corporation and/or its insurance subsidiaries are named as defendants in a number of class action or individual lawsuits arising out of the operations of the insurance subsidiaries. Other insurance companies face many of these same issues. The lawsuits discussed below are in various stages of development. We plan to contest these suits vigorously, but may pursue settlement negotiations in some cases, if appropriate. The outcomes of pending cases are uncertain at this time.
	We establish accruals for lawsuits when it is probable that a loss has been or will be incurred and we can reasonably estimate its potential exposure, which may include a range of loss (referred to as a loss that is both “probable and estimable” in the discussion below). As to lawsuits in which the loss is not considered both probable and estimable, or is considered probable but not estimable, we do not establish an accrual in accordance with current accounting guidance. It is generally not possible to determine the exposure associated with our lawsuits for a number of reasons, including, without limitation, one or more of the following: liability appears to be remote; putative class action lawsuits generally pose immaterial exposure until a class is actually certified, which, historically, has not been granted by the courts in the vast majority of our cases in which certification has been sought; class definitions are often indefinite and preclude detailed exposure analysis; and complaints rarely state an amount sought as relief, and when such amount is stated, it is often a function of pleading requirements and may be unrelated to the potential exposure. The following is a discussion of potentially significant pending cases at December 31, 2014, and certain cases resolved during the three-year period then ended.
	As to the pending cases, although their outcomes are uncertain, in each case we do not believe that the outcome will have a material impact on our consolidated financial condition, cash flows, or results of operations. In addition, we do not consider the losses from the pending cases to be both probable and estimable (except as noted below), and we are unable to estimate a range of loss, if any, at this time, due to the factors discussed above. In the event that any one or more of these cases results in a substantial judgment against, or settlement by, Progressive, or if our accruals (if any) prove to be inadequate, the resulting liability could have a material effect on our consolidated financial condition, cash flows, and/or results of operations.
	Pending cases at December 31, 2014 that challenge certain of our insurance subsidiaries' practices, include:
	•	One putative class action lawsuit alleging that Progressive’s website did not adequately disclose sufficient information concerning the PIP deductibles when customers indicated they are covered by private health insurance.
	•	One putative class action lawsuit challenging the labor rates our insurance subsidiaries pay to auto body repair shops.
	•	One patent matter alleging that Progressive infringes on patented marketing technology.
	•	Two putative class action lawsuits alleging that Progressive steers customers to Service Centers and network shops to have their vehicles repaired.
	•	Four putative class action lawsuits challenging Progressive’s practice in Florida of adjusting PIP and first-party medical payments.
	•	Three putative class action lawsuits challenging our adjustment of medical bills submitted by insureds in bodily injury claims.
	•	One putative class action lawsuit challenging our policy form with regard to rejecting uninsured motorist coverage. We have established an accrual for this matter because it is probable that a loss has been incurred on this lawsuit and we were able to estimate a loss. The case is ongoing and a settlement has not been reached. The range of possible loss and amount of the accrual are not material to our consolidated financial condition, cash flows, or results of operations.
	•	One putative class action lawsuit challenging the manner in which Progressive grants a discount for anti-theft devices.
	•	Two putative class action lawsuits alleging that Progressive charged insureds for illusory uninsured motorist/underinsured motorist coverage.
	•	One putative and one certified class action lawsuit alleging that Progressive undervalues total loss claims through the use of certain valuation tools.
	•	Two conditionally certified collective class action lawsuits challenging our exempt employee classification for certain claims employees under applicable wage and hour laws.
	•	One putative class action lawsuit alleging Progressive fails to timely review and pay diminished value claims.
	•	Two qui tam lawsuits alleging Progressive does not comply with its purported obligation to reimburse Medicare for medical payments made to Medicare beneficiaries.
	•	Eighteen individual and one putative class action lawsuit pending as multi-district litigation alleging Progressive and other insurers conspire to suppress body repair shop labor rates.
	For cases that have settled, but for which settlement is not complete, an accrual has been established at our best estimate of the exposure. Settlements that are complete are fully reflected in our financial statements. The amounts accrued or paid for these settlements were not material to our consolidated financial condition, cash flows, or results of operations.
	Cases settled during 2014 include:
	•	One putative class action lawsuit alleging that Progressive steers customers to Service Centers and network shops to have their vehicles repaired. This matter was settled on an individual basis.
	•	One putative class action lawsuit alleging that Progressive negligently designed, manufactured, and deceptively advertised Snapshot® in that it purportedly drains a vehicle's battery to the point that the battery is non-functional or diminished in value. This matter was settled on an individual basis.
	•	One putative class action lawsuit alleging that Progressive violated the Telephone Consumer Protection Act in making cell phone calls to insureds. This matter was settled on an individual basis.
	Cases settled during 2013 include:
	•	One putative class action lawsuit alleging that Progressive did not reimburse any of its insureds who incurred legal fees to recover money from another Progressive insured. This case was accrued for, settled, and paid in 2013.
	•	One putative class action lawsuit alleging that Progressive improperly applies a preferred provider discount to medical payment claims. This case was accrued for and settled in 2013.
	•	One putative class action lawsuit challenging the manner in which Progressive charges premium and assesses total loss claims for commercial vehicle stated amount policies. This case was accrued for, settled, and paid in 2013.
	•	Two putative class action lawsuits challenging Progressive’s practice in Florida of adjusting PIP and first-party medical payments. Both cases were settled on an individual basis.
	Cases settled during 2012 include:
	•	One putative class action lawsuit that challenged Progressive’s use of certain automated database vendors or software to assist in the adjustment of bodily injury claims where the plaintiffs alleged that these databases or software systematically undervalued the claims; an accrual was established during 2012, and the case was paid in 2013.

Commitments_and_Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	COMMITMENTS AND CONTINGENCIES
	We have certain noncancelable operating lease commitments with lease terms greater than one year for property and computer equipment. The minimum commitments under these agreements at December 31, 2014, were as follows:
	(millions)	Commitments
	2015	$	46.2
	2016	43.7
	2017	37.2
	2018	27.1
	2019	16.4
	Thereafter	4.4
	Total	$	175
	Some of the leases have options to renew at the end of the lease periods. The expense we incurred for the leases disclosed above, as well as other operating leases that may be cancelable or have terms less than one year, was:
	(millions)	Expense
	2014	$	63.4
	2013	64.6
	2012	71.9
	We also have certain noncancelable purchase obligations. The minimum commitment under these agreements at December 31, 2014, was $493.5 million.
	As of December 31, 2014, we had no open investment funding commitments; we had no uncollateralized lines or letters of credit as of December 31, 2014 or 2013.

Dividends

Dividends	12 Months Ended
	Dec. 31, 2014
Dividends [Abstract]
Dividends	DIVIDENDS
	We maintain a policy of paying an annual variable dividend that, if declared, would be payable shortly after the close of the year. This annual variable dividend is based on a target percentage of after-tax underwriting income multiplied by a companywide performance factor (Gainshare factor), subject to the limitations discussed below. The target percentage is determined by our Board of Directors on an annual basis and announced to shareholders and the public. In December 2013, the Board determined the target percentage for 2014 to be 33-1/3% of annual after-tax underwriting income, which is unchanged from the target percentage in both 2013 and 2012.
	The Gainshare factor can range from zero to two and is determined by comparing our operating performance for the year to certain predetermined profitability and growth objectives approved by the Compensation Committee of the Board. This Gainshare factor is also used in the annual cash bonus program currently in place for our employees (our “Gainsharing program”). Although recalibrated every year, the structure of the Gainsharing program generally remains the same. For 2014, the Gainshare factor was 1.32, compared to 1.21 in 2013 and 1.12 in 2012.
	Our annual dividend program will result in a variable payment to shareholders each year, subject to certain limitations. If the Gainshare factor is zero or if our comprehensive income is less than after-tax underwriting income, no dividend would be payable under our annual variable dividend policy. In addition, the ultimate decision on whether or not a dividend will be paid is in the discretion of the Board of Directors. The Board could decide to alter our policy, or not to pay the annual variable dividend, at any time prior to the declaration of the dividend for the year. Such an action by the Board could result from, among other reasons, changes in the insurance marketplace, changes in our performance or capital needs, changes in federal income tax laws, disruptions of national or international capital markets, or other events affecting our business, liquidity, or financial position.
	Following is a summary of our shareholder dividends, both variable and special, that were paid in the last three years:
	(millions, except per share amounts)			Amount
	Dividend Type	Declared	Paid	Per		Total1
				Share
	Annual – Variable	Dec-14	Feb-15	$	0.6862	$	404.1
	Annual – Variable	Dec-13	Feb-14	0.4929		293.9
	Special	Dec-13	Feb-14	1		596.3
	Annual – Variable	Dec-12	Feb-13	0.2845		172
	Special	Oct-12	Nov-12	1		604.7
	1 Based on shares outstanding as of the record date.

Subsequent_Event

Subsequent Event	12 Months Ended
	Dec. 31, 2014
Subsequent Events [Abstract]
Subsequent Events [Text Block]	SUBSEQUENT EVENT
	On January 26, 2015, we issued $400.0 million of our 3.70% Senior Notes due 2045 (the “3.70% Senior Notes”).  We received proceeds of $394.9 million, after deducting underwriter’s discounts and commissions. In addition, we incurred expenses of approximately $0.8 million related to the issuance.  Upon issuance of the 3.70% Senior Notes, we also closed a forecasted debt issuance hedge, which was entered into to hedge against a possible rise in interest rates, and recognized a $12.9 million pretax loss as part of accumulated other comprehensive income (loss); the loss will be recognized as an adjustment to interest expense and amortized over the life of the 3.70% Senior Notes.

Reporting_And_Accounting_Polic1

Reporting And Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Nature of Operations	Nature of Operations  The Progressive Corporation, an insurance holding company formed in 1965, had 53 subsidiaries, one mutual insurance company affiliate, and one limited partnership investment affiliate (collectively the “subsidiaries”) as of December 31, 2014. Our insurance subsidiaries and mutual company affiliate (collectively the Progressive Group of Insurance Companies) provide personal and commercial automobile insurance and other specialty property-casualty insurance and related services. Our Personal Lines segment writes insurance for personal autos and recreational vehicles through both an independent insurance agency channel and a direct channel. Our Commercial Lines segment writes primary liability and physical damage insurance for automobiles and trucks owned and/or operated predominantly by small businesses through both the independent agency and direct channels. We operate our businesses throughout the United States; we also sell personal auto physical damage and property damage liability insurance via the Internet in Australia.
Consolidation Policy	Basis of Consolidation and Reporting  The accompanying consolidated financial statements include the accounts of The Progressive Corporation, its wholly owned subsidiaries, and its affiliates, in which we have a controlling financial interest. All intercompany accounts and transactions are eliminated in consolidation.
Estimates And Assumptions Policy	Estimates  We are required to make estimates and assumptions when preparing our financial statements and accompanying notes in conformity with accounting principles generally accepted in the United States of America (GAAP). As estimates develop into fact (e.g., losses are paid), results may, and will likely, differ from those estimates.
Investment Policy	Investments  Our fixed-maturity securities, equity securities, and short-term investments are accounted for on an available-for-sale basis. See Note 2 – Investments for details regarding the composition of our investment portfolio.
	Fixed-maturity securities include debt securities and redeemable preferred stocks, which may have fixed or variable principal payment schedules, may be held for indefinite periods of time, and may be used as a part of our asset/liability strategy or sold in response to changes in interest rates, anticipated prepayments, risk/reward characteristics, liquidity needs, or other economic factors. These securities are carried at fair value with the corresponding unrealized gains (losses), net of deferred income taxes, reported in accumulated other comprehensive income. Fair values are obtained from recognized pricing services or are quoted by market makers and dealers, with limited exceptions discussed in Note 3 – Fair Value.
	Included in the fixed-maturity portfolio are asset-backed securities. The asset-backed securities are generally accounted for under the retrospective method. The retrospective method recalculates yield assumptions (based on changes in interest rates or cash flow expectations) historically to the inception of the investment holding period, and applies the required adjustment, if any, to the cost basis, with the offset recorded to investment income. The prospective method is used primarily for interest-only securities, non-investment-grade asset-backed securities, and certain asset-backed securities with sub-prime loan exposure or where there is a greater risk of non-performance and where it is possible the initial investment may not be substantially recovered. The prospective method requires a calculation of expected future repayments and resets the yield to allow for future period adjustments; no current period impact to investment income or the security’s cost is made based on the cash flow update. Prepayment assumptions are based on market expectations and are updated quarterly.
	Equity securities include common stocks, nonredeemable preferred stocks, and other risk investments, and are reported at fair values. Changes in fair value of these securities, net of deferred income taxes, are reflected as unrealized gains (losses) in accumulated other comprehensive income. To the extent we hold any foreign equities or foreign currency hedges, any change in value due to exchange rate fluctuations would be limited by foreign currency hedges, if any, and would be recognized in income in the current period.
	Short-term investments may include Eurodollar deposits, commercial paper, repurchase transactions, and other securities expected to mature within one year. In addition, short-term investments can include auction rate securities (i.e., certain municipal bonds and preferred stocks). Due to the nature of auction rate securities, these securities are classified as short-term based upon their expected auction date (generally 7-49 days) rather than on their contractual maturity date (which is greater than one year at original issuance). In the event that an auction fails, the security may need to be reclassified from short-term. Changes in fair value of these securities, net of deferred income taxes, are reflected as unrealized gains (losses) in accumulated other comprehensive income.
	Trading securities are securities bought principally for the purpose of sale in the near term. To the extent we have trading securities, changes in fair value would be recognized in income in the current period. Derivative instruments, which may be used for trading purposes or classified as trading derivatives due to the characteristics of the transaction, are discussed below.
	Derivative instruments may include futures, options, forward positions, foreign currency forwards, interest rate swap agreements, and credit default swaps and may be used in the portfolio for general investment purposes or to hedge the exposure to:
	•	Changes in fair value of an asset or liability (fair value hedge),
	•	Foreign currency of an investment in a foreign operation (foreign currency hedge), or
	•	Variable cash flows of a forecasted transaction (cash flow hedge).
	To the extent we have derivatives held for general investment purposes, these derivative instruments are recognized as either assets or liabilities and measured at fair value, with changes in fair value recognized in income as a component of net realized gains (losses) on securities during the period of change.
	Derivatives designated as hedges are required to be evaluated on established criteria to determine the effectiveness of their correlation to, and ability to reduce the designated risk of, specific securities or transactions. Effectiveness is required to be reassessed regularly. Hedges that are deemed to be effective would be accounted for as follows:
	•	Fair value hedge:  changes in fair value of the hedge, as well as the hedged item, would be recognized in income in the period of change while the hedge is in effect.
	•	Foreign currency hedge:  changes in fair value of the hedge, as well as the hedged item, would be reflected as a change in translation adjustment as part of accumulated other comprehensive income. Gains and losses on the foreign currency hedge would offset the foreign exchange gains and losses on the foreign investment as they are recognized into income.
	•	Cash flow hedge:  changes in fair value of the hedge would be reported as a component of accumulated other comprehensive income and subsequently amortized into earnings over the life of the hedged transaction.
	If a hedge is deemed to become ineffective or discontinued, the following accounting treatment would be applied:
	•	Fair value hedge:  the derivative instrument would continue to be adjusted through income, while the adjustment in the change in value of the hedged item would be reflected as a change in unrealized gains (losses) as part of accumulated other comprehensive income.
	•	Foreign currency hedge:  changes in the value of the hedged item would continue to be reflected as a change in translation adjustment as part of accumulated other comprehensive income, but the derivative instrument would be adjusted through income for the current period.
	•	Cash flow hedge:  changes in fair value of the derivative instrument would be reported in income for the current period.
	For all derivative positions, net cash requirements are limited to changes in fair values, which may vary resulting from changes in interest rates, currency exchange rates, and other factors. Exposure to credit risk is limited to the carrying value; collateral may be required to limit credit risk. We have elected not to offset fair value amounts that arise from derivative positions with the same counterparty under a master netting arrangement.
	Investment securities are exposed to various risks such as interest rate, market, credit, and liquidity risk. Fair values of securities fluctuate based on the nature and magnitude of changing market conditions; significant changes in market conditions could materially affect the portfolio’s value in the near term. We regularly monitor our portfolio for price changes, which might indicate potential impairments, and perform detailed reviews of securities with unrealized losses. In such cases, changes in fair value are evaluated to determine the extent to which such changes are attributable to: (i) fundamental factors specific to the issuer, such as financial condition, business prospects, or other factors, (ii) market-related factors, such as interest rates or equity market declines, or (iii) credit-related losses, where the present value of cash flows expected to be collected are lower than the amortized cost basis of the security.
	We analyze our debt securities that are in a loss position to determine if we intend to sell, or if it is more likely than not that we will be required to sell, the security prior to recovery and, if so, we write down the security to its current fair value, with the entire amount of the write-down recorded to earnings. To the extent that it is more likely than not that we will hold the debt security until recovery (which could be maturity), we determine if any of the decline in value is due to a credit loss (i.e., where the present value of future cash flows expected to be collected is lower than the amortized cost basis of the security) and, if so, we recognize that portion of the impairment as a component of net realized gains (losses) in the comprehensive income statement, with the difference (i.e., non-credit related impairment) recognized as part of our net unrealized gains (losses) in accumulated other comprehensive income. When an equity security (common equity and nonredeemable preferred stock) in our investment portfolio has an unrealized loss in fair value that is deemed to be other-than-temporary, we reduce the book value of such security to its current fair value, recognizing the decline as a realized loss in the comprehensive income statement. Any future changes in fair value, either increases or decreases, are reflected as changes in unrealized gains (losses) as part of accumulated other comprehensive income.
	Investment income consists of interest, dividends, and amortization. In addition to the discussion above for asset-backed securities, interest is recognized on an accrual basis using the effective yield method. Depending on the nature of the equity instruments, dividends are recorded at either the ex-dividend date or on an accrual basis.
	Realized gains (losses) on securities are computed based on the first-in first-out method and include write-downs on available-for-sale securities considered to have other-than-temporary declines in fair value (excluding non-credit related impairments), as well as holding period valuation changes on derivatives, trading securities, and hybrid instruments (e.g., securities with embedded options, where the option is a feature of the overall change in the value of the instrument).
Insurance Premiums and Receivables Policy	Insurance Premiums and Receivables  Insurance premiums written are earned into income on a pro rata basis over the period of risk, based on a daily earnings convention. Accordingly, unearned premiums represent the portion of premiums written that are applicable to the unexpired risk. We provide insurance and related services to individuals and small commercial accounts and offer a variety of payment plans. Generally, premiums are collected prior to providing risk coverage, minimizing our exposure to credit risk. We perform a policy level evaluation to determine the extent to which the premiums receivable balance exceeds the unearned premiums balance. We then age this exposure to establish an allowance for doubtful accounts based on prior experience.
Deferred Acquisition Costs Policy	Deferred Acquisition Costs  Deferred acquisition costs include commissions, premium taxes, and other variable underwriting and direct sales costs incurred in connection with the successful acquisition or renewal of insurance contracts. These acquisition costs are deferred and amortized over the policy period in which the related premiums are earned. We consider anticipated investment income in determining the recoverability of these costs. Management believes that these costs will be fully recoverable in the near term.
	We do not defer any advertising costs.
Reserve For Losses And Loss Adjustment Expenses	Loss and Loss Adjustment Expense Reserves  Loss reserves represent the estimated liability on claims reported to us, plus reserves for losses incurred but not recorded (IBNR). These estimates are reported net of amounts estimated to be recoverable from salvage and subrogation. Loss adjustment expense reserves represent the estimated expenses required to settle these claims and losses. The methods of making estimates and establishing these reserves are reviewed regularly, and resulting adjustments are reflected in income in the current period. Such loss and loss adjustment expense reserves are susceptible to change in the near term.
Reinsurance Policy	Reinsurance  Our reinsurance transactions primarily include premiums ceded to state-provided reinsurance facilities (e.g., Michigan Catastrophic Claims Association and North Carolina Reinsurance Facility) and premiums written under state-mandated involuntary plans for commercial vehicles (Commercial Auto Insurance Procedures/Plans – “CAIP”). Prepaid reinsurance premiums are earned on a pro rata basis over the period of risk, based on a daily earnings convention, which is consistent with premiums written. See Note 7 – Reinsurance for further discussion.
Income Tax Policy	Income Taxes  The income tax provision is calculated under the balance sheet approach. Deferred tax assets and liabilities are recorded based on the difference between the financial statement and tax bases of assets and liabilities at the enacted tax rates. The principal items giving rise to such differences are investment securities (e.g., net unrealized gains (losses), write-downs on securities determined to be other-than-temporarily impaired, and derivative instruments), loss and loss adjustment expense reserves, unearned premiums reserves, deferred acquisition costs, property and equipment, and non-deductible accruals. We review our deferred tax assets regularly for recoverability. See Note 5 – Income Taxes for further discussion.
Property, Plant and Equipment Policy	Property and Equipment  Property and equipment are recorded at cost, less accumulated depreciation, and include capitalized software developed or acquired for internal use. Depreciation is recognized over the estimated useful lives of the assets using accelerated methods for computer equipment and the straight-line method for all other fixed assets. The useful life for computer equipment and laptop computers is 3 years. The useful lives range from 7 to 40 years for buildings, improvements, and integrated components and 3 to 15 years for all other property and equipment. Land and buildings comprised 77% and 76% of total property and equipment at December 31, 2014 and 2013, respectively.
	During 2014, decisions were made to sell one property originally purchased for a future Service Center site. At December 31, 2014, included in other assets in the consolidated balance sheets is $8.7 million of "held for sale" property, which represents the fair value of this property less the estimated costs to sell.
Guaranty Fund Assessments Policy	Guaranty Fund Assessments  We are subject to state guaranty fund assessments, which provide for the payment of covered claims or other insurance obligations of insurance companies deemed insolvent. These assessments are accrued after a formal determination of insolvency has occurred, and we have written the premiums on which the assessments will be based.
Fees and Other Revenues	Fees and Other Revenues  Fees and other revenues primarily represent fees collected from policyholders relating to installment charges in accordance with our bill plans, as well as late payment and insufficient funds fees. Other revenues may include revenue from the sale of tax credits, rental income, and other revenue transactions.
Non-Insurance Service Business	Service Revenues and Expenses  Our service businesses provide insurance-related services. Service revenues generated from processing business for involuntary CAIP plans are earned on a pro rata basis over the term of the related policies. Service expenses related to these CAIP plans include acquisition expenses, which are deferred and amortized over the period in which the related revenues are earned. Other service business revenues and expenses are recorded in the period in which they are earned or incurred.
Equity-Based Compensation	Equity-Based Compensation  We currently issue time-based and performance-based restricted stock unit awards to key members of management as our form of equity compensation, and time-based restricted stock awards to non-employee directors. Prior to 2010, we issued restricted stock awards, instead of restricted stock unit awards, to employees. Collectively, we refer to these awards as “restricted equity awards.” We currently do not issue stock options as a form of equity compensation, and no such awards remain outstanding. Compensation expense for time-based restricted equity awards with installment vesting is recognized over each respective vesting period. For performance-based restricted equity awards, compensation expense is recognized over the respective estimated vesting periods. Dividend equivalent units are credited
	to outstanding restricted units awards, both time-based and performance-based, at the time a dividend is paid to shareholders.
	We record an estimate for expected forfeitures of restricted equity awards based on our historical forfeiture rates. In addition, we shorten the vesting periods of certain restricted equity awards based on the “qualified retirement” provisions in our incentive compensation plans, under which (among other provisions) the vesting of 50% of outstanding time-based restricted equity awards will accelerate upon retirement if the participant is 55 years of age or older and satisfies certain years-of-service requirements. For time-based awards granted after February 2013, we modified our "qualified retirement" provisions to vest and distribute 50% of the unvested portion of the award upon reaching eligibility for a qualified retirement and shortly after the grant date for each subsequent award.
Net Income Per Share Policy	Net Income Per Share  Basic net income per share is computed using the weighted average number of common shares outstanding during the reporting period, excluding unvested time-based and performance-based restricted equity awards that are subject to forfeiture. Diluted net income per share includes common stock equivalents assumed outstanding during the period. Our common stock equivalents include the incremental shares assumed to be issued for:
	•	earned but unvested time-based restricted equity awards, and
	•	certain unvested performance-based restricted equity awards that satisfied contingency conditions for common stock equivalents during the period.
Cash Flow Supplemental Disclosure	Supplemental Cash Flow Information  Cash includes only bank demand deposits. Non-cash activity includes declared but unpaid dividends.
New Accounting Pronouncements	New Accounting Standards In May 2014, the Financial Accounting Standards Board (FASB) issued an accounting standard update (ASU) related to the accounting for revenue from contracts with customers. This standard is intended to help reduce diversity in practice and enhance comparability between entities related to revenue recognition and is effective for fiscal years beginning after December 15, 2016 (2017 for calendar-year companies). Since the accounting for insurance contracts is outside of the scope of this ASU, we do not expect this standard to have a significant impact on our financial condition, cash flows, or results of operations.
	In June 2014, the FASB issued an ASU related to the accounting for share-based payments when the terms of an employee award can be achieved after the requisite service period. To the extent an equity award contains provisions that permit an employee who leaves the company before the performance targets are reached to receive some or all of the benefits of the award if and as the award later vests, this standard requires companies to recognize the compensation cost during the employee's remaining service period. This standard is effective for fiscal years beginning after December 15, 2015 (2016 for calendar-year companies). We plan to adopt this standard prospectively.  Although this standard may require an acceleration of the expense recognition of our share-based payment awards, we do not expect it to have a significant impact on our financial condition, cash flows, or results of operations.
	In June 2014, the FASB also issued an ASU related to repurchase-to-maturity transactions, repurchase financings, and related disclosures. The intent is to clarify that repurchase-to-maturity transactions must be accounted for and disclosed as secured borrowings, rather than potentially accounted for as sales, as permissible under certain circumstances in the previous guidance. This guidance is effective for annual and interim periods after December 15, 2014 (2015 for calendar-year companies). We do not typically engage in these type of transactions; therefore, we do not expect this standard to have a significant impact on our financial condition, cash flows, or results of operations.

Reporting_And_Accounting_Polic2

Reporting And Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Advertising Costs	Total advertising costs, which are expensed as incurred, for the years ended December 31, were:
	(millions)	Advertising Costs
	2014	$	681.8
	2013	619.3
	2012	546.8
Interest Capitalized	Total capitalized interest, which primarily relates to capitalized software projects, for the years ended December 31, was:
	(millions)	Capitalized
		Interest
	2014	$	1.3
	2013	0.8
	2012	0.3
Equity-based Compensation and Related Tax Benefits	The total compensation expense recognized for our equity-based compensation for the years ended December 31, was:
	(millions)	2014		2013		2012
	Pretax expense	$	51.4	$	64.9	$	63.4
	Tax benefit	18		22.7		22.2
Supplemental Cash Flow Information	For the years ended December 31, we paid the following:
	(millions)	2014		2013		2012
	Income taxes	$	515	$	497	$	389.1
	Interest	116		122.3		135

Investments_Tables

Investments (Tables)	12 Months Ended
	Dec. 31, 2014
Investments Schedule [Abstract]
Investment Portfolio by Major Security Type	The following tables present the composition of our investment portfolio by major security type, consistent with our internal classification of how we manage, monitor, and measure the portfolio:
	($ in millions)	Cost			Gross Unrealized Gains			Gross Unrealized Losses			Net Realized Gains (Losses)1			Fair Value			% of Total Fair Value
	31-Dec-14
	Fixed maturities:
	U.S. government obligations	$	2,641.10		$	27.3		$	(1.3	)	$	0		$	2,667.10		14	%
	State and local government obligations	2,095.70			44.6			(1.1		)	0			2,139.20			11.2
	Foreign government obligations	14.2			0			0			0			14.2			0.1
	Corporate debt securities	2,813.90			32.9			(10.4		)	0.3			2,836.70			14.9
	Residential mortgage-backed securities	1,635.50			34.5			(10.8		)	(0.7		)	1,658.50			8.7
	Commercial mortgage-backed securities	2,278.70			39.3			(2.6		)	0.2			2,315.60			12.2
	Other asset-backed securities	1,634.90			3.8			(0.8		)	0.8			1,638.70			8.6
	Redeemable preferred stocks	260.2			24.7			(5.7		)	0			279.2			1.5
	Total fixed maturities	13,374.20			207.1			(32.7		)	0.6			13,549.20			71.2
	Equity securities:
	Nonredeemable preferred stocks	590.4			201.1			(6.4		)	42.4			827.5			4.4
	Common equities	1,289.20			1,213.20			(10.1		)	0			2,492.30			13.1
	Short-term investments	2,149.00			0			0			0			2,149.00			11.3
	Total portfolio2,3	$	17,402.80		$	1,621.40		$	(49.2	)	$	43		$	19,018.00		100	%
	($ in millions)	Cost			Gross Unrealized Gains			Gross Unrealized Losses			Net Realized Gains (Losses)1			Fair Value			% of Total Fair Value
	31-Dec-13
	Fixed maturities:
	U.S. government obligations	$	3,630.40		$	48.4		$	(16.6	)	$	0		$	3,662.20		20.3	%
	State and local government obligations	2,247.30			27.1			(18.4		)	0			2,256.00			12.5
	Foreign government obligations	15.6			0			0			0			15.6			0.1
	Corporate debt securities	2,885.00			60.4			(20.4		)	1.6			2,926.60			16.2
	Residential mortgage-backed securities	1,110.10			31.9			(14.1		)	0			1,127.90			6.2
	Commercial mortgage-backed securities	2,154.40			43.9			(37.8		)	0			2,160.50			12
	Other asset-backed securities	1,073.00			6.6			(2.1		)	0.2			1,077.70			6
	Redeemable preferred stocks	299.5			24.1			(9.7		)	0			313.9			1.7
	Total fixed maturities	13,415.30			242.4			(119.1		)	1.8			13,540.40			75
	Equity securities:
	Nonredeemable preferred stocks	445.7			258.7			(4.5		)	11.3			711.2			3.9
	Common equities	1,451.10			1,081.80			(2.4		)	0			2,530.50			14
	Short-term investments	1,272.60			0			0			0			1,272.60			7.1
	Total portfolio2,3	$	16,584.70		$	1,582.90		$	(126.0	)	$	13.1		$	18,054.70		100	%
	1 Represents net holding period gains (losses) on certain hybrid securities (discussed below).
	2 Our portfolio reflects the effect of unsettled security transactions and collateral on open derivative positions; at December 31, 2014, $31.3 million was included in "other liabilities," compared to $61.3 million at December 31, 2013.
	3 The total fair value of the portfolio included $1.9 billion and $1.8 billion at December 31, 2014 and 2013, respectively, of securities held in a consolidated, non-insurance subsidiary of the holding company, net of any unsettled security transactions.
Hybrid Securities	Included in our fixed-maturity and equity securities are hybrid securities, which are reported at fair value at December 31:
	(millions)	2014				2013
	Fixed maturities:
	Corporate debt securities	$	139.8			$	164.2
	Residential mortgage-backed securities	120.7				0
	Commercial mortgage-backed securities	31.2				0
	Other asset-backed securities	13.7				14.8
	Total fixed maturities	305.4				179
	Equity securities:
	Nonredeemable preferred stocks	122.3				60.3
	Total hybrid securities	$	427.7			$	239.3
Composition of Fixed Maturities by Maturity	The composition of fixed maturities by maturity at December 31, 2014, was:
	(millions)	Cost				Fair Value
	Less than one year	$	3,180.10			$	3,217.40
	One to five years	7,026.30				7,097.20
	Five to ten years	3,093.00				3,152.90
	Ten years or greater	59				65.9
	Total1	$	13,358.40			$	13,533.40
	1 Excludes $15.8 million related to our open interest rate swap positions.
Gross Unrealized Losses by Major Security	The following tables show the composition of gross unrealized losses by major security type and by the length of time that individual securities have been in a continuous unrealized loss position:
		Total No. of Sec.		Total			Gross Unrealized Losses			Less than 12 Months									12 Months or Greater
				Fair
	($ in millions)			Value						No. of Sec.		Fair			Unrealized Losses				No. of Sec.		Fair			Unrealized Losses
												Value									Value
	31-Dec-14
	Fixed maturities:
	U.S. government obligations	11		$	428.2		$	(1.3	)	5		$	150.7		$	(0.3	)		6		$	277.5		$	(1.0	)
	State and local government obligations	46		234.2			(1.1		)	28		177.9			(0.4		)		18		56.3			(0.7		)
	Corporate debt securities	53		843.2			(10.4		)	43		647.5			(6.1		)		10		195.7			(4.3		)
	Residential mortgage-backed securities	70		844.2			(10.8		)	33		465.2			(3.1		)		37		379			(7.7		)
	Commercial mortgage-backed securities	63		723.4			(2.6		)	54		667.5			(1.4		)		9		55.9			(1.2		)
	Other asset-backed securities	44		741.8			(0.8		)	42		715.7			(0.7		)		2		26.1			(0.1		)
	Redeemable preferred stocks	3		103			(5.7		)	1		33			(1.0		)		2		70			(4.7		)
	Total fixed maturities	290		3,918.00			(32.7		)	206		2,857.50			(13.0		)		84		1,060.50			(19.7		)
	Equity securities:
	Nonredeemable preferred stocks	8		231.4			(6.4		)	5		143.2			(3.6		)		3		88.2			(2.8		)
	Common equities	20		68.4			(10.1		)	19		61.8			(9.6		)		1		6.6			(0.5		)
	Total equity securities	28		299.8			(16.5		)	24		205			(13.2		)		4		94.8			(3.3		)
	Total portfolio	318		$	4,217.80		$	(49.2	)	230		$	3,062.50		$	(26.2	)		88		$	1,155.30		$	(23.0	)
		Total No. of Sec.		Total			Gross			Less than 12 Months									12 Months or Greater
				Fair			Unrealized
	($ in millions)			Value			Losses			No. of Sec.		Fair			Unrealized				No. of Sec.		Fair			Unrealized
												Value			Losses						Value			Losses
	31-Dec-13
	Fixed maturities:
	U.S. government obligations	29		$	1,444.30		$	(16.6	)	28		$	1,434.60		$	(16.3	)		1		$	9.7		$	(0.3	)
	State and local government obligations	141		844.2			(18.4		)	119		759.3			(17.1		)		22		84.9			(1.3		)
	Corporate debt securities	51		997.6			(20.4		)	45		831.1			(17.8		)		6		166.5			(2.6		)
	Residential mortgage-backed securities	66		763.5			(14.1		)	45		597.6			(7.9		)		21		165.9			(6.2		)
	Commercial mortgage-backed securities	76		1,061.90			(37.8		)	60		809.2			(19.7		)		16		252.7			(18.1		)
	Other asset-backed securities	25		287.2			(2.1		)	22		233.3			(1.8		)		3		53.9			(0.3		)
	Redeemable preferred stocks	4		122.7			(9.7		)	0		0			0				4		122.7			(9.7		)
	Total fixed maturities	392		5,521.40			(119.1		)	319		4,665.10			(80.6		)		73		856.3			(38.5		)
	Equity securities:
	Nonredeemable preferred stocks	7		142.3			(4.5		)	7		142.3			(4.5		)		0		0			0
	Common equities	24		59.7			(2.4		)	20		58.5			(2.4		)		4		1.2			0
	Total equity securities	31		202			(6.9		)	27		200.8			(6.9		)		4		1.2			0
	Total portfolio	423		$	5,723.40		$	(126.0	)	346		$	4,865.90		$	(87.5	)		77		$	857.5		$	(38.5	)
Total Non-Credit Portion of Other-Than-Temporary Impairment Recorded in Accumulated Other Comprehensive Income, Reflecting Orginal Non-Credit Loss at the Time Credit Impairment	The following table shows the total non-credit portion of the OTTI recorded in accumulated other comprehensive income, reflecting the original non-credit loss at the time the credit impairment was determined:
		December 31,
	(millions)	2014			2013
	Fixed maturities:
	Residential mortgage-backed securities	$	(44.1	)	$	(44.1	)
	Commercial mortgage-backed securities	(0.6		)	(0.9		)
	Total fixed maturities	$	(44.7	)	$	(45.0	)
OTTI Credit Losses Recognized in Earnings	The following tables provide rollforwards of the amounts related to credit losses recognized in earnings for the periods ended December 31, 2014, 2013, and 2012, for which a portion of the OTTI losses were also recognized in accumulated other comprehensive income at the time the credit impairments were determined and recognized:
	(millions)	Residential			Commercial			Total
		Mortgage-			Mortgage-
		Backed			Backed
	Balance at December 31, 2013	$	19.2		$	0.4		$	19.6
	Credit losses for which an OTTI was previously recognized	0			0			0
	Credit losses for which an OTTI was not previously recognized	0			0			0
	Reductions for securities sold/matured	(0.1		)	0			(0.1		)
	Change in recoveries of future cash flows expected to be collected1,2	(6.4		)	0			(6.4		)
	Reductions for previously recognized credit impairments	0			0			0
	written-down to fair value3
	Balance at December 31, 2014	$	12.7		$	0.4		$	13.1
	(millions)	Residential			Commercial			Total
		Mortgage-			Mortgage-
		Backed			Backed
	Balance at December 31, 2012	$	27.1		$	0.6		$	27.7
	Credit losses for which an OTTI was previously recognized	0.1			0			0.1
	Credit losses for which an OTTI was not previously recognized	0			0			0
	Reductions for securities sold/matured	0			0			0
	Change in recoveries of future cash flows expected to be collected1,2	(7.8		)	(0.2		)	(8.0		)
	Reductions for previously recognized credit impairments	(0.2		)	0			(0.2		)
	written-down to fair value3
	Balance at December 31, 2013	$	19.2		$	0.4		$	19.6
	(millions)	Residential			Commercial			Total
		Mortgage-			Mortgage-
		Backed			Backed
	Balance at December 31, 2011	$	34.5		$	1.3		$	35.8
	Credit losses for which an OTTI was previously recognized	0.1			0			0.1
	Credit losses for which an OTTI was not previously recognized	0.3			0			0.3
	Reductions for securities sold/matured	0			(0.2		)	(0.2		)
	Change in recoveries of future cash flows expected to be collected1,2	(3.8		)	(0.2		)	(4.0		)
	Reductions for previously recognized credit impairments	(4.0		)	(0.3		)	(4.3		)
	written-down to fair value3
	Balance at December 31, 2012	$	27.1		$	0.6		$	27.7
	1 Reflects expected recovery of prior period impairments that will be accreted into income over the remaining life of the security.
	2 Includes $4.3 million, $2.6 million, and $1.4 million at December 31, 2014, 2013, and 2012, respectively, recognized in income in excess of the cash flows expected to be collected at the time of the write-downs.
	3 Reflects reductions of prior credit impairments where the current credit impairment requires writing securities down to fair value (i.e., no remaining non-credit loss).
Components of Net Realized Gains (Losses)	The components of net realized gains (losses) for the years ended December 31, were:
	(millions)	2014			2013			2012
	Gross realized gains on security sales
	Fixed maturities:
	U.S. government obligations	$	24		$	8.5		$	20.2
	State and local government obligations	9.3			7.7			15
	Corporate and other debt securities	37.2			47.7			58.1
	Residential mortgage-backed securities	2.7			3			1.2
	Commercial mortgage-backed securities	17			10			19.3
	Other asset-backed securities	0			0			0.9
	Redeemable preferred stocks	2.7			0			0.7
	Total fixed maturities	92.9			76.9			115.4
	Equity securities:
	Nonredeemable preferred stocks	90			126.3			78.2
	Common equities	107.3			68.6			167
	Subtotal gross realized gains on security sales	290.2			271.8			360.6
	Gross realized losses on security sales
	Fixed maturities:
	U.S. government obligations	(7.6		)	(3.7		)	(1.9		)
	State and local government obligations	(0.5		)	0			0
	Corporate and other debt securities	(2.8		)	(6.2		)	(0.6		)
	Residential mortgage-backed securities	(0.2		)	0			0
	Commercial mortgage-backed securities	(8.3		)	(1.8		)	0
	Redeemable preferred stocks	(3.2		)	(0.1		)	(0.4		)
	Total fixed maturities	(22.6		)	(11.8		)	(2.9		)
	Equity securities:
	Nonredeemable preferred stocks	0			(0.1		)	(1.1		)
	Common equities	(7.3		)	(0.6		)	(27.1		)
	Subtotal gross realized losses on security sales	(29.9		)	(12.5		)	(31.1		)
	Net realized gains (losses) on security sales
	Fixed maturities:
	U.S. government obligations	16.4			4.8			18.3
	State and local government obligations	8.8			7.7			15
	Corporate and other debt securities	34.4			41.5			57.5
	Residential mortgage-backed securities	2.5			3			1.2
	Commercial mortgage-backed securities	8.7			8.2			19.3
	Other asset-backed securities	0			0			0.9
	Redeemable preferred stocks	(0.5		)	(0.1		)	0.3
	Total fixed maturities	70.3			65.1			112.5
	Equity securities:
	Nonredeemable preferred stocks	90			126.2			77.1
	Common equities	100			68			139.9
	Subtotal net realized gains (losses) on security sales	260.3			259.3			329.5
	Other-than-temporary impairment losses
	Fixed maturities:
	Residential mortgage-backed securities	0			(0.6		)	(1.6		)
	Commercial mortgage-backed securities	0			0			(0.1		)
	Total fixed maturities	0			(0.6		)	(1.7		)
	Equity securities:
	Common equities	(7.2		)	(5.5		)	(1.8		)
	Subtotal other-than-temporary impairment losses	(7.2		)	(6.1		)	(3.5		)
	Other gains (losses)
	Hybrid securities	30.5			6.4			14.3
	Derivative instruments	(64.1		)	56.6			(43.1		)
	Litigation settlements	4.7			2.2			9.6
	Subtotal other gains (losses)	(28.9		)	65.2			(19.2		)
	Total net realized gains (losses) on securities	$	224.2		$	318.4		$	306.8
Components of Net Investment Income	The components of net investment income for the years ended December 31, were:
	(millions)	2014			2013			2012
	Fixed maturities:
	U.S. government obligations	$	46.2		$	50.2		$	49.8
	State and local government obligations	50.1			48			51.1
	Foreign government obligations	0.4			0.2			0
	Corporate debt securities	82.1			98.8			107.5
	Residential mortgage-backed securities	44.9			28.1			16.1
	Commercial mortgage-backed securities	66			74.8			82.2
	Other asset-backed securities	16.7			16.7			20.3
	Redeemable preferred stocks	15.5			21.2			24.2
	Total fixed maturities	321.9			338			351.2
	Equity securities:
	Nonredeemable preferred stocks	38.6			36.2			43.8
	Common equities	46.6			45.8			44.9
	Short-term investments	1.3			2			3.1
	Investment income	408.4			422			443
	Investment expenses	(18.9		)	(18.8		)	(15.4		)
	Net investment income	$	389.5		$	403.2		$	427.6
Derivative Instruments	The following table shows the status of our derivative instruments at December 31, 2014 and 2013, and for the years ended December 31, 2014, 2013, and 2012:
	(millions)											Balance Sheet2							Comprehensive
																			Income Statement
		Notional Value1											Assets						Pretax Net Realized
													(Liabilities)						Gains (Losses)
													Fair Value
																			Years ended
		December 31,											December 31,						December 31,
	Derivatives	2014			2013			2012			Purpose	Classification	2014			2013			2014			2013			2012
	designated as:
	Hedging instruments
	Closed:
	Ineffective cash flow hedge	$	44		$	54		$	31		Manage	NA	$	0		$	0		$	0.5		$	0.8		$	0.6
											interest
											rate risk
	Non-hedging instruments
	Assets:
	Interest rate swaps	750			750			0			Manage portfolio duration	Investments - fixed	15.8			68.1			(64.6		)	59.8			0
												maturities
	Liabilities:
	Interest rate swaps	0			0			1,263			Manage	Other liabilities	0			0			0			0			(42.7		)
											portfolio
											duration
	Closed:
	Interest rate swaps	0			1,263			0			Manage	NA	0			0			0			(4.0		)	0
											portfolio
											duration
	Corporate credit default swaps	0			0			25			Manage	NA	0			0			0			0			(1.0		)
											credit
											risk
	Total	NA			NA			NA					$	15.8		$	68.1		$	(64.1	)	$	56.6		$	(43.1	)
	NA =ot Applicable
	1 The amounts represent the value held at year end for open positions and the maximum amount held during the year for closed positions.
	2 To the extent we hold both derivative assets and liabilities with the same counterparty that are subject to an enforceable master netting arrangement, we expect that we will report them on a gross basis on our balance sheets, consistent with our historical presentation.

Fair_Value_Tables

Fair Value (Tables)	12 Months Ended
	Dec. 31, 2014
Fair Value Disclosures [Abstract]
Composition of Investment Portfolio by Major Security Type	The composition of the investment portfolio by major security type was:
		Fair Value
	(millions)	Level 1		Level 2			Level 3		Total			Cost
	31-Dec-14
	Fixed maturities:
	U.S. government obligations	$	2,667.10	$	0		$	0	$	2,667.10		$	2,641.10
	State and local government obligations	0		2,139.20			0		2,139.20			2,095.70
	Foreign government obligations	14.2		0			0		14.2			14.2
	Corporate debt securities	0		2,836.70			0		2,836.70			2,813.90
	Subtotal	2,681.30		4,975.90			0		7,657.20			7,564.90
	Asset-backed securities:
	Residential mortgage-backed	0		1,658.50			0		1,658.50			1,635.50
	Commercial mortgage-backed	0		2,304.00			11.6		2,315.60			2,278.70
	Other asset-backed	0		1,638.70			0		1,638.70			1,634.90
	Subtotal asset-backed securities	0		5,601.20			11.6		5,612.80			5,549.10
	Redeemable preferred stocks:
	Financials	0		97.9			0		97.9			77.3
	Utilities	0		65.3			0		65.3			65
	Industrials	0		116			0		116			117.9
	Subtotal redeemable preferred stocks	0		279.2			0		279.2			260.2
	Total fixed maturities	2,681.30		10,856.30			11.6		13,549.20			13,374.20
	Equity securities:
	Nonredeemable preferred stocks:
	Financials	204.1		554.1			69.3		827.5			590.4
	Utilities	0		0			0		0			0
	Subtotal nonredeemable preferred stocks	204.1		554.1			69.3		827.5			590.4
	Common equities:
	Common stocks	2,491.90		0			0		2,491.90			1,288.80
	Other risk investments	0		0			0.4		0.4			0.4
	Subtotal common equities	2,491.90		0			0.4		2,492.30			1,289.20
	Total fixed maturities and equity securities	5,377.30		11,410.40			81.3		16,869.00			15,253.80
	Short-term investments	1,937.00		212			0		2,149.00			2,149.00
	Total portfolio	$	7,314.30	$	11,622.40		$	81.3	$	19,018.00		$	17,402.80
	Debt	$	0	$	2,527.50		$	0	$	2,527.50		$	2,164.70
		Fair Value
	(millions)	Level 1		Level 2			Level 3		Total			Cost
	31-Dec-13
	Fixed maturities:
	U.S. government obligations	$	3,662.20	$	0		$	0	$	3,662.20		$	3,630.40
	State and local government obligations	0		2,256.00			0		2,256.00			2,247.30
	Foreign government obligations	15.6		0			0		15.6			15.6
	Corporate debt securities	0		2,926.60			0		2,926.60			2,885.00
	Subtotal	3,677.80		5,182.60			0		8,860.40			8,778.30
	Asset-backed securities:
	Residential mortgage-backed	0		1,127.70			0.2		1,127.90			1,110.10
	Commercial mortgage-backed	0		2,131.50			29		2,160.50			2,154.40
	Other asset-backed	0		1,077.70			0		1,077.70			1,073.00
	Subtotal asset-backed securities	0		4,336.90			29.2		4,366.10			4,337.50
	Redeemable preferred stocks:
	Financials	0		102.8			0		102.8			84.2
	Utilities	0		65.6			0		65.6			64.9
	Industrials	0		145.5			0		145.5			150.4
	Subtotal redeemable preferred stocks	0		313.9			0		313.9			299.5
	Total fixed maturities	3,677.80		9,833.40			29.2		13,540.40			13,415.30
	Equity securities:
	Nonredeemable preferred stocks:
	Financials	240.8		414.6			39		694.4			431.5
	Utilities	0		16.8			0		16.8			14.2
	Subtotal nonredeemable preferred stocks	240.8		431.4			39		711.2			445.7
	Common equities:
	Common stocks	2,530.00		0			0		2,530.00			1,450.60
	Other risk investments	0		0			0.5		0.5			0.5
	Subtotal common equities	2,530.00		0			0.5		2,530.50			1,451.10
	Total fixed maturities and equity securities	6,448.60		10,264.80			68.7		16,782.10			15,312.10
Short-term investments	987.8		284.8			0		1,272.60			1,272.60
Total portfolio	$	7,436.40	$	10,549.60		$	68.7	$	18,054.70		$	16,584.70
Debt	$	0	$	2,073.70		$	0	$	2,073.70		$	1,860.90
Summary of Changes in Fair Value Associated With Level 3 Assets	The following tables provide a summary of changes in fair value associated with Level 3 assets for the years ended December 31, 2014 and 2013:
		Level 3 Fair Value
	(millions)	Fair Value at Dec. 31, 2013		Calls/			Purchases		Sales			Net Realized			Change in			Net			Fair Value at Dec. 31, 2014
				Maturities/								(Gain)/Loss			Valuation			Transfers
				Paydowns								on Sales						In (Out)1
	Fixed maturities:
	Asset-backed securities:
	Residential mortgage-backed	$	0.2	$	0		$	0	$	(0.1	)	$	0.1		$	(0.2	)	$	0		$	0
	Commercial mortgage-backed	29		(3.6		)	0		0			0			(0.2		)	(13.6		)	11.6
	Total fixed maturities	29.2		(3.6		)	0		(0.1		)	0.1			(0.4		)	(13.6		)	11.6
	Equity securities:
	Nonredeemable preferred stocks:
	Financials2	39		0			0		0			0			30.3			0			69.3
	Common equities:
	Other risk investments	0.5		(0.1		)	0		0			0			0			0			0.4
	Total Level 3 securities	$	68.7	$	(3.7	)	$	0	$	(0.1	)	$	0.1		$	29.9		$	(13.6	)	$	81.3
	1 The $13.6 million was transferred out of Level 3 and into Level 2 due to an improvement in the security's underlying collateral and an increase in liquidity and market activity in comparable securities.
	2 The $30.3 million represents a net holding period gain on our investment in ARX Holding Corp., which is reflected in net realized gains (losses) on securities in the comprehensive income statement.
		Level 3 Fair Value
	(millions)	Fair Value at Dec. 31, 2012		Calls/			Purchases		Sales			Net Realized			Change in			Net			Fair Value at Dec. 31, 2013
				Maturities/								(Gain)/Loss			Valuation			Transfers
				Paydowns								on Sales						In (Out)1
	Fixed maturities:
	Asset-backed securities:
	Residential mortgage-backed	$	45.5	$	(28.6	)	$	125.1	$	0		$	0		$	(0.4	)	$	(141.4	)	$	0.2
	Commercial mortgage-backed	25.3		(3.4		)	0		0			0			7.1			0			29
	Total fixed maturities	70.8		(32.0		)	125.1		0			0			6.7			(141.4		)	29.2
	Equity securities:
	Nonredeemable preferred stocks:
	Financials2	31.9		0			0		0			0			7.1			0			39
	Common equities:
	Other risk investments	12		(0.5		)	0.3		(2.4		)	(36.0		)	27.1			0			0.5
	Total Level 3 securities	$	114.7	$	(32.5	)	$	125.4	$	(2.4	)	$	(36.0	)	$	40.9		$	(141.4	)	$	68.7
	1 The $141.4 million was transferred out of Level 3 and into Level 2 due to an increase in liquidity and trading volume in the market.
	2 The $7.1 million represents a net holding period gain on our investment in ARX Holding Corp., which is reflected in net realized gains (losses) on securities in the comprehensive income statement.
Summary of Quantitative Information about Level 3 Fair Value Measurements	The following table provides a summary of the quantitative information about Level 3 fair value measurements for our applicable securities at December 31:
		Quantitative Information about Level 3 Fair Value Measurements
	($ in millions)	Fair Value at Dec. 31, 2014		Valuation Technique	Unobservable Input	Unobservable Input Assumption
	Fixed maturities:
	Asset-backed securities:
	Residential mortgage-backed	$	0	NA	NA	NA
	Commercial mortgage-backed	11.6		External vendor	Prepayment rate1	0
	Total fixed maturities	11.6
	Equity securities:
	Nonredeemable preferred stocks:
	Financials	69.3		Multiple of tangible net book value	Price to book ratio multiple	2.6
	Subtotal Level 3 securities	80.9
	Third-party pricing exemption securities2	0.4
	Total Level 3 securities	$	81.3
	NA=ot Applicable since we did not hold any residential mortgage-backed Level 3 securities at December 31, 2014.
	1 Assumes that one security has 0% of the principal amount of the underlying loans that will be paid off prematurely in each year.
	2 The fair values for these securities were obtained from non-binding external sources where unobservable inputs are not reasonably available to us.
		Quantitative Information about Level 3 Fair Value Measurements
	($ in millions)	Fair Value at Dec. 31, 2013		Valuation Technique	Unobservable Input	Unobservable Input Assumption
	Fixed maturities:
	Asset-backed securities:
	Residential mortgage-backed	$	0.2	External vendor	Prepayment rate1	0
	Commercial mortgage-backed	29		External vendor	Prepayment rate2	0
	Total fixed maturities	29.2
	Equity securities:
	Nonredeemable preferred stocks:
	Financials	39		Multiple of tangible net book value	Price to book ratio multiple	1.9
	Subtotal Level 3 securities	68.2
	Third-party pricing exemption securities3	0.5
	Total Level 3 securities	$	68.7
	1 Assumes that one security has 0% of the principal amount of the underlying loans that will be paid off prematurely in each year.
	2 Assumes that two securities have 0% of the principal amount of the underlying loans that will be paid off prematurely in each year.
	3 The fair values for these securities were obtained from non-binding external sources where unobservable inputs are not reasonably available to us.

Debt_Tables

Debt (Tables)	12 Months Ended
	Dec. 31, 2014
Debt Table	Debt at December 31 consisted of:
		2014						2013
	(millions)	Carrying			Fair			Carrying		Fair
		Value			Value			Value		Value
	3.75% Senior Notes due 2021 (issued: $500.0, August 2011)	$	497.8		$	535.6		$	497.6	$	509.1
	6 5/8% Senior Notes due 2029 (issued: $300.0, March 1999)	295.5			400.6			295.3		359.6
	6.25% Senior Notes due 2032 (issued: $400.0, November 2002)	394.8			527.9			394.6		473.7
	4.35% Senior Notes due 2044 (issued: $350.0, April 2014)	346.3			378.9			0		0
	6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067 (issued: $1,000.0, June 2007; outstanding: $632.8 and $677.1)	630.3			684.5			673.4		731.3
	Total	$	2,164.70		$	2,527.50		$	1,860.90	$	2,073.70
Aggregate Principal Payments on Debt Outstanding	Aggregate required principal payments on debt outstanding are as follows:
	(millions)
	Year	Payments
	2015	$	0
	2016	0
	2017	0
	2018	0
	2019	0
	Thereafter	2,182.80
	Total	$	2,182.80
Cash Flow Hedging
Unrealized Gain (Loss) on Interest Rate Cash Flow Hedges Included in Accumulated Other Comprehensive Income	The original unrealized gain (loss) at the time of each debt issuance and the unamortized balance at December 31, 2014, on a pretax basis, of these hedges, were as follows:
	(millions)	Unrealized Gain (Loss)			Unamortized Balance
		at Debt Issuance			at December 31, 2014
	3.75% Senior Notes	$	(5.1	)	$	(3.6	)
	6 5/8% Senior Notes	(4.2		)	(3.2		)
	6.25% Senior Notes	5.1			4
	4.35% Senior Notes	(1.6		)	(1.6		)
	6.70% Debentures	34.4			6.6

Income_Taxes_Tables

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Components of Income Tax Provision	The components of our income tax provision were as follows:
	(millions)	2014			2013			2012
	Current tax provision	$	594.4		$	460.2		$	424.8
	Deferred tax expense (benefit)	32			94.4			(9.4		)
	Total income tax provision	$	626.4		$	554.6		$	415.4
Reconciliation of Provision (Benefit) for Income Taxes Reported in Consolidated Statements of Income with Tax at Statutory Rate	The provision for income taxes in the accompanying consolidated statements of comprehensive income differed from the statutory rate as follows:
	($ in millions)	2014						2013					2012
	Income before income taxes	$	1,907.40					$	1,720.00				$	1,317.70
	Tax at statutory rate	$	667.6		35	%		$	602		35	%	$	461.2		35	%
	Tax effect of:
	Dividends received deduction	(18.3		)	(1	)		(17.6		)	(1	)	(18.2		)	(1	)
	Exempt interest income	(13.8		)	(1	)		(13.1		)	(1	)	(14.7		)	(1	)
	Tax-deductible dividends	(6.5		)	0			(13.6		)	(1	)	(11.9		)	(1	)
	Tax credits	(2.2		)	0			(2.3		)	0		0			0
	Other items, net	(0.4		)	0			(0.8		)	0		(1.0		)	0
	Total income tax provision	$	626.4		33	%		$	554.6		32	%	$	415.4		32	%
Components of Net Deferred Tax Assets	At December 31, 2014 and 2013, the components of the net deferred tax asset (liability) were as follows:
	(millions)	2014			2013
	Deferred tax assets:
	Unearned premiums reserve	$	378.8		$	361
	Investment basis differences	60.6			94.8
	Non-deductible accruals	208			200.7
	Loss and loss adjustment expense reserves	76.9			92
	Other	7.5			14.7
	Deferred tax liabilities:
	Net unrealized gains on securities	(550.3		)	(509.9		)
	Hedges on forecasted transactions	(0.8		)	(2.2		)
	Deferred acquisition costs	(160.0		)	(156.7		)
	Property and equipment	(100.9		)	(99.6		)
	Prepaid expenses	(11.4		)	(14.4		)
	Deferred gain on extinguishment of debt	(3.0		)	(4.8		)
	Other	(4.3		)	(4.0		)
	Net deferred tax liability	$	(98.9	)	$	(28.4	)

Loss_And_Loss_Adjustment_Expen1

Loss And Loss Adjustment Expense Reserves (Tables)	12 Months Ended
	Dec. 31, 2014
Loss and Loss Adjustment Expense Reserves Disclosures [Abstract]
Activity in Loss and Loss Adjustment Expense Reserves	Activity in the loss and loss adjustment expense reserves is summarized as follows:
	(millions)	2014			2013		2012
	Balance at January 1	$	8,479.70		$	7,838.40	$	7,245.80
	Less reinsurance recoverables on unpaid losses	1,045.90			862.1		785.7
	Net balance at January 1	7,433.80			6,976.30		6,460.10
	Incurred related to:
	Current year	13,330.30			12,427.30		11,926.00
	Prior years	(24.1		)	45.1		22
	Total incurred	13,306.20			12,472.40		11,948.00
	Paid related to:
	Current year	8,831.50			8,095.00		7,895.30
	Prior years	4,237.00			3,919.90		3,536.50
	Total paid	13,068.50			12,014.90		11,431.80
	Net balance at December 31	7,671.50			7,433.80		6,976.30
	Plus reinsurance recoverables on unpaid losses	1,185.90			1,045.90		862.1
	Balance at December 31	$	8,857.40		$	8,479.70	$	7,838.40

Reinsurance_Tables

Reinsurance (Tables)	12 Months Ended
	Dec. 31, 2014
Reinsurance Disclosures [Abstract]
Effect of Reinsurance on Premiums Written and Earned	The effect of reinsurance on premiums written and earned for the years ended December 31, was as follows:
		2014							2013							2012
	(millions)	Written			Earned				Written			Earned				Written			Earned
	Direct premiums	$	18,914.80		$	18,648.40			$	17,562.80		$	17,317.90			$	16,558.80		$	16,207.60
	Ceded	(260.2		)	(249.9		)		(223.1		)	(214.5		)		(186.1		)	(189.6		)
	Net premiums	$	18,654.60		$	18,398.50			$	17,339.70		$	17,103.40			$	16,372.70		$	16,018.00
Prepaid Reinsurance Premiums and Reinsurance Recoverables	Our prepaid reinsurance premiums and reinsurance recoverables were comprised of the following at December 31:
		Prepaid Reinsurance Premiums												Reinsurance Recoverables
	($ in millions)	2014						2013						2014						2013
	MCCA	$	32.8		38	%		$	29.5		40	%		$	1,018.80		83	%		$	875.9	80	%
	CAIP	26.5			31			21.1			28			110.1			9			79.3		7
	NCRF	21.9			26			20.5			27			51.1			4			50.1		5
	State Plans	81.2			95			71.1			95			1,180.00			96			1,005.30		92
	Non-State Plans	4.1			5			3.8			5			51.9			4			84.9		8
	Total	$	85.3		100	%		$	74.9		100	%		$	1,231.90		100	%		$	1,090.20	100	%

Employee_Benefit_Plans_Tables

Employee Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2014
Amounts Charged to Income for Employees Incentive Compensation Plans	The amounts charged to income for the incentive compensation plans for the years ended December 31, were:
		2014						2013							2012
	(millions)	Pretax			After Tax			Pretax			After Tax				Pretax		After Tax
	Cash	$	266.2		$	173		$	234.5		$	152.4			$	207	$	134.6
	Equity	51.4			33.4			64.9			42.2				63.4		41.2
Assets Held in Deferral Plan Irrevocable Grantor Trust Account	The Deferral Plan Irrevocable Grantor Trust account held the following assets at December 31:
	(millions)	2014			2013
	Progressive common shares1	$	83.2		$	57.1
	Other investment funds2	123.9			113.1
	Total	$	207.1		$	170.2
	1 Includes 3.6 million and 2.5 million common shares as of December 31, 2014 and 2013, respectively, to be distributed in common shares.
	2 Amount is included in other assets on the balance sheet.
Employee
Summary of Restricted Stock Activity	A summary of all employee restricted equity award activity during the years ended December 31, follows:
		2014					2013						2012
	Restricted Equity Awards	Number of Shares1		Weighted			Number of		Weighted				Number of		Weighted
				Average			Shares1		Average				Shares1		Average
				Grant					Grant						Grant
				Date Fair					Date Fair						Date Fair
				Value					Value						Value
	Beginning of year	9,918,575		$	20.13		11,625,981		$	17.8			12,296,847		$	16.86
	Add (deduct):
	Granted2	3,542,984		19.32			2,738,809		22.73				2,680,229		19.11
	Vested	(4,228,673	)	16.99			(4,293,605	)	15.54				(3,188,111	)	15.23
	Forfeited	(181,322	)	20.75			(152,610	)	18.28				(162,984	)	17.93
	End of year3,4	9,051,564		$	21.27		9,918,575		$	20.13			11,625,981		$	17.8
	1 Includes both restricted stock units and restricted stock. Upon vesting, all units will be converted on a one-for-one basis into Progressive common shares funded from existing treasury shares. All performance-based awards are included at their target amounts.
	2 In 2010, we began reinvesting dividend equivalents on restricted stock units. For 2014, 2013, and 2012, the number of units "granted" shown in the table above includes 538,749, 161,077, and 440,029 of dividend equivalent units, respectively, at a weighted average grant date fair value of $0, since the dividends were factored into the grant date fair value of the original grant.
	3 At December 31, 2014, the number of shares included 2,647,530 performance-based awards at their target amounts. We expect 2,208,731 of these performance-based awards to vest, based upon our current estimate of the likelihood of achieving these pre-determined performance goals.
	4 At December 31, 2014, the total unrecognized compensation cost related to unvested equity awards was $70.5 million, which includes performance-based awards at their currently estimated vesting value. This compensation expense will be recognized into the income statement over the weighted average vesting period of 2.3 years.
Director
Summary of Restricted Stock Activity	A summary of all directors’ restricted stock activity during the years ended December 31, follows:
		2014					2013						2012
	Restricted Stock	Number of		Weighted			Number of		Weighted				Number of		Weighted
		Shares		Average			Shares		Average				Shares		Average
				Grant					Grant						Grant
				Date Fair					Date Fair						Date Fair
				Value					Value						Value
	Beginning of year	93,254		$	26.19		92,957		$	21.41			94,106		$	21.8
	Add (deduct):
	Granted	90,649		25.44			93,254		26.19				92,957		21.41
	Vested	(93,254	)	26.19			(92,957	)	21.41				(94,106	)	21.8
	Forfeited	(9,070	)	25.36			0		0				0		0
	End of year	81,579		$	25.45		93,254		$	26.19			92,957		$	21.41

Segment_Information_Tables

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2014
Segment Reporting [Abstract]
Reconciliation of Revenue and Operating Income from Segments to Consolidated	Following are the operating results for the years ended December 31:
		2014							2013						2012
	(millions)	Revenues			Pretax				Revenues			Pretax			Revenues			Pretax
					Profit							Profit						Profit
					(Loss)							(Loss)						(Loss)
	Personal Lines
	Agency	$	9,087.00		$	683			$	8,601.50		$	542.9		$	8,103.90		$	338.9
	Direct	7,474.00			423.4				6,740.10			473.9			6,264.20			289.5
	Total Personal Lines1	16,561.00			1,106.40				15,341.60			1,016.80			14,368.10			628.4
	Commercial Lines	1,837.50			315.8				1,761.60			114.1			1,649.00			86.3
	Other indemnity	0			(11.9		)		0.2			(10.8		)	0.9			(5.8		)
	Total underwriting operations	18,398.50			1,410.30				17,103.40			1,120.10			16,018.00			708.9
	Fees and other revenues2	309.1			NA				291.8			NA			281.8			NA
	Service businesses	56			5.1				39.6			0.8			36.1			0
	Investments3	632.6			613.7				740.4			721.6			749.8			734.4
	Gains (losses) on extinguishment of debt	(4.8		)	(4.8		)		(4.3		)	(4.3		)	(1.8		)	(1.8		)
	Interest expense	NA			(116.9		)		NA			(118.2		)	NA			(123.8		)
	Consolidated total	$	19,391.40		$	1,907.40			$	18,170.90		$	1,720.00		$	17,083.90		$	1,317.70
	NA =ot Applicable
	1 Personal auto insurance accounted for 92% of the total Personal Lines segment net premiums earned in 2014, compared to 91% in 2013 and 2012; insurance for our special lines products (e.g., motorcycles, ATVs, RVs, mobile homes, watercraft, and snowmobiles) accounted for the balance of the Personal Lines net premiums earned.
	2 Pretax profit (loss) for fees and other revenues are allocated to operating segments.
	3 Revenues represent recurring investment income and total net realized gains (losses) on securities; pretax profit is net of investment expenses.
Underwriting Margins and Combined Ratios for our Underwriting Operations	Following are the underwriting margins/combined ratios for our underwriting operations for the years ended December 31:
		2014				2013				2012
		Underwriting		Combined		Underwriting		Combined		Underwriting		Combined
		Margin		Ratio		Margin		Ratio		Margin		Ratio
	Personal Lines
	Agency	7.5	%	92.5		6.3	%	93.7		4.2	%	95.8
	Direct	5.7		94.3		7		93		4.6		95.4
	Total Personal Lines	6.7		93.3		6.6		93.4		4.4		95.6
	Commercial Lines	17.2		82.8		6.5		93.5		5.2		94.8
	Other indemnity1	NM		NM		NM		NM		NM		NM
	Total underwriting operations	7.7		92.3		6.5		93.5		4.4		95.6
	1 Underwriting margins/combined ratios are not meaningful (NM) for our other indemnity businesses due to the low level of premiums earned by, and the variability of loss costs in, such businesses.

Other_Comprehensive_Income_Los1

Other Comprehensive Income (Loss) (Tables)	12 Months Ended
	Dec. 31, 2014
Equity [Abstract]
Components of Other Comprehensive Income (Loss)	The components of other comprehensive income (loss) for the years ended December 31, were as follows:
											Components of Changes in
											Accumulated Other
											Comprehensive Income (after tax)
	(millions)	Pretax total			Total tax			After tax total			Total net			Net			Foreign
		accumulated			(provision)			accumulated			unrealized			unrealized			currency
		other			benefit			other			gains (losses)			gains on			translation
		comprehensive						comprehensive			on securities			forecasted			adjustment
		income						income						transactions
	Balance at December 31, 2013	$	1,464.10		$	(512.4	)	$	951.7		$	947		$	4.1		$	0.6
	Other comprehensive income (loss) before reclassifications:
	Investment securities	362.1			(126.7		)	235.4			235.4			0			0
	Net non-credit related OTTI losses, adjusted for valuation changes	0			0			0			0			0			0
	Forecasted transactions	(1.6		)	0.6			(1.0		)	0			(1.0		)	0
	Foreign currency translation adjustment	(1.3		)	0.4			(0.9		)	0			0			(0.9		)
	Total other comprehensive income (loss) before reclassifications	359.2			(125.7		)	233.5			235.4			(1.0		)	(0.9		)
	Less: Reclassification adjustment for amounts realized in net income by income statement line item:
	Net impairment losses recognized in earnings	(7.7		)	2.7			(5.0		)	(5.0		)	0			0
	Net realized gains (losses) on securities	255			(89.2		)	165.8			165.5			0.3			0
	Interest expense	2			(0.7		)	1.3			0			1.3			0
	Total reclassification adjustment for amounts realized in net income	249.3			(87.2		)	162.1			160.5			1.6			0
	Total other comprehensive income (loss)	109.9			(38.5		)	71.4			74.9			(2.6		)	(0.9		)
	Balance at December 31, 2014	$	1,574.00		$	(550.9	)	$	1,023.10		$	1,021.90		$	1.5		$	(0.3	)
											Components of Changes in
											Accumulated Other
											Comprehensive Income (after tax)
	(millions)	Pretax total			Total tax			After tax total			Total net			Net			Foreign
		accumulated			(provision)			accumulated			unrealized			unrealized			currency
		other			benefit			other			gains (losses)			gains on			translation
		comprehensive						comprehensive			on securities			forecasted			adjustment
		income						income						transactions
	Balance at December 31, 2012	$	1,340.00		$	(469.0	)	$	871		$	862.7		$	6.1		$	2.2
	Other comprehensive income (loss) before reclassifications:
	Investment securities	368.2			(128.9		)	239.3			239.3			0			0
	Net non-credit related OTTI losses, adjusted for valuation changes	0.4			(0.1		)	0.3			0.3			0			0
	Forecasted transactions	0			0			0			0			0			0
	Foreign currency translation adjustment	(2.5		)	0.9			(1.6		)	0			0			(1.6		)
	Total other comprehensive income (loss) before reclassifications	366.1			(128.1		)	238			239.6			0			(1.6		)
	Less: Reclassification adjustment for amounts realized in net income by income statement line item:
	Net impairment losses recognized in earnings	(5.7		)	2			(3.7		)	(3.7		)	0			0
	Net realized gains (losses) on securities	245.5			(86.0		)	159.5			159			0.5			0
	Interest expense	2.2			(0.7		)	1.5			0			1.5			0
	Total reclassification adjustment for amounts realized in net income	242			(84.7		)	157.3			155.3			2			0
	Total other comprehensive income (loss)	124.1			(43.4		)	80.7			84.3			(2.0		)	(1.6		)
	Balance at December 31, 2013	$	1,464.10		$	(512.4	)	$	951.7		$	947		$	4.1		$	0.6
											Components of Changes in
											Accumulated Other
											Comprehensive Income (after tax)
	(millions)	Pretax total			Total tax			After tax total			Total net			Net			Foreign
		accumulated			(provision)			accumulated			unrealized			unrealized			currency
		other			benefit			other			gains (losses)			gains on			translation
		comprehensive						comprehensive			on securities			forecasted			adjustment
		income						income						transactions
	Balance at December 31, 2011	$	1,065.40		$	(372.9	)	$	692.5		$	682.8		$	7.9		$	1.8
	Other comprehensive income (loss) before reclassifications:
	Investment securities	488			(170.8		)	317.2			317.2			0			0
	Net non-credit related OTTI losses, adjusted for valuation changes	7.9			(2.8		)	5.1			5.1			0			0
	Forecasted transactions	0			0			0			0			0			0
	Foreign currency translation adjustment	0.6			(0.2		)	0.4			0			0			0.4
	Total other comprehensive income (loss) before reclassifications	496.5			(173.8		)	322.7			322.3			0			0.4
	Less: Reclassification adjustment for amounts realized in net income by income statement line item:
	Net impairment losses recognized in earnings	(0.4		)	0.1			(0.3		)	(0.3		)	0			0
	Net realized gains (losses) on securities	220.1			(77.0		)	143.1			142.7			0.4			0
	Interest expense	2.2			(0.8		)	1.4			0			1.4			0
Total reclassification adjustment for amounts realized in net income	221.9			(77.7		)	144.2			142.4			1.8			0
Total other comprehensive income (loss)	274.6			(96.1		)	178.5			179.9			(1.8		)	0.4
Balance at December 31, 2012	$	1,340.00		$	(469.0	)	$	871		$	862.7		$	6.1		$	2.2

Commitments_and_Contingencies_

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
Minimum Commitments under Noncancelable Operating Lease Agreements	The minimum commitments under these agreements at December 31, 2014, were as follows:
	(millions)	Commitments
	2015	$	46.2
	2016	43.7
	2017	37.2
	2018	27.1
	2019	16.4
	Thereafter	4.4
	Total	$	175
Expense Incurred for Leases	The expense we incurred for the leases disclosed above, as well as other operating leases that may be cancelable or have terms less than one year, was:
	(millions)	Expense
	2014	$	63.4
	2013	64.6
	2012	71.9

Dividends_Tables

Dividends (Tables)	12 Months Ended
	Dec. 31, 2014
Dividends [Abstract]
Dividends	Following is a summary of our shareholder dividends, both variable and special, that were paid in the last three years:
	(millions, except per share amounts)			Amount
	Dividend Type	Declared	Paid	Per		Total1
				Share
	Annual – Variable	Dec-14	Feb-15	$	0.6862	$	404.1
	Annual – Variable	Dec-13	Feb-14	0.4929		293.9
	Special	Dec-13	Feb-14	1		596.3
	Annual – Variable	Dec-12	Feb-13	0.2845		172
	Special	Oct-12	Nov-12	1		604.7
	1 Based on shares outstanding as of the record date.

SCHEDULE_I_Summary_Of_Investme1

SCHEDULE I - Summary Of Investments - Other Than Investments in Related Parties Summary Of Investments - Other than Investments In Related Parties (Detail) (USD $)	Dec. 31, 2014
In Millions, unless otherwise specified
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	$17,402.80
Fair Value	19,018
Amount At Which Shown In The Balance Sheet	19,018
Fixed maturities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	13,374.20
Fair Value	13,549.20
Amount At Which Shown In The Balance Sheet	13,549.20
Fixed maturities | Bonds | US Government and Government Agencies and Authorities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	2,641.10
Fair Value	2,667.10
Amount At Which Shown In The Balance Sheet	2,667.10
Fixed maturities | Bonds | State and local government obligations
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	2,095.70
Fair Value	2,139.20
Amount At Which Shown In The Balance Sheet	2,139.20
Fixed maturities | Bonds | Foreign government obligations
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	14.2
Fair Value	14.2
Amount At Which Shown In The Balance Sheet	14.2
Fixed maturities | Bonds | Public Utility, Bonds
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	63.1
Fair Value	66.6
Amount At Which Shown In The Balance Sheet	66.6
Fixed maturities | Bonds | Corporate And Other Debt Securities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	2,750.80
Fair Value	2,770.10
Amount At Which Shown In The Balance Sheet	2,770.10
Fixed maturities | Bonds | Asset-backed Securities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	5,549.10
Fair Value	5,612.80
Amount At Which Shown In The Balance Sheet	5,612.80
Fixed maturities | Redeemable preferred stocks
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	260.2
Fair Value	279.2
Amount At Which Shown In The Balance Sheet	279.2
Equity securities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	1,879.60
Fair Value	3,319.80
Amount At Which Shown In The Balance Sheet	3,319.80
Equity securities | Common Stocks, by Industry | Utilities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	95
Fair Value	143.3
Amount At Which Shown In The Balance Sheet	143.3
Equity securities | Common Stocks, by Industry | Financials
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	220.1
Fair Value	438.4
Amount At Which Shown In The Balance Sheet	438.4
Equity securities | Common Stocks, by Industry | Industrials
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	974.1
Fair Value	1,910.60
Amount At Which Shown In The Balance Sheet	1,910.60
Equity securities | Nonredeemable preferred stocks
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	590.4
Fair Value	827.5
Amount At Which Shown In The Balance Sheet	827.5
Short-term investments
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	2,149	[1]
Fair Value	2,149	[1]
Amount At Which Shown In The Balance Sheet	$2,149	[1]
[1]	Includes $5.7 million in treasury bills issued by the Australian government.

SCHEDULE_I_Summary_Of_Investme2

SCHEDULE I - Summary Of Investments - Other Than Investments in Related Parties Summary Of Investments - Other than Investments In Related Parties (Parenthetical) (Detail) (USD $)	Dec. 31, 2014
In Millions, unless otherwise specified
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	$17,402.80
Fair Value	19,018
Amount At Which Shown In The Balance Sheet	19,018
Short-term investments
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	2,149	[1]
Fair Value	2,149	[1]
Amount At Which Shown In The Balance Sheet	2,149	[1]
Short-term investments | Foreign Government Debt
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	5.7
Fair Value	5.7
Amount At Which Shown In The Balance Sheet	$5.70
[1]	Includes $5.7 million in treasury bills issued by the Australian government.

SCHEDULE_II_Condensed_Financia1

SCHEDULE II - Condensed Financial Information Of Registrant Condensed Statements Of Comprehensive Income (Parent Company) (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Revenues
Gains (losses) on extinguishment of debt	($4.80)		($4.30)		($1.80)
Total revenues	19,391.40		18,170.90		17,083.90
Expenses
Interest expense	116.9		118.2		123.8
Total expenses	17,484		16,450.90		15,766.20
Income before income taxes	1,907.40		1,720		1,317.70
Provision (benefit) for income taxes	626.4		554.6		415.4
Net income	1,281		1,165.40		902.3
Other comprehensive income (loss)	71.4		80.7		178.5
Comprehensive income	1,352.40		1,246.10		1,080.80
Parent Company
Revenues
Dividends from subsidiaries	1,000.20		1,119.70		782.3
Undistributed income (loss) from subsidiaries	358.3		117.5		193.1
Equity in net income of subsidiaries	1,358.50	[1]	1,237.20	[1]	975.4	[1]
Intercompany investment income	2.4	[1]	2.8	[1]	6.1	[1]
Gains (losses) on extinguishment of debt	-4.8		-4.3		-1.8
Other Income	0	[2]	2.6	[2]	0	[2]
Total revenues	1,356.10		1,238.30		979.7
Expenses
Interest expense	120.2		121.2		126.3
Deferred compensation	2.8	[3]	9.5	[3]	5.5	[3]
Other operating costs and expenses	4.4		4		3.7
Total expenses	127.4		134.7		135.5
Income before income taxes	1,228.70		1,103.60		844.2
Provision (benefit) for income taxes	-52.3		-61.8		-58.1
Net income	1,281		1,165.40		902.3
Other comprehensive income (loss)	71.4		80.7		178.5
Comprehensive income	$1,352.40		$1,246.10		$1,080.80
[1]	Eliminated in consolidation.
[2]	Represents gain on net death benefit received on life insurance policies.
[3]	See Note 4 – Employee Benefit Plans in these condensed financial statements.

SCHEDULE_II_Condensed_Financia2

SCHEDULE II - Condensed Financial Information Of Registrant Condensed Balance Sheets (Parent Company) (Detail) (USD $)	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012	Dec. 31, 2011
In Millions, unless otherwise specified
Assets
Other assets	$301.40		$304.30
Total assets	25,787.60		24,408.20
Liabilities and Shareholders' Equity
Accounts payable, accrued expenses, and other liabilities	1,893.80	[1]	1,785	[1]
Dividend payable	404.1		890.2
Debt	2,164.70	[2]	1,860.90	[2]
Total liabilities	18,859		18,218.70
Common shares, $1.00 par value (authorized 900.0; issued 797.6, including treasury shares of 209.8 and 201.8)	587.8		595.8
Paid-in capital	1,184.30		1,142
Retained earnings	4,133.40		3,500
Total accumulated other comprehensive income	1,023.10		951.7		871	692.5
Total shareholders' equity	6,928.60		6,189.50		6,007
Total liabilities and shareholders' equity	25,787.60		24,408.20
Parent Company
Assets
Investment in affiliate	5		5
Investment in subsidiaries	7,423.50	[3]	6,923.50	[3]
Receivable from investment subsidiary	1,677.50	[3]	1,648.40	[3]
Intercompany receivable	413	[3]	307.6	[3]
Net deferred income taxes	74.5		69.1
Other assets	123.9		141.8
Total assets	9,717.40		9,095.40
Liabilities and Shareholders' Equity
Accounts payable, accrued expenses, and other liabilities	220		154.8
Dividend payable	404.1		890.2
Debt	2,164.70		1,860.90
Total liabilities	2,788.80		2,905.90
Common shares, $1.00 par value (authorized 900.0; issued 797.6, including treasury shares of 209.8 and 201.8)	587.8		595.8
Paid-in capital	1,184.30		1,142
Retained earnings	4,133.40		3,500
Total accumulated other comprehensive income	1,023.10		951.7
Total shareholders' equity	6,928.60		6,189.50
Total liabilities and shareholders' equity	$9,717.40		$9,095.40
[1]	See Note 12 – Litigation and Note 13 – Commitments and Contingencies for further discussion.
[2]	Consists of long-term debt. See Note 4 – Debt for further discussion.
[3]	Eliminated in consolidation.

SCHEDULE_II_Condensed_Financia3

SCHEDULE II - Condensed Financial Information Of Registrant Condensed Balance Sheets (Parent Company) (Parenthetical) (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, except Per Share data, unless otherwise specified
Condensed Financial Statements, Captions [Line Items]
Common Shares, par value (USD per share)	$1	$1
Common Shares, authorized (shares)	900	900
Common Shares, issued (shares)	797.6	797.6
Common Shares, treasury shares (shares)	209.8	201.8
Parent Company
Condensed Financial Statements, Captions [Line Items]
Common Shares, par value (USD per share)	$1	$1
Common Shares, authorized (shares)	900	900
Common Shares, issued (shares)	797.6	797.6
Common Shares, treasury shares (shares)	209.8	201.8

SCHEDULE_II_Condensed_Financia4

SCHEDULE II - Condensed Financial Information Of Registrant Condensed Statements Of Cash Flows (Parent Company) (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash Flows From Operating Activities:
Net income	$1,281,000,000	$1,165,400,000	$902,300,000
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of equity-based compensation	51,400,000	64,900,000	63,400,000
(Gains) losses on extinguishment of debt	4,800,000	4,300,000	1,800,000
Changes in:
Accounts payable, accrued expenses, and other liabilities	92,000,000	165,000,000	123,600,000
Income taxes	97,500,000	57,800,000	19,800,000
Other, net	-13,200,000	-28,100,000	-10,400,000
Net cash provided by operating activities	1,725,600,000	1,899,900,000	1,691,400,000
Cash Flows From Investing Activities:
Net cash provided by (used in) investing activities	-836,900,000	-1,356,500,000	-264,900,000
Cash Flows From Financing Activities:
Proceeds from exercise of stock options	0	0	500,000
Tax benefit from exercise/vesting of equity-based compensation	12,800,000	10,300,000	5,800,000
Net proceeds from debt issuance	344,700,000	0	0
Payment of debt	0	-150,000,000	-350,000,000
Reacquisition of debt	-48,900,000	-58,100,000	-32,500,000
Acquisition of treasury shares	-271,400,000	-273,400,000	-174,200,000
Net cash used in financing activities	-855,400,000	-646,800,000	-1,404,100,000
Increase (decrease) in cash	33,300,000	-104,000,000	23,400,000
Cash, Beginning of year	75,100,000	179,100,000	155,700,000
Cash, End of year	108,400,000	75,100,000	179,100,000
Parent Company
Cash Flows From Operating Activities:
Net income	1,281,000,000	1,165,400,000	902,300,000
Adjustments to reconcile net income to net cash provided by operating activities:
Undistributed (income) loss from subsidiaries	-358,300,000	-117,500,000	-193,100,000
Amortization of equity-based compensation	2,200,000	2,100,000	2,000,000
(Gains) losses on extinguishment of debt	4,800,000	4,300,000	1,800,000
Changes in:
Intercompany receivable	-105,400,000	-11,400,000	-58,600,000
Accounts payable, accrued expenses, and other liabilities	18,200,000	19,400,000	300,000
Income taxes	61,100,000	-55,800,000	21,700,000
Other, net	400,000	-16,300,000	-9,900,000
Net cash provided by operating activities	904,000,000	990,200,000	666,500,000
Cash Flows From Investing Activities:
Additional investments in equity securities of consolidated subsidiaries	-21,100,000	-13,900,000	-36,100,000
Investment in affiliate	0	-4,000,000	0
(Paid to) received from investment subsidiary	-29,100,000	-325,500,000	773,700,000
Net cash provided by (used in) investing activities	-50,200,000	-343,400,000	737,600,000
Cash Flows From Financing Activities:
Proceeds from exercise of stock options	0	0	500,000
Tax benefit from exercise/vesting of equity-based compensation	12,800,000	10,300,000	5,800,000
Net proceeds from debt issuance	346,300,000	0	0
Payment of debt	0	-150,000,000	-350,000,000
Reacquisition of debt	-48,900,000	-58,100,000	-32,500,000
Dividends paid to shareholders	-892,600,000	-175,600,000	-853,700,000
Acquisition of treasury shares	-271,400,000	-273,400,000	-174,200,000
Net cash used in financing activities	-853,800,000	-646,800,000	-1,404,100,000
Increase (decrease) in cash	0	0	0
Cash, Beginning of year	0	0	0
Cash, End of year	$0	$0	$0

SCHEDULE_II_Condensed_Financia5

SCHEDULE II - Condensed Financial Information Of Registrant Condensed Financial Information Of Registrant - Additional Information (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Billions, unless otherwise specified
Disclosure Condensed Financial Information Of Registrant Additional Information [Abstract]
Securities Held in Consolidated Non-Insurance Subsidiary	$1.90	$1.80

SCHEDULE_II_Condensed_Financia6

SCHEDULE II - Condensed Financial Information Of Registrant Progressive Corporation Cash Paid (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Disclosure Progressive Corporation Cash Paid [Abstract]
Income Taxes	$515	$497	$389.10
Interest	$116	$122.30	$135

SCHEDULE_III_Supplementary_Ins1

SCHEDULE III - Supplementary Insurance Information Supplementary Insurance Information (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Supplementary Insurance Information, by Segment [Line Items]
Deferred policy acquisition costs	$457.20	[1]	$447.60	[1]	$434.50	[1]
Future policy benefits, losses, claims, and loss expenses	8,857.40	[1]	8,479.70	[1]	7,838.40	[1]
Unearned premiums	5,440.10	[1]	5,174.50	[1]	4,930.70	[1]
Other policy claims and benefits payable	0	[1]	0	[1]	0	[1]
Premium revenue	18,398.50		17,103.40		16,018
Net investment income	389.5	[1],[2]	403.2	[1],[2]	427.6	[1],[2]
Benefits, claims, losses, and settlement expenses	13,306.20		12,472.40		11,948
Amortization of deferred policy acquisition costs	1,524		1,451.80		1,436.60
Other operating expenses	2,467.10		2,350.90		2,206.30
Net premiums written	18,654.60		17,339.70		16,372.70
Personal Lines
Supplementary Insurance Information, by Segment [Line Items]
Premium revenue	16,561		15,341.60		14,368.10
Benefits, claims, losses, and settlement expenses	12,161.20		11,194.60		10,745.30
Amortization of deferred policy acquisition costs	1,322.90		1,257.50		1,250.40
Other operating expenses	2,262.60		2,149.20		2,010.50
Net premiums written	16,759.20		15,569.20		14,636.80
Commercial Lines
Supplementary Insurance Information, by Segment [Line Items]
Premium revenue	1,837.50		1,761.60		1,649
Benefits, claims, losses, and settlement expenses	1,133.40		1,267.30		1,196.60
Amortization of deferred policy acquisition costs	201.1		194.3		186.2
Other operating expenses	204.2		201.2		195.2
Net premiums written	1,895.40		1,770.50		1,735.90
Other Indemnity
Supplementary Insurance Information, by Segment [Line Items]
Premium revenue	0		0.2		0.9
Benefits, claims, losses, and settlement expenses	11.6		10.5		6.1
Amortization of deferred policy acquisition costs	0		0		0
Other operating expenses	0.3		0.5		0.6
Net premiums written	$0		$0		$0
[1]	Progressive does not allocate assets, liabilities, or investment income to operating segments.
[2]	Excludes total net realized gains (losses) on securities.

SCHEDULE_IV_Reinsurance_Reinsu

SCHEDULE IV - Reinsurance Reinsurance (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Gross Amount	$18,648,400,000	$17,317,900,000	$16,207,600,000
Ceded to Other Companies	249,900,000	214,500,000	189,600,000
Property, Liability and Casualty Insurance Segment
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Gross Amount	18,648,400,000	17,317,900,000	16,207,600,000
Ceded to Other Companies	249,900,000	214,500,000	189,600,000
Assumed From Other Companies	0	0	0
Net Amount	$18,398,500,000	$17,103,400,000	$16,018,000,000
Percentage of Amount Assumed to Net	0.00%	0.00%	0.00%

SCHEDULE_VISupplemental_Inform1

SCHEDULE VI-Supplemental Information Concerning Property - Casualty Insurance Operations Supplemental Information Concerning Property - Casualty Insurance Operations (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Disclosure Supplemental Information Concerning Property Casualty Insurance Operations [Abstract]
Losses and Loss Adjustment Expenses Incurred Related to Current Year	$13,330.30	$12,427.30	$11,926
Losses and Loss Adjustment Expenses Incurred Related to Prior Years	-24.1	45.1	22
Paid Losses and Loss Adjustment Expenses	$13,068.50	$12,014.90	$11,431.80

Reporting_And_Accounting_Polic3

Reporting And Accounting Policies Advertising Costs (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Marketing and Advertising Expense [Abstract]
Advertising Expense	$681.80	$619.30	$546.80

Reporting_And_Accounting_Polic4

Reporting And Accounting Policies Interest Capitalized (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Disclosure Interest Capitalized [Abstract]
Capitalized Interest	$1.30	$0.80	$0.30

Reporting_And_Accounting_Polic5

Reporting And Accounting Policies Equity Based Compensation (Detail) (Stock Compensation Plan, USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Stock Compensation Plan
Incentive Compensation Plans Expense [Line Items]
Pretax expense	$51.40	$64.90	$63.40
Tax benefit	$18	$22.70	$22.20

Reporting_And_Accounting_Polic6

Reporting And Accounting Policies Supplemental Cash Flow Information (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Disclosure Supplemental Cash Flow Information [Abstract]
Income Taxes	$515	$497	$389.10
Interest	$116	$122.30	$135

Reporting_And_Accounting_Polic7

Reporting And Accounting Policies - Additional Information (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Significant Accounting Policies [Line Items]
Number of Subsidiaries	53
Number of Mutual Insurance Company Affiliates	1
Number of Limited Partnership Investment Affiliates	1
Number of Properties Held for Sale	1
Assets Held-for-Sale, Property, Plant and Equipment	8.7
Lower Limit
Significant Accounting Policies [Line Items]
Auction Rate Securities, Period Between Auction Dates	7 days
Upper Limit
Significant Accounting Policies [Line Items]
Auction Rate Securities, Period Between Auction Dates	49 days
computer equipment and laptop computers
Significant Accounting Policies [Line Items]
Estimated useful lives	3 years
Building, Building Improvements, and Integrated Components | Lower Limit
Significant Accounting Policies [Line Items]
Estimated useful lives	7 years
Building, Building Improvements, and Integrated Components | Upper Limit
Significant Accounting Policies [Line Items]
Estimated useful lives	40 years
Property, Plant and Equipment, Other Types | Lower Limit
Significant Accounting Policies [Line Items]
Estimated useful lives	3 years
Property, Plant and Equipment, Other Types | Upper Limit
Significant Accounting Policies [Line Items]
Estimated useful lives	15 years
Land and Building
Significant Accounting Policies [Line Items]
Land and buildings as a percentage of total property and equipment	77.00%	76.00%

Investments_Investment_Portfol

Investments Investment Portfolio by Major Security Type (Detail) (USD $)	Dec. 31, 2014		Dec. 31, 2013
In Millions, unless otherwise specified
Schedule of Available-for-sale Securities [Line Items]
Cost	$17,402.80	[1],[2]	$16,584.70	[1],[2]
Gross Unrealized Gains	1,621.40	[1],[2]	1,582.90	[1],[2]
Gross Unrealized Losses	-49.2	[1],[2]	-126	[1],[2]
Net Realized Gains (Losses)	43	[1],[2],[3]	13.1	[1],[2],[3]
Total investments at fair value	19,018	[1],[2]	18,054.70	[1],[2]
% of Total Fair Value	100.00%	[1],[2]	100.00%	[1],[2]
Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost	13,374.20		13,415.30
Gross Unrealized Gains	207.1		242.4
Gross Unrealized Losses	-32.7		-119.1
Net Realized Gains (Losses)	0.6	[3]	1.8	[3]
Total investments at fair value	13,549.20		13,540.40
% of Total Fair Value	71.20%		75.00%
Fixed maturities | U.S. government obligations
Schedule of Available-for-sale Securities [Line Items]
Cost	2,641.10		3,630.40
Gross Unrealized Gains	27.3		48.4
Gross Unrealized Losses	-1.3		-16.6
Net Realized Gains (Losses)	0	[3]	0	[3]
Total investments at fair value	2,667.10		3,662.20
% of Total Fair Value	14.00%		20.30%
Fixed maturities | State and local government obligations
Schedule of Available-for-sale Securities [Line Items]
Cost	2,095.70		2,247.30
Gross Unrealized Gains	44.6		27.1
Gross Unrealized Losses	-1.1		-18.4
Net Realized Gains (Losses)	0	[3]	0	[3]
Total investments at fair value	2,139.20		2,256
% of Total Fair Value	11.20%		12.50%
Fixed maturities | Foreign government obligations
Schedule of Available-for-sale Securities [Line Items]
Cost	14.2		15.6
Gross Unrealized Gains	0		0
Gross Unrealized Losses	0		0
Net Realized Gains (Losses)	0	[3]	0	[3]
Total investments at fair value	14.2		15.6
% of Total Fair Value	0.10%		0.10%
Fixed maturities | Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Cost	2,813.90		2,885
Gross Unrealized Gains	32.9		60.4
Gross Unrealized Losses	-10.4		-20.4
Net Realized Gains (Losses)	0.3	[3]	1.6	[3]
Total investments at fair value	2,836.70		2,926.60
% of Total Fair Value	14.90%		16.20%
Fixed maturities | Residential mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Cost	1,635.50		1,110.10
Gross Unrealized Gains	34.5		31.9
Gross Unrealized Losses	-10.8		-14.1
Net Realized Gains (Losses)	-0.7	[3]	0	[3]
Total investments at fair value	1,658.50		1,127.90
% of Total Fair Value	8.70%		6.20%
Fixed maturities | Commercial mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Cost	2,278.70		2,154.40
Gross Unrealized Gains	39.3		43.9
Gross Unrealized Losses	-2.6		-37.8
Net Realized Gains (Losses)	0.2	[3]	0	[3]
Total investments at fair value	2,315.60		2,160.50
% of Total Fair Value	12.20%		12.00%
Fixed maturities | Other asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Cost	1,634.90		1,073
Gross Unrealized Gains	3.8		6.6
Gross Unrealized Losses	-0.8		-2.1
Net Realized Gains (Losses)	0.8	[3]	0.2	[3]
Total investments at fair value	1,638.70		1,077.70
% of Total Fair Value	8.60%		6.00%
Fixed maturities | Redeemable preferred stocks
Schedule of Available-for-sale Securities [Line Items]
Cost	260.2		299.5
Gross Unrealized Gains	24.7		24.1
Gross Unrealized Losses	-5.7		-9.7
Net Realized Gains (Losses)	0	[3]	0	[3]
Total investments at fair value	279.2		313.9
% of Total Fair Value	1.50%		1.70%
Equity securities | Nonredeemable preferred stocks
Schedule of Available-for-sale Securities [Line Items]
Cost	590.4		445.7
Gross Unrealized Gains	201.1		258.7
Gross Unrealized Losses	-6.4		-4.5
Net Realized Gains (Losses)	42.4	[3]	11.3	[3]
Total investments at fair value	827.5		711.2
% of Total Fair Value	4.40%		3.90%
Equity securities | Common equities
Schedule of Available-for-sale Securities [Line Items]
Cost	1,289.20		1,451.10
Gross Unrealized Gains	1,213.20		1,081.80
Gross Unrealized Losses	-10.1		-2.4
Net Realized Gains (Losses)	0	[3]	0	[3]
Total investments at fair value	2,492.30		2,530.50
% of Total Fair Value	13.10%		14.00%
Short-term investments
Schedule of Available-for-sale Securities [Line Items]
Cost	2,149		1,272.60
Gross Unrealized Gains	0		0
Gross Unrealized Losses	0		0
Net Realized Gains (Losses)	0	[3]	0	[3]
Total investments at fair value	$2,149		$1,272.60
% of Total Fair Value	11.30%		7.10%
[1]	The total fair value of the portfolio included $1.9 billion and $1.8 billion at December 31, 2014 and 2013, respectively, of securities held in a consolidated, non-insurance subsidiary of the holding company, net of any unsettled security transactions.
[2]	Our portfolio reflects the effect of unsettled security transactions and collateral on open derivative positions; at December 31, 2014, $31.3 million was included in "other liabilities," compared to $61.3 million at December 31, 2013.
[3]	Represents net holding period gains (losses) on certain hybrid securities (discussed below).

Investments_Investment_Portfol1

Investments Investment Portfolio by Major Security Type (Parenthetical) (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Investments, Debt and Equity Securities [Abstract]
Net unsettled security transactions offset in other liabilities	$31,300,000	$61,300,000
Securities in the portfolio of a consolidated, non-insurance subsidiary of the holding company, net of any unsettled security transactions	$1,900,000,000	$1,800,000,000

Investments_Hybrid_Securities_

Investments Hybrid Securities (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Hybrid Securities [Line Items]
Hybrid securities	$427.70	$239.30
Fixed maturities
Hybrid Securities [Line Items]
Hybrid securities	305.4	179
Fixed maturities | Corporate debt securities
Hybrid Securities [Line Items]
Hybrid securities	139.8	164.2
Fixed maturities | Residential mortgage-backed securities
Hybrid Securities [Line Items]
Hybrid securities	120.7	0
Fixed maturities | Commercial mortgage-backed securities
Hybrid Securities [Line Items]
Hybrid securities	31.2	0
Fixed maturities | Other asset-backed securities
Hybrid Securities [Line Items]
Hybrid securities	13.7	14.8
Equity securities | Nonredeemable preferred stocks
Hybrid Securities [Line Items]
Hybrid securities	$122.30	$60.30

Investments_Composition_of_Fix

Investments Composition of Fixed Maturities by Maturity (Detail) (USD $)	Dec. 31, 2014
In Millions, unless otherwise specified
Available for sale, cost
Less than one year	$3,180.10
One to five years	7,026.30
Five to ten years	3,093
Ten years or greater	59
Total	13,358.40	[1]
Available for sale, Fair value
Less than one year	3,217.40
One to five years	7,097.20
Five to ten years	3,152.90
Ten years or greater	65.9
Total	$13,533.40	[1]
[1]	Excludes $15.8 million related to our open interest rate swap positions.

Investments_Composition_of_Fix1

Investments Composition of Fixed Maturities by Maturity (Parenthetical) (Details) (USD $)	Dec. 31, 2014		Dec. 31, 2013
In Millions, unless otherwise specified
Schedule of Available-for-sale Securities [Line Items]
Open interest rate swap positions	$15.80	[1]	$68.10	[1]
Interest Rate Swaps
Schedule of Available-for-sale Securities [Line Items]
Open interest rate swap positions	$15.80
[1]	To the extent we hold both derivative assets and liabilities with the same counterparty that are subject to an enforceable master netting arrangement, we expect that we will report them on a gross basis on our balance sheets, consistent with our historical presentation.

Investments_Gross_Unrealized_l

Investments Gross Unrealized losses by Major Security (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Investments, Unrealized Loss Position [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	318	423
Total Fair Value	$4,217.80	$5,723.40
Gross Unrealized Losses	-49.2	-126
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	230	346
Less than 12 Months Fair Value	3,062.50	4,865.90
Less than 12 Months Unrealized Losses	-26.2	-87.5
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	88	77
12 Months or Greater Fair Value	1,155.30	857.5
12 Months or Greater Unrealized Losses	-23	-38.5
Fixed maturities
Investments, Unrealized Loss Position [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	290	392
Total Fair Value	3,918	5,521.40
Gross Unrealized Losses	-32.7	-119.1
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	206	319
Less than 12 Months Fair Value	2,857.50	4,665.10
Less than 12 Months Unrealized Losses	-13	-80.6
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	84	73
12 Months or Greater Fair Value	1,060.50	856.3
12 Months or Greater Unrealized Losses	-19.7	-38.5
Fixed maturities | U.S. government obligations
Investments, Unrealized Loss Position [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	11	29
Total Fair Value	428.2	1,444.30
Gross Unrealized Losses	-1.3	-16.6
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	5	28
Less than 12 Months Fair Value	150.7	1,434.60
Less than 12 Months Unrealized Losses	-0.3	-16.3
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	6	1
12 Months or Greater Fair Value	277.5	9.7
12 Months or Greater Unrealized Losses	-1	-0.3
Fixed maturities | State and local government obligations
Investments, Unrealized Loss Position [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	46	141
Total Fair Value	234.2	844.2
Gross Unrealized Losses	-1.1	-18.4
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	28	119
Less than 12 Months Fair Value	177.9	759.3
Less than 12 Months Unrealized Losses	-0.4	-17.1
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	18	22
12 Months or Greater Fair Value	56.3	84.9
12 Months or Greater Unrealized Losses	-0.7	-1.3
Fixed maturities | Corporate debt securities
Investments, Unrealized Loss Position [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	53	51
Total Fair Value	843.2	997.6
Gross Unrealized Losses	-10.4	-20.4
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	43	45
Less than 12 Months Fair Value	647.5	831.1
Less than 12 Months Unrealized Losses	-6.1	-17.8
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	10	6
12 Months or Greater Fair Value	195.7	166.5
12 Months or Greater Unrealized Losses	-4.3	-2.6
Fixed maturities | Residential mortgage-backed securities
Investments, Unrealized Loss Position [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	70	66
Total Fair Value	844.2	763.5
Gross Unrealized Losses	-10.8	-14.1
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	33	45
Less than 12 Months Fair Value	465.2	597.6
Less than 12 Months Unrealized Losses	-3.1	-7.9
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	37	21
12 Months or Greater Fair Value	379	165.9
12 Months or Greater Unrealized Losses	-7.7	-6.2
Fixed maturities | Commercial mortgage-backed securities
Investments, Unrealized Loss Position [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	63	76
Total Fair Value	723.4	1,061.90
Gross Unrealized Losses	-2.6	-37.8
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	54	60
Less than 12 Months Fair Value	667.5	809.2
Less than 12 Months Unrealized Losses	-1.4	-19.7
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	9	16
12 Months or Greater Fair Value	55.9	252.7
12 Months or Greater Unrealized Losses	-1.2	-18.1
Fixed maturities | Other asset-backed securities
Investments, Unrealized Loss Position [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	44	25
Total Fair Value	741.8	287.2
Gross Unrealized Losses	-0.8	-2.1
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	42	22
Less than 12 Months Fair Value	715.7	233.3
Less than 12 Months Unrealized Losses	-0.7	-1.8
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	2	3
12 Months or Greater Fair Value	26.1	53.9
12 Months or Greater Unrealized Losses	-0.1	-0.3
Fixed maturities | Redeemable preferred stocks
Investments, Unrealized Loss Position [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	3	4
Total Fair Value	103	122.7
Gross Unrealized Losses	-5.7	-9.7
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	1	0
Less than 12 Months Fair Value	33	0
Less than 12 Months Unrealized Losses	-1	0
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	2	4
12 Months or Greater Fair Value	70	122.7
12 Months or Greater Unrealized Losses	-4.7	-9.7
Equity securities
Investments, Unrealized Loss Position [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	28	31
Total Fair Value	299.8	202
Gross Unrealized Losses	-16.5	-6.9
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	24	27
Less than 12 Months Fair Value	205	200.8
Less than 12 Months Unrealized Losses	-13.2	-6.9
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	4	4
12 Months or Greater Fair Value	94.8	1.2
12 Months or Greater Unrealized Losses	-3.3	0
Equity securities | Nonredeemable preferred stocks
Investments, Unrealized Loss Position [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	8	7
Total Fair Value	231.4	142.3
Gross Unrealized Losses	-6.4	-4.5
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	5	7
Less than 12 Months Fair Value	143.2	142.3
Less than 12 Months Unrealized Losses	-3.6	-4.5
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	3	0
12 Months or Greater Fair Value	88.2	0
12 Months or Greater Unrealized Losses	-2.8	0
Equity securities | Common equities
Investments, Unrealized Loss Position [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	20	24
Total Fair Value	68.4	59.7
Gross Unrealized Losses	-10.1	-2.4
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	19	20
Less than 12 Months Fair Value	61.8	58.5
Less than 12 Months Unrealized Losses	-9.6	-2.4
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	1	4
12 Months or Greater Fair Value	6.6	1.2
12 Months or Greater Unrealized Losses	($0.50)	$0

Investments_Total_NonCredit_Po

Investments Total Non-Credit Portion of Other-Than-Temporary Impairment Recorded in Accumulated Other Comprehensive Income, Reflecting Original Non-Credit Loss at Time Credit Impairment (Detail) (Fixed maturities, USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Other Than Temporary Impairment Non Credit Losses Recognized In Accumulated Other Comprehensive Income [Line Items]
Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Pre-Tax, Available-for-sale, Debt Securities	($44.70)	($45)
Residential mortgage-backed securities
Other Than Temporary Impairment Non Credit Losses Recognized In Accumulated Other Comprehensive Income [Line Items]
Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Pre-Tax, Available-for-sale, Debt Securities	-44.1	-44.1
Commercial mortgage-backed securities
Other Than Temporary Impairment Non Credit Losses Recognized In Accumulated Other Comprehensive Income [Line Items]
Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Pre-Tax, Available-for-sale, Debt Securities	($0.60)	($0.90)

Investments_OTTI_Credit_Losses

Investments OTTI Credit Losses Recognized in Earnings (Detail) (Fixed maturities, USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Beginning balance	$19.60		$27.70		$35.80
Credit losses for which an OTTI was previously recognized	0		0.1		0.1
Credit losses for which an OTTI was not previously recognized	0		0		0.3
Reductions for securities sold/matured	-0.1		0		-0.2
Change in recoveries of future cash flows expected to be collected	-6.4	[1],[2]	-8	[1],[2]	-4	[1],[2]
Reductions for previously recognized credit impairments written-down to fair value	0	[3]	-0.2	[3]	-4.3	[3]
Ending balance	13.1		19.6		27.7
Residential mortgage-backed securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Beginning balance	19.2		27.1		34.5
Credit losses for which an OTTI was previously recognized	0		0.1		0.1
Credit losses for which an OTTI was not previously recognized	0		0		0.3
Reductions for securities sold/matured	-0.1		0		0
Change in recoveries of future cash flows expected to be collected	-6.4	[1],[2]	-7.8	[1],[2]	-3.8	[1],[2]
Reductions for previously recognized credit impairments written-down to fair value	0	[3]	-0.2	[3]	-4	[3]
Ending balance	12.7		19.2		27.1
Commercial mortgage-backed securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Beginning balance	0.4		0.6		1.3
Credit losses for which an OTTI was previously recognized	0		0		0
Credit losses for which an OTTI was not previously recognized	0		0		0
Reductions for securities sold/matured	0		0		-0.2
Change in recoveries of future cash flows expected to be collected	0	[1],[2]	-0.2	[1],[2]	-0.2	[1],[2]
Reductions for previously recognized credit impairments written-down to fair value	0	[3]	0	[3]	-0.3	[3]
Ending balance	$0.40		$0.40		$0.60
[1]	Reflects expected recovery of prior period impairments that will be accreted into income over the remaining life of the security.
[2]	Includes $4.3 million, $2.6 million, and $1.4 million at December 31, 2014, 2013, and 2012, respectively, recognized in income in excess of the cash flows expected to be collected at the time of the write-downs.
[3]	Reflects reductions of prior credit impairments where the current credit impairment requires writing securities down to fair value (i.e., no remaining non-credit loss).

Investments_OTTI_Credit_Losses1

Investments OTTI Credit Losses Recognized in Earnings (Parenthetical) (Detail) (Actual Cash Flow Recovery, USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Actual Cash Flow Recovery
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Change in recoveries of future cash flows expected to be collected	$4.30	$2.60	$1.40

Investments_Components_of_Net_

Investments Components of Net Realized Gains (Losses) (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Gain (Loss) on Investments [Line Items]
Gross realized gains on securities sales	$290.20	$271.80	$360.60
Gross realized losses on securities sales	-29.9	-12.5	-31.1
Net realized gains (losses) on securities sales	260.3	259.3	329.5
Other-than-temporary impairment losses	-7.2	-6.1	-3.5
Total net realized gains (losses) on securities	224.2	318.4	306.8
Fixed maturities
Gain (Loss) on Investments [Line Items]
Gross realized gains on securities sales	92.9	76.9	115.4
Gross realized losses on securities sales	-22.6	-11.8	-2.9
Net realized gains (losses) on securities sales	70.3	65.1	112.5
Other-than-temporary impairment losses	0	-0.6	-1.7
Fixed maturities | U.S. government obligations
Gain (Loss) on Investments [Line Items]
Gross realized gains on securities sales	24	8.5	20.2
Gross realized losses on securities sales	-7.6	-3.7	-1.9
Net realized gains (losses) on securities sales	16.4	4.8	18.3
Fixed maturities | State and local government obligations
Gain (Loss) on Investments [Line Items]
Gross realized gains on securities sales	9.3	7.7	15
Gross realized losses on securities sales	-0.5	0	0
Net realized gains (losses) on securities sales	8.8	7.7	15
Fixed maturities | Corporate And Other Debt Securities
Gain (Loss) on Investments [Line Items]
Gross realized gains on securities sales	37.2	47.7	58.1
Gross realized losses on securities sales	-2.8	-6.2	-0.6
Net realized gains (losses) on securities sales	34.4	41.5	57.5
Fixed maturities | Residential mortgage-backed securities
Gain (Loss) on Investments [Line Items]
Gross realized gains on securities sales	2.7	3	1.2
Gross realized losses on securities sales	-0.2	0	0
Net realized gains (losses) on securities sales	2.5	3	1.2
Other-than-temporary impairment losses	0	-0.6	-1.6
Fixed maturities | Commercial mortgage-backed securities
Gain (Loss) on Investments [Line Items]
Gross realized gains on securities sales	17	10	19.3
Gross realized losses on securities sales	-8.3	-1.8	0
Net realized gains (losses) on securities sales	8.7	8.2	19.3
Other-than-temporary impairment losses	0	0	-0.1
Fixed maturities | Other asset-backed securities
Gain (Loss) on Investments [Line Items]
Gross realized gains on securities sales	0	0	0.9
Net realized gains (losses) on securities sales	0	0	0.9
Fixed maturities | Redeemable preferred stocks
Gain (Loss) on Investments [Line Items]
Gross realized gains on securities sales	2.7	0	0.7
Gross realized losses on securities sales	-3.2	-0.1	-0.4
Net realized gains (losses) on securities sales	-0.5	-0.1	0.3
Equity securities | Nonredeemable preferred stocks
Gain (Loss) on Investments [Line Items]
Gross realized gains on securities sales	90	126.3	78.2
Gross realized losses on securities sales	0	-0.1	-1.1
Net realized gains (losses) on securities sales	90	126.2	77.1
Equity securities | Common equities
Gain (Loss) on Investments [Line Items]
Gross realized gains on securities sales	107.3	68.6	167
Gross realized losses on securities sales	-7.3	-0.6	-27.1
Net realized gains (losses) on securities sales	100	68	139.9
Other-than-temporary impairment losses	-7.2	-5.5	-1.8
Hybrid and Derivative Instruments and Litigation Settlements
Gain (Loss) on Investments [Line Items]
Other gains (losses)	-28.9	65.2	-19.2
Hybrid and Derivative Instruments and Litigation Settlements | Litigation Settlements
Gain (Loss) on Investments [Line Items]
Other gains (losses)	4.7	2.2	9.6
Hybrid and Derivative Instruments and Litigation Settlements | Hybrid Preferred Stock
Gain (Loss) on Investments [Line Items]
Other gains (losses)	30.5	6.4	14.3
Hybrid and Derivative Instruments and Litigation Settlements | Derivative Instruments
Gain (Loss) on Investments [Line Items]
Other gains (losses)	($64.10)	$56.60	($43.10)

Investments_Components_of_Net_1

Investments Components of Net Investment Income (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	$408.40	$422	$443
Investment expenses	-18.9	-18.8	-15.4
Net investment income	389.5	403.2	427.6
Fixed maturities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	321.9	338	351.2
Fixed maturities | U.S. government obligations
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	46.2	50.2	49.8
Fixed maturities | State and local government obligations
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	50.1	48	51.1
Fixed maturities | Foreign government obligations
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	0.4	0.2	0
Fixed maturities | Corporate debt securities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	82.1	98.8	107.5
Fixed maturities | Residential mortgage-backed securities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	44.9	28.1	16.1
Fixed maturities | Commercial mortgage-backed securities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	66	74.8	82.2
Fixed maturities | Other asset-backed securities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	16.7	16.7	20.3
Fixed maturities | Redeemable preferred stocks
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	15.5	21.2	24.2
Equity securities | Nonredeemable preferred stocks
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	38.6	36.2	43.8
Equity securities | Common equities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	46.6	45.8	44.9
Short-term investments
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	$1.30	$2	$3.10

Investments_Derivative_Instrum

Investments Derivative Instruments (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Derivative [Line Items]
Balance Sheet - Fair Value	$15.80	[1]	$68.10	[1]
Income Statement - Net Realized Gain (Loss) on Securities	-64.1		56.6		-43.1
Hedging Instrument | Closed Positions | Ineffective Cash Flow Hedge
Derivative [Line Items]
Notional Value	44	[2]	54	[2]	31	[2]
Purpose	Manage interest rate risk		Manage interest rate risk		Manage interest rate risk
Balance Sheet - Fair Value	0	[1]	0	[1]
Income Statement - Net Realized Gain (Loss) on Securities	0.5		0.8		0.6
Non-hedging Instruments | Closed Positions | Interest Rate Swaps
Derivative [Line Items]
Notional Value	0	[2]	1,263	[2]	0	[2]
Purpose			Manage portfolio duration
Balance Sheet - Fair Value	0	[1]	0	[1]
Income Statement - Net Realized Gain (Loss) on Securities	0		-4		0
Non-hedging Instruments | Closed Positions | Corporate Credit Default Swaps
Derivative [Line Items]
Notional Value	0	[2]	0	[2]	25	[2]
Purpose					Manage credit risk
Balance Sheet - Fair Value	0	[1]	0	[1]
Income Statement - Net Realized Gain (Loss) on Securities	0		0		-1
Non-hedging Instruments | Assets | Interest Rate Swaps | Fixed maturities
Derivative [Line Items]
Notional Value	750	[2]	750	[2]	0	[2]
Purpose	Manage portfolio duration		Manage portfolio duration
Balance Sheet - Fair Value	15.8	[1]	68.1	[1]
Income Statement - Net Realized Gain (Loss) on Securities	-64.6		59.8		0
Non-hedging Instruments | Liabilities | Interest Rate Swaps | Other Liabilities
Derivative [Line Items]
Notional Value	0	[2]	0	[2]	1,263	[2]
Purpose					Manage portfolio duration
Balance Sheet - Fair Value	0	[1]	0	[1]
Income Statement - Net Realized Gain (Loss) on Securities	$0		$0		($42.70)
[1]	To the extent we hold both derivative assets and liabilities with the same counterparty that are subject to an enforceable master netting arrangement, we expect that we will report them on a gross basis on our balance sheets, consistent with our historical presentation.
[2]	The amounts represent the value held at year end for open positions and the maximum amount held during the year for closed positions.

Investments_Additional_Informa

Investments - Additional Information (Detail) (USD $)	12 Months Ended			1 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Apr. 25, 2014
Schedule of Investments [Line Items]
Short-term Investments	$2,149,000,000	$1,272,600,000
Open reverse repurchase commitments	0	200,000,000
Largest Outstanding Balance of Reverse Repurchase Agreements	500,000,000
RRP Largest Outstanding Balance Number of Days Open	1 day
Reverse Repurchase Agreement Average Daily Balance	158,800,000
Principal amount of bonds and certificates of deposit on deposit to meet state insurance regulatory and/or rating agency requirements	153,700,000
Fair value of fixed-maturity securities that were non-income producing during the preceding 12 months	0
Gross Unrealized Losses	49,200,000	126,000,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	318	423
Trading securities	0	0
Net realized gains (losses) on securities	232,100,000	324,500,000	314,800,000
Reclassification out of Accumulated Other Comprehensive Income
Schedule of Investments [Line Items]
Cash flow hedge gain recognized as an adjustment to interest expense	2,000,000	2,100,000	2,100,000
4.35% Senior Notes due 2044
Schedule of Investments [Line Items]
Unrealized Gain (Loss)	-1,600,000			-1,600,000
Senior notes, issuance amount	350,000,000	0		350,000,000
Debt Instrument, Interest Rate, Stated Percentage	4.35%			4.35%
Equity securities
Schedule of Investments [Line Items]
Gross Unrealized Losses	16,500,000	6,900,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	28	31
Equity securities | Common equities
Schedule of Investments [Line Items]
Gross Unrealized Losses	10,100,000	2,400,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	20	24
Equity securities | Nonredeemable preferred stocks
Schedule of Investments [Line Items]
Gross Unrealized Losses	6,400,000	4,500,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	8	7
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Percentage Decline	3.00%
Fixed maturities
Schedule of Investments [Line Items]
Gross Unrealized Losses	32,700,000	119,100,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	290	392
Fixed maturities | Corporate debt securities
Schedule of Investments [Line Items]
Percentage which the issuer receives the security back at once the change of control is triggered	1.00%
Realized investment losses	9,300,000
Gross Unrealized Losses	10,400,000	20,400,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	53	51
Fixed Income Securities
Schedule of Investments [Line Items]
Gross Unrealized Losses	39,100,000
Foreign Government Debt
Schedule of Investments [Line Items]
Short-term Investments	5,700,000	6,300,000
Corporate Credit Default Swaps
Schedule of Investments [Line Items]
Number of derivative positions held during the period	0	0
Corporate Credit Default Swaps | Financial Services Sector
Schedule of Investments [Line Items]
Number of derivative positions closed during the period			1
Derivative Maturity1			5 years
Interest Rate Swaps
Schedule of Investments [Line Items]
Number of derivative positions closed during the period		3
Cash collateral delivered to the counterparties			105,000,000
Cash collateral received from counterparty	16,100,000	62,700,000
Interest Rate Swaps | Opened in 2009 | Closed Positions | Nine Year Time Horizon
Schedule of Investments [Line Items]
Number of derivative positions closed during the period		1
Derivative Maturity1		9 years
Interest Rate Swaps | Opened in 2011 | Closed Positions | Five Year Time Horizon
Schedule of Investments [Line Items]
Number of derivative positions closed during the period		2
Derivative Maturity1		5 years
Value Of Securities Of Any One Issuer Excluding US Government Obligations Exceeding 10 % Of Total Shareholders Equity
Schedule of Investments [Line Items]
Aggregate cost or fair value of securities	0	0
Categories of Investments, Marketable Securities, Trading Securities
Schedule of Investments [Line Items]
Net realized gains (losses) on securities	0	0	0
Russell One Thousand | Equity securities | Common equities
Schedule of Investments [Line Items]
Percentage of common stock portfolio	88.00%
Managed Equity Strategy | Equity securities | Common equities
Schedule of Investments [Line Items]
Percentage of common stock portfolio	12.00%
Non-hedging Instruments | Interest Rate Swaps | Fixed maturities | Assets
Schedule of Investments [Line Items]
Derivative, Loss on Derivative	$52,300,000

Fair_Value_Composition_of_Inve

Fair Value Composition of Investment Portfolio by Major Security Type (Detail) (USD $)	Dec. 31, 2014		Dec. 31, 2013
In Millions, unless otherwise specified
Fair Value Measurements [Line Items]
Portfolio	$19,018	[1],[2]	$18,054.70	[1],[2]
Long-term Debt, Fair Value	2,527.50		2,073.70
Debt	2,164.70	[3]	1,860.90	[3]
Fixed maturities
Fair Value Measurements [Line Items]
Portfolio	13,549.20		13,540.40
Fixed maturities | Redeemable preferred stocks
Fair Value Measurements [Line Items]
Portfolio	279.2		313.9
Fixed maturities | Redeemable preferred stocks | Financials
Fair Value Measurements [Line Items]
Portfolio	97.9		102.8
Fixed maturities | Redeemable preferred stocks | Utilities
Fair Value Measurements [Line Items]
Portfolio	65.3		65.6
Fixed maturities | Redeemable preferred stocks | Industrials
Fair Value Measurements [Line Items]
Portfolio	116		145.5
Fixed maturities | Debt Securities
Fair Value Measurements [Line Items]
Portfolio	7,657.20		8,860.40
Fixed maturities | Debt Securities | U.S. government obligations
Fair Value Measurements [Line Items]
Portfolio	2,667.10		3,662.20
Fixed maturities | Debt Securities | State and local government obligations
Fair Value Measurements [Line Items]
Portfolio	2,139.20		2,256
Fixed maturities | Debt Securities | Foreign government obligations
Fair Value Measurements [Line Items]
Portfolio	14.2		15.6
Fixed maturities | Debt Securities | Corporate debt securities
Fair Value Measurements [Line Items]
Portfolio	2,836.70		2,926.60
Fixed maturities | Asset-backed Securities
Fair Value Measurements [Line Items]
Portfolio	5,612.80		4,366.10
Fixed maturities | Asset-backed Securities | Residential mortgage-backed securities
Fair Value Measurements [Line Items]
Portfolio	1,658.50		1,127.90
Fixed maturities | Asset-backed Securities | Commercial mortgage-backed securities
Fair Value Measurements [Line Items]
Portfolio	2,315.60		2,160.50
Fixed maturities | Asset-backed Securities | Other asset-backed securities
Fair Value Measurements [Line Items]
Portfolio	1,638.70		1,077.70
Equity securities | Nonredeemable preferred stocks
Fair Value Measurements [Line Items]
Portfolio	827.5		711.2
Equity securities | Nonredeemable preferred stocks | Financials
Fair Value Measurements [Line Items]
Portfolio	827.5		694.4
Equity securities | Nonredeemable preferred stocks | Utilities
Fair Value Measurements [Line Items]
Portfolio	0		16.8
Equity securities | Common equities
Fair Value Measurements [Line Items]
Portfolio	2,492.30		2,530.50
Equity securities | Common equities | Common equities
Fair Value Measurements [Line Items]
Portfolio	2,491.90		2,530
Equity securities | Common equities | Other risk investments
Fair Value Measurements [Line Items]
Portfolio	0.4		0.5
Total Fixed Maturities and Equity Securities
Fair Value Measurements [Line Items]
Portfolio	16,869		16,782.10
Short-term investments
Fair Value Measurements [Line Items]
Portfolio	2,149		1,272.60
Carrying (Reported) Amount, Fair Value Disclosure
Fair Value Measurements [Line Items]
Portfolio	17,402.80		16,584.70
Debt	2,164.70		1,860.90
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities
Fair Value Measurements [Line Items]
Portfolio	13,374.20		13,415.30
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Redeemable preferred stocks
Fair Value Measurements [Line Items]
Portfolio	260.2		299.5
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Redeemable preferred stocks | Financials
Fair Value Measurements [Line Items]
Portfolio	77.3		84.2
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Redeemable preferred stocks | Utilities
Fair Value Measurements [Line Items]
Portfolio	65		64.9
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Redeemable preferred stocks | Industrials
Fair Value Measurements [Line Items]
Portfolio	117.9		150.4
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Debt Securities
Fair Value Measurements [Line Items]
Portfolio	7,564.90		8,778.30
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Debt Securities | U.S. government obligations
Fair Value Measurements [Line Items]
Portfolio	2,641.10		3,630.40
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Debt Securities | State and local government obligations
Fair Value Measurements [Line Items]
Portfolio	2,095.70		2,247.30
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Debt Securities | Foreign government obligations
Fair Value Measurements [Line Items]
Portfolio	14.2		15.6
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Debt Securities | Corporate debt securities
Fair Value Measurements [Line Items]
Portfolio	2,813.90		2,885
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Asset-backed Securities
Fair Value Measurements [Line Items]
Portfolio	5,549.10		4,337.50
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Asset-backed Securities | Residential mortgage-backed securities
Fair Value Measurements [Line Items]
Portfolio	1,635.50		1,110.10
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Asset-backed Securities | Commercial mortgage-backed securities
Fair Value Measurements [Line Items]
Portfolio	2,278.70		2,154.40
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Asset-backed Securities | Other asset-backed securities
Fair Value Measurements [Line Items]
Portfolio	1,634.90		1,073
Carrying (Reported) Amount, Fair Value Disclosure | Equity securities | Nonredeemable preferred stocks
Fair Value Measurements [Line Items]
Portfolio	590.4		445.7
Carrying (Reported) Amount, Fair Value Disclosure | Equity securities | Nonredeemable preferred stocks | Financials
Fair Value Measurements [Line Items]
Portfolio	590.4		431.5
Carrying (Reported) Amount, Fair Value Disclosure | Equity securities | Nonredeemable preferred stocks | Utilities
Fair Value Measurements [Line Items]
Portfolio	0		14.2
Carrying (Reported) Amount, Fair Value Disclosure | Equity securities | Common equities
Fair Value Measurements [Line Items]
Portfolio	1,289.20		1,451.10
Carrying (Reported) Amount, Fair Value Disclosure | Equity securities | Common equities | Common equities
Fair Value Measurements [Line Items]
Portfolio	1,288.80		1,450.60
Carrying (Reported) Amount, Fair Value Disclosure | Equity securities | Common equities | Other risk investments
Fair Value Measurements [Line Items]
Portfolio	0.4		0.5
Carrying (Reported) Amount, Fair Value Disclosure | Total Fixed Maturities and Equity Securities
Fair Value Measurements [Line Items]
Portfolio	15,253.80		15,312.10
Carrying (Reported) Amount, Fair Value Disclosure | Short-term investments
Fair Value Measurements [Line Items]
Portfolio	2,149		1,272.60
Fair Value, Inputs, Level 1
Fair Value Measurements [Line Items]
Portfolio	7,314.30		7,436.40
Long-term Debt, Fair Value	0		0
Fair Value, Inputs, Level 1 | Fixed maturities
Fair Value Measurements [Line Items]
Portfolio	2,681.30		3,677.80
Fair Value, Inputs, Level 1 | Fixed maturities | Redeemable preferred stocks
Fair Value Measurements [Line Items]
Portfolio	0		0
Fair Value, Inputs, Level 1 | Fixed maturities | Redeemable preferred stocks | Financials
Fair Value Measurements [Line Items]
Portfolio	0		0
Fair Value, Inputs, Level 1 | Fixed maturities | Redeemable preferred stocks | Utilities
Fair Value Measurements [Line Items]
Portfolio	0		0
Fair Value, Inputs, Level 1 | Fixed maturities | Redeemable preferred stocks | Industrials
Fair Value Measurements [Line Items]
Portfolio	0		0
Fair Value, Inputs, Level 1 | Fixed maturities | Debt Securities
Fair Value Measurements [Line Items]
Portfolio	2,681.30		3,677.80
Fair Value, Inputs, Level 1 | Fixed maturities | Debt Securities | U.S. government obligations
Fair Value Measurements [Line Items]
Portfolio	2,667.10		3,662.20
Fair Value, Inputs, Level 1 | Fixed maturities | Debt Securities | State and local government obligations
Fair Value Measurements [Line Items]
Portfolio	0		0
Fair Value, Inputs, Level 1 | Fixed maturities | Debt Securities | Foreign government obligations
Fair Value Measurements [Line Items]
Portfolio	14.2		15.6
Fair Value, Inputs, Level 1 | Fixed maturities | Debt Securities | Corporate debt securities
Fair Value Measurements [Line Items]
Portfolio	0		0
Fair Value, Inputs, Level 1 | Fixed maturities | Asset-backed Securities
Fair Value Measurements [Line Items]
Portfolio	0		0
Fair Value, Inputs, Level 1 | Fixed maturities | Asset-backed Securities | Residential mortgage-backed securities
Fair Value Measurements [Line Items]
Portfolio	0		0
Fair Value, Inputs, Level 1 | Fixed maturities | Asset-backed Securities | Commercial mortgage-backed securities
Fair Value Measurements [Line Items]
Portfolio	0		0
Fair Value, Inputs, Level 1 | Fixed maturities | Asset-backed Securities | Other asset-backed securities
Fair Value Measurements [Line Items]
Portfolio	0		0
Fair Value, Inputs, Level 1 | Equity securities | Nonredeemable preferred stocks
Fair Value Measurements [Line Items]
Portfolio	204.1		240.8
Fair Value, Inputs, Level 1 | Equity securities | Nonredeemable preferred stocks | Financials
Fair Value Measurements [Line Items]
Portfolio	204.1		240.8
Fair Value, Inputs, Level 1 | Equity securities | Nonredeemable preferred stocks | Utilities
Fair Value Measurements [Line Items]
Portfolio	0		0
Fair Value, Inputs, Level 1 | Equity securities | Common equities
Fair Value Measurements [Line Items]
Portfolio	2,491.90		2,530
Fair Value, Inputs, Level 1 | Equity securities | Common equities | Common equities
Fair Value Measurements [Line Items]
Portfolio	2,491.90		2,530
Fair Value, Inputs, Level 1 | Equity securities | Common equities | Other risk investments
Fair Value Measurements [Line Items]
Portfolio	0		0
Fair Value, Inputs, Level 1 | Total Fixed Maturities and Equity Securities
Fair Value Measurements [Line Items]
Portfolio	5,377.30		6,448.60
Fair Value, Inputs, Level 1 | Short-term investments
Fair Value Measurements [Line Items]
Portfolio	1,937		987.8
Fair Value, Inputs, Level 2
Fair Value Measurements [Line Items]
Portfolio	11,622.40		10,549.60
Long-term Debt, Fair Value	2,527.50		2,073.70
Fair Value, Inputs, Level 2 | Fixed maturities
Fair Value Measurements [Line Items]
Portfolio	10,856.30		9,833.40
Fair Value, Inputs, Level 2 | Fixed maturities | Redeemable preferred stocks
Fair Value Measurements [Line Items]
Portfolio	279.2		313.9
Fair Value, Inputs, Level 2 | Fixed maturities | Redeemable preferred stocks | Financials
Fair Value Measurements [Line Items]
Portfolio	97.9		102.8
Fair Value, Inputs, Level 2 | Fixed maturities | Redeemable preferred stocks | Utilities
Fair Value Measurements [Line Items]
Portfolio	65.3		65.6
Fair Value, Inputs, Level 2 | Fixed maturities | Redeemable preferred stocks | Industrials
Fair Value Measurements [Line Items]
Portfolio	116		145.5
Fair Value, Inputs, Level 2 | Fixed maturities | Debt Securities
Fair Value Measurements [Line Items]
Portfolio	4,975.90		5,182.60
Fair Value, Inputs, Level 2 | Fixed maturities | Debt Securities | U.S. government obligations
Fair Value Measurements [Line Items]
Portfolio	0		0
Fair Value, Inputs, Level 2 | Fixed maturities | Debt Securities | State and local government obligations
Fair Value Measurements [Line Items]
Portfolio	2,139.20		2,256
Fair Value, Inputs, Level 2 | Fixed maturities | Debt Securities | Foreign government obligations
Fair Value Measurements [Line Items]
Portfolio	0		0
Fair Value, Inputs, Level 2 | Fixed maturities | Debt Securities | Corporate debt securities
Fair Value Measurements [Line Items]
Portfolio	2,836.70		2,926.60
Fair Value, Inputs, Level 2 | Fixed maturities | Asset-backed Securities
Fair Value Measurements [Line Items]
Portfolio	5,601.20		4,336.90
Fair Value, Inputs, Level 2 | Fixed maturities | Asset-backed Securities | Residential mortgage-backed securities
Fair Value Measurements [Line Items]
Portfolio	1,658.50		1,127.70
Fair Value, Inputs, Level 2 | Fixed maturities | Asset-backed Securities | Commercial mortgage-backed securities
Fair Value Measurements [Line Items]
Portfolio	2,304		2,131.50
Fair Value, Inputs, Level 2 | Fixed maturities | Asset-backed Securities | Other asset-backed securities
Fair Value Measurements [Line Items]
Portfolio	1,638.70		1,077.70
Fair Value, Inputs, Level 2 | Equity securities | Nonredeemable preferred stocks
Fair Value Measurements [Line Items]
Portfolio	554.1		431.4
Fair Value, Inputs, Level 2 | Equity securities | Nonredeemable preferred stocks | Financials
Fair Value Measurements [Line Items]
Portfolio	554.1		414.6
Fair Value, Inputs, Level 2 | Equity securities | Nonredeemable preferred stocks | Utilities
Fair Value Measurements [Line Items]
Portfolio	0		16.8
Fair Value, Inputs, Level 2 | Equity securities | Common equities
Fair Value Measurements [Line Items]
Portfolio	0		0
Fair Value, Inputs, Level 2 | Equity securities | Common equities | Common equities
Fair Value Measurements [Line Items]
Portfolio	0		0
Fair Value, Inputs, Level 2 | Equity securities | Common equities | Other risk investments
Fair Value Measurements [Line Items]
Portfolio	0		0
Fair Value, Inputs, Level 2 | Total Fixed Maturities and Equity Securities
Fair Value Measurements [Line Items]
Portfolio	11,410.40		10,264.80
Fair Value, Inputs, Level 2 | Short-term investments
Fair Value Measurements [Line Items]
Portfolio	212		284.8
Fair Value, Inputs, Level 3
Fair Value Measurements [Line Items]
Portfolio	81.3		68.7
Long-term Debt, Fair Value	0		0
Fair Value, Inputs, Level 3 | Fixed maturities
Fair Value Measurements [Line Items]
Portfolio	11.6		29.2
Fair Value, Inputs, Level 3 | Fixed maturities | Redeemable preferred stocks
Fair Value Measurements [Line Items]
Portfolio	0		0
Fair Value, Inputs, Level 3 | Fixed maturities | Redeemable preferred stocks | Financials
Fair Value Measurements [Line Items]
Portfolio	0		0
Fair Value, Inputs, Level 3 | Fixed maturities | Redeemable preferred stocks | Utilities
Fair Value Measurements [Line Items]
Portfolio	0		0
Fair Value, Inputs, Level 3 | Fixed maturities | Redeemable preferred stocks | Industrials
Fair Value Measurements [Line Items]
Portfolio	0		0
Fair Value, Inputs, Level 3 | Fixed maturities | Debt Securities
Fair Value Measurements [Line Items]
Portfolio	0		0
Fair Value, Inputs, Level 3 | Fixed maturities | Debt Securities | U.S. government obligations
Fair Value Measurements [Line Items]
Portfolio	0		0
Fair Value, Inputs, Level 3 | Fixed maturities | Debt Securities | State and local government obligations
Fair Value Measurements [Line Items]
Portfolio	0		0
Fair Value, Inputs, Level 3 | Fixed maturities | Debt Securities | Foreign government obligations
Fair Value Measurements [Line Items]
Portfolio	0		0
Fair Value, Inputs, Level 3 | Fixed maturities | Debt Securities | Corporate debt securities
Fair Value Measurements [Line Items]
Portfolio	0		0
Fair Value, Inputs, Level 3 | Fixed maturities | Asset-backed Securities
Fair Value Measurements [Line Items]
Portfolio	11.6		29.2
Fair Value, Inputs, Level 3 | Fixed maturities | Asset-backed Securities | Residential mortgage-backed securities
Fair Value Measurements [Line Items]
Portfolio	0		0.2
Fair Value, Inputs, Level 3 | Fixed maturities | Asset-backed Securities | Commercial mortgage-backed securities
Fair Value Measurements [Line Items]
Portfolio	11.6		29
Fair Value, Inputs, Level 3 | Fixed maturities | Asset-backed Securities | Other asset-backed securities
Fair Value Measurements [Line Items]
Portfolio	0		0
Fair Value, Inputs, Level 3 | Equity securities | Nonredeemable preferred stocks
Fair Value Measurements [Line Items]
Portfolio	69.3		39
Fair Value, Inputs, Level 3 | Equity securities | Nonredeemable preferred stocks | Financials
Fair Value Measurements [Line Items]
Portfolio	69.3		39
Fair Value, Inputs, Level 3 | Equity securities | Nonredeemable preferred stocks | Utilities
Fair Value Measurements [Line Items]
Portfolio	0		0
Fair Value, Inputs, Level 3 | Equity securities | Common equities
Fair Value Measurements [Line Items]
Portfolio	0.4		0.5
Fair Value, Inputs, Level 3 | Equity securities | Common equities | Common equities
Fair Value Measurements [Line Items]
Portfolio	0		0
Fair Value, Inputs, Level 3 | Equity securities | Common equities | Other risk investments
Fair Value Measurements [Line Items]
Portfolio	0.4		0.5
Fair Value, Inputs, Level 3 | Total Fixed Maturities and Equity Securities
Fair Value Measurements [Line Items]
Portfolio	81.3		68.7
Fair Value, Inputs, Level 3 | Short-term investments
Fair Value Measurements [Line Items]
Portfolio	$0		$0
[1]	The total fair value of the portfolio included $1.9 billion and $1.8 billion at December 31, 2014 and 2013, respectively, of securities held in a consolidated, non-insurance subsidiary of the holding company, net of any unsettled security transactions.
[2]	Our portfolio reflects the effect of unsettled security transactions and collateral on open derivative positions; at December 31, 2014, $31.3 million was included in "other liabilities," compared to $61.3 million at December 31, 2013.
[3]	Consists of long-term debt. See Note 4 – Debt for further discussion.

Fair_Value_Summary_of_Changes_

Fair Value Summary of Changes in Fair Value Associated With Level 3 Assets (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Fair Value	$68.70		$114.70
Calls/ Maturities/ Paydowns	-3.7		-32.5
Purchases	0		125.4
Sales	-0.1		-2.4
Net Realized (Gain)/Loss on Sales	0.1		-36
Change in Valuation	29.9		40.9
Net Transfers In (Out)	-13.6	[1]	-141.4	[2]
Ending Fair value	81.3		68.7
Fixed maturities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Fair Value	29.2		70.8
Calls/ Maturities/ Paydowns	-3.6		-32
Purchases	0		125.1
Sales	-0.1		0
Net Realized (Gain)/Loss on Sales	0.1		0
Change in Valuation	-0.4		6.7
Net Transfers In (Out)	-13.6	[1]	-141.4	[2]
Ending Fair value	11.6		29.2
Fixed maturities | Asset-backed Securities | Residential mortgage-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Fair Value	0.2		45.5
Calls/ Maturities/ Paydowns	0		-28.6
Purchases	0		125.1
Sales	-0.1		0
Net Realized (Gain)/Loss on Sales	0.1		0
Change in Valuation	-0.2		-0.4
Net Transfers In (Out)	0	[1]	-141.4	[2]
Ending Fair value	0		0.2
Fixed maturities | Asset-backed Securities | Commercial mortgage-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Fair Value	29		25.3
Calls/ Maturities/ Paydowns	-3.6		-3.4
Purchases	0		0
Sales	0		0
Net Realized (Gain)/Loss on Sales	0		0
Change in Valuation	-0.2		7.1
Net Transfers In (Out)	-13.6	[1]	0	[2]
Ending Fair value	11.6		29
Equity securities | Nonredeemable preferred stocks | Financials
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Fair Value	39	[3],[4]	31.9	[3]
Calls/ Maturities/ Paydowns	0	[4]	0	[3]
Purchases	0	[4]	0	[3]
Sales	0	[4]	0	[3]
Net Realized (Gain)/Loss on Sales	0	[4]	0	[3]
Change in Valuation	30.3	[4]	7.1	[3]
Net Transfers In (Out)	0	[1],[4]	0	[2],[3]
Ending Fair value	69.3	[4]	39	[3],[4]
Equity securities | Common equities | Other risk investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Fair Value	0.5		12
Calls/ Maturities/ Paydowns	-0.1		-0.5
Purchases	0		0.3
Sales	0		-2.4
Net Realized (Gain)/Loss on Sales	0		-36
Change in Valuation	0		27.1
Net Transfers In (Out)	0	[1]	0	[2]
Ending Fair value	$0.40		$0.50
[1]	The $13.6 million was transferred out of Level 3 and into Level 2 due to an improvement in the security's underlying collateral and an increase in liquidity and market activity in comparable securities.
[2]	The $141.4 million was transferred out of Level 3 and into Level 2 due to an increase in liquidity and trading volume in the market.
[3]	The $7.1 million represents a net holding period gain on our investment in ARX Holding Corp., which is reflected in net realized gains (losses) on securities in the comprehensive income statement.
[4]	The $30.3 million represents a net holding period gain on our investment in ARX Holding Corp., which is reflected in net realized gains (losses) on securities in the comprehensive income statement.

Fair_Value_Summary_of_Changes_1

Fair Value Summary of Changes in Fair Value Associated With Level 3 Assets (Parenthetical) (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Net realized gains (losses) on securities	$232,100,000	$324,500,000	$314,800,000
Equity securities | Nonredeemable preferred stocks | Hybrid Securities | Financials
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Net realized gains (losses) on securities	30,300,000	7,100,000
Asset-backed Securities | Fixed maturities | Residential mortgage-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Transferred out of Level 3 into Level 2		-141,400,000
Asset-backed Securities | Fixed maturities | Commercial mortgage-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Transferred out of Level 3 into Level 2	($13,600,000)

Fair_Value_Summary_of_Quantita

Fair Value Summary of Quantitative Information about Level 3 Fair Value Measurements (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
	Investment		Investment
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$19,018	[1],[2]	$18,054.70	[1],[2]
Fair Value, Inputs, Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	81.3		68.7
Fair Value, Inputs, Level 3 | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	11.6		29.2
Fair Value, Inputs, Level 3 | Fixed maturities | Asset-backed Securities | Residential mortgage-backed securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	0
External Pricing | Fair Value, Inputs, Level 3 | Fixed maturities | Asset-backed Securities | Residential mortgage-backed securities | Prepayment rate zero percent
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Number of securities			1
Fair Value			0.2
Valuation Technique			External vendor
Unobservable Input, prepayment rate			0.00%
External Pricing | Fair Value, Inputs, Level 3 | Fixed maturities | Asset-backed Securities | Commercial mortgage-backed securities | Prepayment rate zero percent
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Number of securities	1		2
Fair Value	11.6		29
Valuation Technique	External vendor		External vendor
Unobservable Input, prepayment rate	0.00%		0.00%
Internal Pricing | Fair Value, Inputs, Level 3 | Equity securities | Nonredeemable preferred stocks
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Number of securities	1		1
Fair Value	69.3		39
Internal Pricing | Fair Value, Inputs, Level 3 | Equity securities | Nonredeemable preferred stocks | Financials
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	69.3		39
Valuation Technique	Multiple of tangible net book value		Multiple of tangible net book value
Unobservable Input, price to book ratio multiple	2.6		1.9
Subtotal Level 3 Securities | Fair Value, Inputs, Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	80.9		68.2
Third Party Pricing Exemption Securities | Fair Value, Inputs, Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$0.40	[3]	$0.50	[3]
[1]	The total fair value of the portfolio included $1.9 billion and $1.8 billion at December 31, 2014 and 2013, respectively, of securities held in a consolidated, non-insurance subsidiary of the holding company, net of any unsettled security transactions.
[2]	Our portfolio reflects the effect of unsettled security transactions and collateral on open derivative positions; at December 31, 2014, $31.3 million was included in "other liabilities," compared to $61.3 million at December 31, 2013.
[3]	The fair values for these securities were obtained from non-binding external sources where unobservable inputs are not reasonably available to us.

Fair_Value_Additional_Informat

Fair Value - Additional Information (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2014
	Investment		Investment
Fair Value Measurements [Line Items]
Number of securities transferred out of Level 2 into Level 1	0
Quoted prices percentage of fair value assets	100.00%	[1],[2]	100.00%	[1],[2]
Portfolio	$18,054.70	[1],[2]	$19,018	[1],[2]
Fair Value, Inputs, Level 1
Fair Value Measurements [Line Items]
Portfolio	7,436.40		7,314.30
Fair Value, Inputs, Level 1 | Vendor Quoted Pricing
Fair Value Measurements [Line Items]
Quoted prices percentage of fair value assets	56.00%		50.00%
Fair Value, Inputs, Level 2
Fair Value Measurements [Line Items]
Portfolio	10,549.60		11,622.40
Fair Value, Inputs, Level 2 | Vendor Quoted Pricing
Fair Value Measurements [Line Items]
Quoted prices percentage of fair value assets	98.00%		97.00%
Fair Value, Inputs, Level 2 | Dealer Quoted Pricing
Fair Value Measurements [Line Items]
Quoted prices percentage of fair value assets	2.00%		3.00%
Fair Value, Inputs, Level 3
Fair Value Measurements [Line Items]
Portfolio	68.7		81.3
Nonredeemable preferred stocks | Equity securities
Fair Value Measurements [Line Items]
Number of securities transferred out of Level 2 into Level 1			2
Fair Value, Assets, Level 2 to Level 1 Transfers, Amount			41.7
Nonredeemable preferred stocks | Fair Value, Inputs, Level 3 | Equity securities | Internal Pricing
Fair Value Measurements [Line Items]
Number of securities	1		1
Portfolio	$39		$69.30
[1]	The total fair value of the portfolio included $1.9 billion and $1.8 billion at December 31, 2014 and 2013, respectively, of securities held in a consolidated, non-insurance subsidiary of the holding company, net of any unsettled security transactions.
[2]	Our portfolio reflects the effect of unsettled security transactions and collateral on open derivative positions; at December 31, 2014, $31.3 million was included in "other liabilities," compared to $61.3 million at December 31, 2013.

Debt_Detail

Debt (Detail) (USD $)	Dec. 31, 2014		Dec. 31, 2013
In Millions, unless otherwise specified
Debt Instrument [Line Items]
Carrying Value	$2,164.70	[1]	$1,860.90	[1]
Fair Value	2,527.50		2,073.70
3.75% Senior Notes due 2021
Debt Instrument [Line Items]
Carrying Value	497.8		497.6
Fair Value	535.6		509.1
6 5/8% Senior Notes due 2029
Debt Instrument [Line Items]
Carrying Value	295.5		295.3
Fair Value	400.6		359.6
6.25% Senior Notes due 2032
Debt Instrument [Line Items]
Carrying Value	394.8		394.6
Fair Value	527.9		473.7
4.35% Senior Notes due 2044
Debt Instrument [Line Items]
Carrying Value	346.3		0
Fair Value	378.9		0
6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067
Debt Instrument [Line Items]
Carrying Value	630.3		673.4
Fair Value	$684.50		$731.30
[1]	Consists of long-term debt. See Note 4 – Debt for further discussion.

Debt_Parenthetical_Detail

Debt (Parenthetical) (Detail) (USD $)	Dec. 31, 2014	Apr. 25, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Debt instrument, outstanding	$2,182,800,000
3.75% Senior Notes due 2021
Debt Instrument [Line Items]
Senior notes, issuance amount	500,000,000		500,000,000
Debt Instrument, Interest Rate, Stated Percentage	3.75%
6 5/8% Senior Notes due 2029
Debt Instrument [Line Items]
Senior notes, issuance amount	300,000,000		300,000,000
Debt Instrument, Interest Rate, Stated Percentage	6.63%
6.25% Senior Notes due 2032
Debt Instrument [Line Items]
Senior notes, issuance amount	400,000,000		400,000,000
Debt Instrument, Interest Rate, Stated Percentage	6.25%
4.35% Senior Notes due 2044
Debt Instrument [Line Items]
Senior notes, issuance amount	350,000,000	350,000,000	0
Debt Instrument, Interest Rate, Stated Percentage	4.35%	4.35%
6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067
Debt Instrument [Line Items]
Senior notes, issuance amount	1,000,000,000		1,000,000,000
Debt instrument, outstanding	$632,800,000		$677,100,000
Debt Instrument, Interest Rate, Stated Percentage	6.70%

Debt_Unrealized_Gains_Losses_F

Debt Unrealized Gains (Losses) From Debt Hedges Included In Accumulated Other (Detail) (USD $)	12 Months Ended			1 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 1999	Dec. 31, 2002	Apr. 25, 2014	Dec. 31, 2014	Dec. 31, 2007
3.75% Senior Notes due 2021
Debt Instrument [Line Items]
Unrealized Gain (Loss)	($5.10)
Unamortized Balance					-3.6
6 5/8% Senior Notes due 2029
Debt Instrument [Line Items]
Unrealized Gain (Loss)		-4.2
Unamortized Balance					-3.2
6.25% Senior Notes due 2032
Debt Instrument [Line Items]
Unrealized Gain (Loss)			5.1
Unamortized Balance					4
4.35% Senior Notes due 2044
Debt Instrument [Line Items]
Unrealized Gain (Loss)				-1.6	-1.6
Unamortized Balance					-1.6
6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067
Debt Instrument [Line Items]
Unrealized Gain (Loss)						34.4
Unamortized Balance					$6.60

Debt_Aggregate_Principal_Payme

Debt Aggregate Principal Payments On Debt Outstanding (Detail) (USD $)	Dec. 31, 2014
In Millions, unless otherwise specified
Debt Disclosure [Abstract]
2015	$0
2016	0
2017	0
2018	0
2019	0
Thereafter	2,182.80
Total	$2,182.80

Debt_Additional_Information_De

Debt - Additional Information (Detail) (USD $)	12 Months Ended			1 Months Ended	12 Months Ended	1 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Apr. 25, 2014	Dec. 31, 2007	Oct. 31, 2013
Debt Instrument [Line Items]
Debt interest payments	Interest on all debt is payable semiannually at the stated rates. However, the 6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067 (the “6.70% Debentures”) will only bear interest at this fixed annual rate through, but excluding, June 15, 2017. Thereafter, the 6.70% Debentures will bear interest at an annual rate equal to the three-month LIBOR plus 2.0175%, and interest will be payable quarterly until the 6.70% Debentures are redeemed or retired
Interest payment frequency	Payable semiannually
Payment of debt	$0	$150,000,000	$350,000,000
Gains (losses) on extinguishment of debt	-4,800,000	-4,300,000	-1,800,000
Discretionary Line of Credit
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	100,000,000	100,000,000
Line of Credit Facility, Interest Rate Description	advances under the Line of Credit (if any) will bear interest at a variable rate equal to the higher of PNC's Prime Rate or the sum of the Federal Funds Open Rate plus 50 basis points.
Line of Credit Facility, Amount Outstanding	0	0
Discretionary Line of Credit | Federal Funds Rate
Debt Instrument [Line Items]
Basis points	0.50%
4.35% Senior Notes due 2044
Debt Instrument [Line Items]
Debt Instrument, Face Amount	350,000,000	0		350,000,000
Debt Instrument, Interest Rate, Stated Percentage	4.35%			4.35%
Proceeds from Debt, Net of Issuance Costs				346,300,000
Debt Related Commitment Fees and Debt Issuance Costs				700,000
Unrealized Gain (Loss)	-1,600,000			-1,600,000
6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067
Debt Instrument [Line Items]
Debt Instrument, Face Amount	1,000,000,000	1,000,000,000
Debt Instrument, Interest Rate, Stated Percentage	6.70%
Unrealized Gain (Loss)					34,400,000
Repurchase of debt, face amount	44,300,000	54,100,000
Gains (losses) on extinguishment of debt	-4,800,000	-4,300,000
Fixed interest rate term	10 years
6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067 | Three Month LIBOR
Debt Instrument [Line Items]
Basis points	2.02%
6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067 | Net unrealized gains on forecasted transactions
Debt Instrument [Line Items]
Cash flow hedge gain reclassification from accumulated other comprehensive income to net realized gains/losses on securities	500,000	800,000	600,000
7% Notes due 2013
Debt Instrument [Line Items]
Payment of debt						$150,000,000

Income_Taxes_Components_of_Inc

Income Taxes Components of Income Tax Provision (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Current tax provision	$594.40	$460.20	$424.80
Deferred tax expense (benefit)	32	94.4	-9.4
Total income tax provision	$626.40	$554.60	$415.40

Income_Taxes_Reconciliation_of

Income Taxes Reconciliation of Provision (Benefit) for income Taxes Reported in Consolidated Statements Of Income with Tax at Statutory Rate (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Income before income taxes	$1,907.40	$1,720	$1,317.70
Tax at statutory rate	667.6	602	461.2
Dividends received deduction	-18.3	-17.6	-18.2
Exempt interest income	-13.8	-13.1	-14.7
Tax-deductible dividends	-6.5	-13.6	-11.9
Tax credits	-2.2	-2.3	0
Other items, net	-0.4	-0.8	-1
Total income tax provision	$626.40	$554.60	$415.40
Tax at statutory rate	35.00%	35.00%	35.00%
Dividends received deduction	-1.00%	-1.00%	-1.00%
Exempt interest income	-1.00%	-1.00%	-1.00%
Tax-deductible dividends	0.00%	-1.00%	-1.00%
Tax credits	0.00%	0.00%	0.00%
Other items, net	0.00%	0.00%	0.00%
Total income tax provision	33.00%	32.00%	32.00%

Income_Taxes_Components_of_Net

Income Taxes Components of Net Deferred Tax Assets (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Deferred tax assets:
Unearned premiums reserve	$378.80	$361
Investment basis differences	60.6	94.8
Non-deductible accruals	208	200.7
Loss and loss adjustment expense reserves	76.9	92
Other	7.5	14.7
Deferred tax liabilities:
Net unrealized gains on securities	-550.3	-509.9
Hedges on forecasted transactions	-0.8	-2.2
Deferred acquisition costs	-160	-156.7
Property and equipment	-100.9	-99.6
Prepaid expenses	-11.4	-14.4
Deferred gain on extinguishment of debt	-3	-4.8
Other	-4.3	-4
Net deferred tax liability	($98.90)	($28.40)

Income_Taxes_Additional_Inform

Income Taxes - Additional Information (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Taxes [Line Items]
Net taxes payable	$49.40
Net taxes recoverable		17.1
Provision (benefit) for income taxes	626.4	554.6	415.4
Interest Expense or Benefit
Income Taxes [Line Items]
Provision (benefit) for income taxes	$0	($0.20)	$0

Loss_And_Loss_Adjustment_Expen2

Loss And Loss Adjustment Expense Reserves Activity in Loss and loss Adjustment Expense Reserves (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Balance at beginning of period	$8,479.70	$7,838.40	$7,245.80
Less reinsurance recoverables on unpaid losses	1,045.90	862.1	785.7
Net balance at beginning of period	7,433.80	6,976.30	6,460.10
Incurred related to:
Current year	13,330.30	12,427.30	11,926
Prior years	-24.1	45.1	22
Total incurred	13,306.20	12,472.40	11,948
Paid related to:
Current year	8,831.50	8,095	7,895.30
Prior years	4,237	3,919.90	3,536.50
Total paid	13,068.50	12,014.90	11,431.80
Net balance at ending of period	7,671.50	7,433.80	6,976.30
Plus reinsurance recoverables on unpaid losses	1,185.90	1,045.90	862.1
Balance at ending of period	$8,857.40	$8,479.70	$7,838.40

Loss_And_Loss_Adjustment_Expen3

Loss And Loss Adjustment Expense Reserves Loss And Loss Adjustment Expense Reserves - Additional Information (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Insurance Reserves [Line Items]
Prior years	($24.10)	$45.10	$22
Accident Year 2011
Insurance Reserves [Line Items]
Unfavorable development in loss and loss adjustment expense reserves		80.00%
Accident Year 2012
Insurance Reserves [Line Items]
Unfavorable development in loss and loss adjustment expense reserves		20.00%
Commercial Lines
Insurance Reserves [Line Items]
Unfavorable development in loss and loss adjustment expense reserves		55.00%

Reinsurance_Effect_of_Reinsura

Reinsurance Effect of Reinsurance on Premiums Written and Earned (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Reinsurance Disclosures [Abstract]
Direct premiums written	$18,914.80	$17,562.80	$16,558.80
Ceded written	-260.2	-223.1	-186.1
Net premiums written	18,654.60	17,339.70	16,372.70
Direct premiums earned	18,648.40	17,317.90	16,207.60
Ceded earned	-249.9	-214.5	-189.6
Net premiums earned	$18,398.50	$17,103.40	$16,018

Reinsurance_Prepaid_Reinsuranc

Reinsurance Prepaid Reinsurance Premiums and Reinsurance Recoverables (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Prepaid reinsurance premiums	$85.30	$74.90
Percentage of Prepaid Reinsurance Premiums	100.00%	100.00%
Reinsurance Recoverables	1,231.90	1,090.20
Percentage of Reinsurance Recoverables	100.00%	100.00%
State Reinsurance Plan
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Prepaid reinsurance premiums	81.2	71.1
Percentage of Prepaid Reinsurance Premiums	95.00%	95.00%
Reinsurance Recoverables	1,180	1,005.30
Percentage of Reinsurance Recoverables	96.00%	92.00%
State Reinsurance Plan | Michigan Catastrophic Claims Association
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Prepaid reinsurance premiums	32.8	29.5
Percentage of Prepaid Reinsurance Premiums	38.00%	40.00%
Reinsurance Recoverables	1,018.80	875.9
Percentage of Reinsurance Recoverables	83.00%	80.00%
State Reinsurance Plan | Commercial Auto Insurance Procedures Plans
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Prepaid reinsurance premiums	26.5	21.1
Percentage of Prepaid Reinsurance Premiums	31.00%	28.00%
Reinsurance Recoverables	110.1	79.3
Percentage of Reinsurance Recoverables	9.00%	7.00%
State Reinsurance Plan | North Carolina Reinsurance Facility
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Prepaid reinsurance premiums	21.9	20.5
Percentage of Prepaid Reinsurance Premiums	26.00%	27.00%
Reinsurance Recoverables	51.1	50.1
Percentage of Reinsurance Recoverables	4.00%	5.00%
Non-State Reinsurance Plans
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Prepaid reinsurance premiums	4.1	3.8
Percentage of Prepaid Reinsurance Premiums	5.00%	5.00%
Reinsurance Recoverables	$51.90	$84.90
Percentage of Reinsurance Recoverables	4.00%	8.00%

Reinsurance_Additional_Informa

Reinsurance - Additional Information (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Reinsurance ceded	$322.70	$347	$230.70
State Reinsurance Plan
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Percentage of Ceded Premiums	97.00%	97.00%	98.00%
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%	77.00%	80.00%

Statutory_Financial_Informatio1

Statutory Financial Information - Additional Information (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Statutory Financial Information Disclosures [Abstract]
Consolidated statutory policyholders' surplus	$6,442.80	$5,991
Statutory net income	1,289.50	1,086.30	808.3
Consolidated statutory policyholders' surplus, net admitted assets of insurance subsidiaries and affiliate that are required to meet minimum statutory surplus requirements in such entities' states of domicile	549.2
Aggregate cash dividends paid to the parent company by subsidiaries	1,000.20
Maximum aggregate dividend amount subsidiaries could pay without prior approval from regulatory authorities	$1,346.50

Employee_Benefit_Plans_Amounts

Employee Benefit Plans Amounts Charged to Income for employees Incentive Compensation Plans (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Incentive Compensation Cash Award
Incentive Compensation Plans Expense [Line Items]
Pretax	$266.20	$234.50	$207
After Tax	173	152.4	134.6
Stock Compensation Plan
Incentive Compensation Plans Expense [Line Items]
Pretax	51.4	64.9	63.4
After Tax	$33.40	$42.20	$41.20

Employee_Benefit_Plans_Summary

Employee Benefit Plans Summary of All Employee Restricted Equity Award Activity (Detail) (Employee Restricted Equity Awards, USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Employee Restricted Equity Awards
Number of Shares
Beginning of year	9,918,575	[1],[2],[3]	11,625,981	[1],[2],[3]	12,296,847	[1]
Add (deduct):
Granted	3,542,984	[1],[4]	2,738,809	[1],[4]	2,680,229	[1],[4]
Vested	-4,228,673	[1]	-4,293,605	[1]	-3,188,111	[1]
Forfeited	-181,322	[1]	-152,610	[1]	-162,984	[1]
End of year	9,051,564	[1],[2],[3]	9,918,575	[1],[2],[3]	11,625,981	[1],[2],[3]
Weighted Average Grant Date Fair Value
Beginning of year	$20.13	[2],[3]	$17.80	[2],[3]	$16.86
Granted	$19.32	[4]	$22.73	[4]	$19.11	[4]
Vested	$16.99		$15.54		$15.23
Forfeited	$20.75		$18.28		$17.93
End of year	$21.27	[2],[3]	$20.13	[2],[3]	$17.80	[2],[3]
[1]	Includes both restricted stock units and restricted stock. Upon vesting, all units will be converted on a one-for-one basis into Progressive common shares funded from existing treasury shares. All performance-based awards are included at their target amounts.
[2]	At December 31, 2014, the number of shares included 2,647,530 performance-based awards at their target amounts. We expect 2,208,731 of these performance-based awards to vest, based upon our current estimate of the likelihood of achieving these pre-determined performance goals.
[3]	At December 31, 2014, the total unrecognized compensation cost related to unvested equity awards was $70.5 million, which includes performance-based awards at their currently estimated vesting value. This compensation expense will be recognized into the income statement over the weighted average vesting period of 2.3 years.
[4]	In 2010, we began reinvesting dividend equivalents on restricted stock units. For 2014, 2013, and 2012, the number of units "granted" shown in the table above includes 538,749, 161,077, and 440,029 of dividend equivalent units, respectively, at a weighted average grant date fair value of $0, since the dividends were factored into the grant date fair value of the original grant.

Employee_Benefit_Plans_Summary1

Employee Benefit Plans Summary of All Employee Restricted Equity Award Activity (Parenthetical) (Detail) (Employee Restricted Equity Awards, USD $)	12 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number granted units	3,542,984	[1],[2]	2,738,809	[1],[2]	2,680,229	[1],[2]
Weighted average grant date fair value	$19.32	[2]	$22.73	[2]	$19.11	[2]
Unrecognized compensation cost related to unvested equity awards	$70.50
Period of recognition of compensation expense related to unvested equity awards	2 years 3 months 15 days
Dividend Equivalent Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number granted units	538,749		161,077		440,029
Weighted average grant date fair value	$0		$0		$0
Performance Based Restricted Equity Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity awards target amount	2,647,530
Equity awards to vest	2,208,731
[1]	Includes both restricted stock units and restricted stock. Upon vesting, all units will be converted on a one-for-one basis into Progressive common shares funded from existing treasury shares. All performance-based awards are included at their target amounts.
[2]	In 2010, we began reinvesting dividend equivalents on restricted stock units. For 2014, 2013, and 2012, the number of units "granted" shown in the table above includes 538,749, 161,077, and 440,029 of dividend equivalent units, respectively, at a weighted average grant date fair value of $0, since the dividends were factored into the grant date fair value of the original grant.

Employee_Benefit_Plans_Summary2

Employee Benefit Plans Summary of all Directors' Restricted Stock Activity (Detail) (Non Employee Director Restricted Equity Awards, USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Non Employee Director Restricted Equity Awards
Number of Shares
Beginning of year	93,254	92,957	94,106
Add (deduct):
Granted	90,649	93,254	92,957
Vested	-93,254	-92,957	-94,106
Forfeited	-9,070	0	0
End of year	81,579	93,254	92,957
Weighted Average Grant Date Fair Value
Beginning of year	$26.19	$21.41	$21.80
Granted	$25.44	$26.19	$21.41
Vested	$26.19	$21.41	$21.80
Forfeited	$25.36	$0	$0
End of year	$25.45	$26.19	$21.41

Employee_Benefit_Plans_Assets_

Employee Benefit Plans Assets Held in Deferral Plan Irrevocable Grantor Trust Account (Detail) (USD $)	Dec. 31, 2014		Dec. 31, 2013
In Millions, unless otherwise specified
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Assets held in Deferral Plan Irrevocable Grantor Trust account	$207.10		$170.20
Progressive common shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Assets held in Deferral Plan Irrevocable Grantor Trust account	83.2	[1]	57.1	[1]
Other Investment Funds
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Assets held in Deferral Plan Irrevocable Grantor Trust account	$123.90	[2]	$113.10	[2]
[1]	Includes 3.6 million and 2.5 million common shares as of December 31, 2014 and 2013, respectively, to be distributed in common shares.
[2]	Amount is included in other assets on the balance sheet.

Employee_Benefit_Plans_Assets_1

Employee Benefit Plans Assets Held in Deferral Plan Irrevocable Grantor Trust Account (Parenthetical) (Detail) (Progressive common shares)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Progressive common shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common shares held in Deferral Plan Irrevocable Grantor Trust account to be distributed in-kind	3.6	2.5

Employee_Benefit_Plans_Additio

Employee Benefit Plans - Additional Information (Detail) (USD $)	12 Months Ended			1 Months Ended	12 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Feb. 28, 2009	Dec. 31, 2011	Dec. 31, 2010
Employee Benefits Disclosure [Line Items]
Employee Stock Ownership Plan Shares held	26,200,000
Postemployment benefits liability	$22.50	$24
Maximum Contractual Term Permformance-Based Awards Granted Prior to 2009	10 years
Maximum Contractual Term Performance Based Awards Granted In or After 2009	5 years
Employee Restricted Equity Awards
Employee Benefits Disclosure [Line Items]
Aggregate fair value of the restricted equity awards that vested during the period	100.9	91.8	57.7
Dividend equivalent units vested	340,949	272,617
Deferred liability awards vested			246,200
Non Employee Director Restricted Equity Awards
Employee Benefits Disclosure [Line Items]
Vesting period of grants to date	11 months
Requisite service period, minimum	6 months 1 day
Total pretax intrinsic value of options exercised and restricted stock vested	2.2	2.3	2.5
Non Employee Director Stock Option
Employee Benefits Disclosure [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period			36,237
Executive Deferred Compensation Plan
Employee Benefits Disclosure [Line Items]
Common shares reserved for issuance under executive deferred compensation plan	11,100,000
2010 Equity Incentive Plan | Employee Restricted Equity Awards
Employee Benefits Disclosure [Line Items]
Shares authorized	18,000,000
2003 Directors Equity Incentive Plan | Non Employee Director Restricted Equity Awards
Employee Benefits Disclosure [Line Items]
Shares authorized	1,400,000
Performance Based Restricted Equity Awards
Employee Benefits Disclosure [Line Items]
Number of employees, approximately	45	45	45
Performance-based awards vesting range				either vest or be forfeited in full (i.e., no partial vesting)
Performance Based Restricted Equity Awards | Insurance Operating Results | Lower Limit
Employee Benefits Disclosure [Line Items]
Performance-based awards granted vesting percentage of the award amount	0.00%	0.00%	0.00%		0.00%	0.00%
Performance Based Restricted Equity Awards | Insurance Operating Results | Upper Limit
Employee Benefits Disclosure [Line Items]
Performance-based awards granted vesting percentage of the award amount	250.00%	250.00%	200.00%		200.00%	200.00%
Performance Based Restricted Equity Awards | Investment Results | Lower Limit
Employee Benefits Disclosure [Line Items]
Performance-based awards granted vesting percentage of the award amount	0.00%	0.00%	0.00%		0.00%	0.00%
Performance Based Restricted Equity Awards | Investment Results | Upper Limit
Employee Benefits Disclosure [Line Items]
Performance-based awards granted vesting percentage of the award amount	200.00%	200.00%	200.00%		200.00%	200.00%
Other Postretirement Benefit Plans, Defined Benefit
Employee Benefits Disclosure [Line Items]
Number of employees, approximately	115
Defined Contribution Pension Plan 401k
Employee Benefits Disclosure [Line Items]
Matching contributions	$74.80	$69.90	$66.50
Defined Contribution Pension Plan 401k | Upper Limit
Employee Benefits Disclosure [Line Items]
Matching contribution to defined contribution pension plan	6.00%

Segment_Information_Operating_

Segment Information Operating Results (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Segment Reporting Information [Line Items]
Revenues	$19,391.40		$18,170.90		$17,083.90
Pretax Profit (Loss)	1,907.40		1,720		1,317.70
Underwriting Operations
Segment Reporting Information [Line Items]
Revenues	18,398.50		17,103.40		16,018
Pretax Profit (Loss)	1,410.30		1,120.10		708.9
Underwriting Operations | Personal Lines
Segment Reporting Information [Line Items]
Revenues	16,561	[1]	15,341.60	[1]	14,368.10	[1]
Pretax Profit (Loss)	1,106.40	[1]	1,016.80	[1]	628.4	[1]
Underwriting Operations | Personal Lines | Agency Channel
Segment Reporting Information [Line Items]
Revenues	9,087		8,601.50		8,103.90
Pretax Profit (Loss)	683		542.9		338.9
Underwriting Operations | Personal Lines | Direct Channel
Segment Reporting Information [Line Items]
Revenues	7,474		6,740.10		6,264.20
Pretax Profit (Loss)	423.4		473.9		289.5
Underwriting Operations | Commercial Lines
Segment Reporting Information [Line Items]
Revenues	1,837.50		1,761.60		1,649
Pretax Profit (Loss)	315.8		114.1		86.3
Underwriting Operations | Other Indemnity
Segment Reporting Information [Line Items]
Revenues	0		0.2		0.9
Pretax Profit (Loss)	-11.9		-10.8		-5.8
Fees And Other Revenues
Segment Reporting Information [Line Items]
Revenues	309.1	[2]	291.8	[2]	281.8	[2]
Service Businesses
Segment Reporting Information [Line Items]
Revenues	56		39.6		36.1
Pretax Profit (Loss)	5.1		0.8		0
Investments
Segment Reporting Information [Line Items]
Revenues	632.6	[3]	740.4	[3]	749.8	[3]
Pretax Profit (Loss)	613.7	[3]	721.6	[3]	734.4	[3]
Gains (losses) on extinguishment of debt
Segment Reporting Information [Line Items]
Revenues	-4.8		-4.3		-1.8
Pretax Profit (Loss)	-4.8		-4.3		-1.8
Interest Expense
Segment Reporting Information [Line Items]
Pretax Profit (Loss)	($116.90)		($118.20)		($123.80)
[1]	Personal auto insurance accounted for 92% of the total Personal Lines segment net premiums earned in 2014, compared to 91% in 2013 and 2012; insurance for our special lines products (e.g., motorcycles, ATVs, RVs, mobile homes, watercraft, and snowmobiles) accounted for the balance of the Personal Lines net premiums earned.
[2]	Pretax profit (loss) for fees and other revenues are allocated to operating segments.
[3]	Revenues represent recurring investment income and total net realized gains (losses) on securities; pretax profit is net of investment expenses.

Segment_Information_Operating_1

Segment Information Operating Results (Parenthetical) (Details) (Personal Lines, Personal Auto, Underwriting Operations)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Personal Lines | Personal Auto | Underwriting Operations
Segment Reporting Information [Line Items]
Personal auto insurance percentage of the total personal lines segment net premiums earned	92.00%	91.00%	91.00%

Segment_Information_Underwriti

Segment Information Underwriting Margins and Combined Ratios for our Underwriting Operations (Details) (Underwriting Operations)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting Information [Line Items]
Underwriting Margin	7.70%	6.50%	4.40%
Combined Ratio	92.30%	93.50%	95.60%
Personal Lines
Segment Reporting Information [Line Items]
Underwriting Margin	6.70%	6.60%	4.40%
Combined Ratio	93.30%	93.40%	95.60%
Personal Lines | Agency Channel
Segment Reporting Information [Line Items]
Underwriting Margin	7.50%	6.30%	4.20%
Combined Ratio	92.50%	93.70%	95.80%
Personal Lines | Direct Channel
Segment Reporting Information [Line Items]
Underwriting Margin	5.70%	7.00%	4.60%
Combined Ratio	94.30%	93.00%	95.40%
Commercial Lines
Segment Reporting Information [Line Items]
Underwriting Margin	17.20%	6.50%	5.20%
Combined Ratio	82.80%	93.50%	94.80%

Segment_Information_Additional

Segment Information - Additional Information (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting Information [Line Items]
Net premiums earned	$18,398.50	$17,103.40	$16,018
Depreciation	97.1	101.3	94.4
Underwriting Operations | Personal Lines | Agency Channel | Lower Limit
Segment Reporting Information [Line Items]
Independent insurance agencies and brokerages	35,000
Australia
Segment Reporting Information [Line Items]
Net premiums earned	$17.10	$13	$7.10

Other_Comprehensive_Income_Com

Other Comprehensive Income Components of Other Comprehensive Income (Loss) Including Reclassification Adjustments by Income Statement (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accumulated Other Comprehensive Income (Loss), before Tax [Roll Forward]
Pre tax total accumulated other comprehensive income, beginning balance	$1,464,100,000	$1,340,000,000	$1,065,400,000
Investment securities, pre tax	362,100,000	368,200,000	488,000,000
Net non-credit related OTTI losses, adjusted for valuation changes, pre tax	0	400,000	7,900,000
Forecasted transactions, pre tax	-1,600,000	0	0
Foreign currently translation adjustement, pre tax	-1,300,000	-2,500,000	600,000
Total other comprehensive income (loss) before reclassifications, pre tax	359,200,000	366,100,000	496,500,000
Total reclassification adjustment for amounts realized in net income, pre tax	249,300,000	242,000,000	221,900,000
Total other comprehensive income (loss), pre tax	109,900,000	124,100,000	274,600,000
Pre tax total accumulated other comprehensive income, ending balance	1,574,000,000	1,464,100,000	1,340,000,000
Accumulated Other Comprehensive Income (Loss), Tax [Roll Forward]
Accumulated other comprehensive income loss tax (provision) benefit, beginning balance	-512,400,000	-469,000,000	-372,900,000
Investment securities, Total tax (provision) benefit	-126,700,000	-128,900,000	-170,800,000
Net non-credit related OTTI losses, adjusted for valuation changes Total tax (provision) benefit	0	-100,000	-2,800,000
Forecasted transactions, Total tax (provision) benefit	600,000	0	0
Foreign currency traslation adjustment, Total tax (provision) benefit	400,000	900,000	-200,000
Total other comprehensive Income (loss) before reclassifications, Total tax (provision) benefit	-125,700,000	-128,100,000	-173,800,000
Total reclassification adjustment for amounts realized in net income, Total tax (provision) benefit	-87,200,000	-84,700,000	-77,700,000
Total other comprehensive income (loss), Total tax (provision) benefit	-38,500,000	-43,400,000	-96,100,000
Accumulated other comprehensive income loss tax (provision) benefit, ending balance	-550,900,000	-512,400,000	-469,000,000
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
After tax total other accumulated comprehensive income, beginning balance	951,700,000	871,000,000	692,500,000
Investment securities, after tax	235,400,000	239,300,000	317,200,000
Net non-credit related OTTI losses, adjusted for valuation changes, after tax	0	300,000	5,100,000
Forecasted transactions, after tax	-1,000,000	0	0
Foreign currency translation adjustment, after tax	-900,000	-1,600,000	400,000
Total other comprehensive income (loss), before reclassifications, after tax	233,500,000	238,000,000	322,700,000
Total reclassification adjustment for amounts realized in net income, after tax	162,100,000	157,300,000	144,200,000
Other comprehensive income (loss)	71,400,000	80,700,000	178,500,000
After tax total other accumulated comprehensive income, ending balance	1,023,100,000	951,700,000	871,000,000
Net impairment losses recognized in earnings	-7,900,000	-6,100,000	-8,000,000
Net realized gains (losses) on securities	232,100,000	324,500,000	314,800,000
Interest expense	116,900,000	118,200,000	123,800,000
Net unrealized gains (losses) on securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
After tax total other accumulated comprehensive income, beginning balance	947,000,000	862,700,000	682,800,000
Investment securities, after tax	235,400,000	239,300,000	317,200,000
Net non-credit related OTTI losses, adjusted for valuation changes, after tax	0	300,000	5,100,000
Forecasted transactions, after tax	0	0	0
Foreign currency translation adjustment, after tax	0	0	0
Total other comprehensive income (loss), before reclassifications, after tax	235,400,000	239,600,000	322,300,000
Total reclassification adjustment for amounts realized in net income, after tax	160,500,000	155,300,000	142,400,000
Other comprehensive income (loss)	74,900,000	84,300,000	179,900,000
After tax total other accumulated comprehensive income, ending balance	1,021,900,000	947,000,000	862,700,000
Net unrealized gains on forecasted transactions
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
After tax total other accumulated comprehensive income, beginning balance	4,100,000	6,100,000	7,900,000
Investment securities, after tax	0	0	0
Net non-credit related OTTI losses, adjusted for valuation changes, after tax	0	0	0
Forecasted transactions, after tax	-1,000,000	0	0
Foreign currency translation adjustment, after tax	0	0	0
Total other comprehensive income (loss), before reclassifications, after tax	-1,000,000	0	0
Total reclassification adjustment for amounts realized in net income, after tax	1,600,000	2,000,000	1,800,000
Other comprehensive income (loss)	-2,600,000	-2,000,000	-1,800,000
After tax total other accumulated comprehensive income, ending balance	1,500,000	4,100,000	6,100,000
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
After tax total other accumulated comprehensive income, beginning balance	600,000	2,200,000	1,800,000
Investment securities, after tax	0	0	0
Net non-credit related OTTI losses, adjusted for valuation changes, after tax	0	0	0
Forecasted transactions, after tax	0	0	0
Foreign currency translation adjustment, after tax	-900,000	-1,600,000	400,000
Total other comprehensive income (loss), before reclassifications, after tax	-900,000	-1,600,000	400,000
Total reclassification adjustment for amounts realized in net income, after tax	0	0	0
Other comprehensive income (loss)	-900,000	-1,600,000	400,000
After tax total other accumulated comprehensive income, ending balance	-300,000	600,000	2,200,000
Reclassification out of Accumulated Other Comprehensive Income | Accumulated other comprehesnive income pretax
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Net impairment losses recognized in earnings	-7,700,000	-5,700,000	-400,000
Net realized gains (losses) on securities	255,000,000	245,500,000	220,100,000
Interest expense	2,000,000	2,200,000	2,200,000
Reclassification out of Accumulated Other Comprehensive Income | Accumulated other comprehensive income tax
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Net impairment losses recognized in earnings	2,700,000	2,000,000	100,000
Net realized gains (losses) on securities	-89,200,000	-86,000,000	-77,000,000
Interest expense	-700,000	-700,000	-800,000
Reclassification out of Accumulated Other Comprehensive Income | Accumulated other comprehensive income after tax
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Net impairment losses recognized in earnings	-5,000,000	-3,700,000	-300,000
Net realized gains (losses) on securities	165,800,000	159,500,000	143,100,000
Interest expense	1,300,000	1,500,000	1,400,000
Reclassification out of Accumulated Other Comprehensive Income | Net unrealized gains (losses) on securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Net impairment losses recognized in earnings	-5,000,000	-3,700,000	-300,000
Net realized gains (losses) on securities	165,500,000	159,000,000	142,700,000
Interest expense	0	0	0
Reclassification out of Accumulated Other Comprehensive Income | Net unrealized gains on forecasted transactions
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Net impairment losses recognized in earnings	0	0	0
Net realized gains (losses) on securities	300,000	500,000	400,000
Interest expense	1,300,000	1,500,000	1,400,000
Reclassification out of Accumulated Other Comprehensive Income | Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Net impairment losses recognized in earnings	0	0	0
Net realized gains (losses) on securities	0	0	0
Interest expense	$0	$0	$0

Other_Comprehensive_Income_Com1

Other Comprehensive Income Components of Other Comprehensive Income (Loss) Including Reclassification Adjustments by Income Statement (Parenthetical) (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Pre Tax
Components Of Other Comprehensive Income Loss [Line Items]
Net unrealized gains on forecasted transactions, expected to reclassify into income within the next 12 months	$2
6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067 | Net unrealized gains on forecasted transactions
Components Of Other Comprehensive Income Loss [Line Items]
Cash flow hedge gain reclassification from accumulated other comprehensive income to net realized gains/losses on securities	$0.50	$0.80	$0.60

Commitments_and_Contingencies_1

Commitments and Contingencies Minimum Commitments under Noncancelable Operating Lease Agreements (Detail) (USD $)	Dec. 31, 2014
In Millions, unless otherwise specified
Commitments and Contingencies Disclosure [Abstract]
2015	$46.20
2016	43.7
2017	37.2
2018	27.1
2019	16.4
Thereafter	4.4
Total	$175

Commitments_and_Contingencies_2

Commitments and Contingencies Expenses Incurred for Leases (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Commitments and Contingencies Disclosure [Abstract]
Expense	$63.40	$64.60	$71.90

Commitments_and_Contingencies_3

Commitments and Contingencies - Additional Information (Detail) (USD $)	Dec. 31, 2014
In Millions, unless otherwise specified
Commitments and Contingencies Disclosure [Abstract]
Minimum commitment under noncancelable purchase obligations	$493.50

Dividends_Dividends_Details

Dividends Dividends (Details) (USD $)	1 Months Ended			0 Months Ended
In Millions, except Per Share data, unless otherwise specified	Feb. 26, 2014	Feb. 28, 2013	Nov. 30, 2012	Feb. 13, 2015
Annual variable dividend
Common Stock, Dividends, Per Share, Cash Paid	$0.49	$0.28
Payments of Ordinary Dividends, Common Stock	$293.90	$172
Special dividend
Common Stock, Dividends, Per Share, Cash Paid	$1		$1
Payments of Ordinary Dividends, Common Stock	596.3		604.7
Subsequent Event | Annual variable dividend
Common Stock, Dividends, Per Share, Cash Paid				$0.69
Payments of Ordinary Dividends, Common Stock				$404.10

DividendsAdditional_Informatio

Dividends-Additional Information (Details)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Dividends [Abstract]
Target percentage used to determine annual variable dividend	33.33%
Gainshare factor used to determine annual variable dividend range, minimum	0
Gainshare factor used to determine annual variable dividend range, maximum	2
Gainshare factor used to determine annual variable dividend	1.32	1.21	1.12

Subsequent_Event_Subsequent_Ev

Subsequent Event Subsequent Event - Additional Information (Details) (Subsequent Event, 3.70% Senior Notes due 2045, USD $)	1 Months Ended
	Jan. 26, 2015
Subsequent Event | 3.70% Senior Notes due 2045
Debt Instrument [Line Items]
Debt Instrument, Issuance Date	26-Jan-15
Debt Instrument, Face Amount	$400,000,000
Debt Instrument, Interest Rate, Stated Percentage	3.70%
Proceeds from Debt, Net of Issuance Costs	394,900,000
Debt Related Commitment Fees and Debt Issuance Costs	800,000
Unrealized Gain (Loss)	($12,900,000)