Consolidated Statements of Changes in Shareholders' Equity Statement - USD ($) $ in Millions	Total	Serial Preferred Stock	Preferred Shares, No Par Value	Common Shares, $1.00 Par Value	Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss) Attributable to Progressive	Series B Preferred Stock	Series B Preferred Stock Serial Preferred Stock	Voting Preference Shares
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of change in accounting principle	$ 1,300.2
Reclassification of disproportionate tax effects	$ 4.3
Common Stock, Dividends, Per Share, Declared	$ 0.00
Preferred Stock, Dividends Per Share, Declared									$ 0.000
Balance, Beginning of period at Dec. 31, 2017			$ 0.0	$ 581.7	$ 1,389.2	$ 6,031.7	$ 1,282.2
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to Progressive	$ 1,422.2					1,422.2
Treasury shares purchased				(0.7)	(1.7)	(37.0)
Cash dividends declared on common shares ($0.10, $0, $0.20, and $0 per share)						0.0
Cash dividends declared on Serial Preferred Shares, Series B ($0, $0, $26.875, and $0 per share)						0.0
Reinvested dividends on restricted stock units					(0.8)	0.8
Issuance of Serial Preferred Shares, Series B			493.9
Net restricted equity awards issued/vested				1.5	(1.5)
Amortization of equity-based compensation					37.5
Adjustment to carrying amount of redeemable noncontrolling interest	(3.2)				3.2
Attributable to noncontrolling interest	4.6						4.6
Other comprehensive income							(204.2)
Other, net						(1.8)
Balance, End of period at Jun. 30, 2018	11,000.8		493.9	582.5	1,425.9	8,720.4	(221.9)
Balance, Beginning of period at Dec. 31, 2017			0.0	581.7	1,389.2	6,031.7	1,282.2
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adjustment to carrying amount of redeemable noncontrolling interest	(2.8)
Attributable to noncontrolling interest	3.3
Balance, End of period at Dec. 31, 2018	$ 10,821.8		493.9	583.2	1,479.0	8,386.6	(120.9)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Reclassification of disproportionate tax effects | Accounting Standards Update 2018-02						4.3	(4.3)
Common Stock, Dividends, Per Share, Declared	$ 0.00
Preferred Stock, Dividends Per Share, Declared									0.000
Balance, Beginning of period at Mar. 31, 2018			493.9	582.4	1,401.6	8,017.9	(172.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to Progressive	$ 704.2					704.2
Treasury shares purchased				0.0	(0.1)	(2.1)
Cash dividends declared on common shares ($0.10, $0, $0.20, and $0 per share)						0.0
Cash dividends declared on Serial Preferred Shares, Series B ($0, $0, $26.875, and $0 per share)						0.0
Reinvested dividends on restricted stock units					(0.3)	0.3
Issuance of Serial Preferred Shares, Series B			0.0
Net restricted equity awards issued/vested				0.1	(0.1)
Amortization of equity-based compensation					20.3
Adjustment to carrying amount of redeemable noncontrolling interest					4.5
Attributable to noncontrolling interest	0.6						0.6
Other comprehensive income							(49.9)
Other, net						0.1
Balance, End of period at Jun. 30, 2018	$ 11,000.8		493.9	582.5	1,425.9	8,720.4	(221.9)
Preferred Stock, No Par Value									$ 0
Preferred Stock, Shares Authorized (shares)		20,000,000							500,000.0	5,000,000.0
Preferred Stock, Shares Issued (shares)									500,000.0	0
Common Shares, par value (USD per share)	$ 1.00
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of change in accounting principle | Accounting Standards Update 2016-01						0.0	0.0
Reclassification of disproportionate tax effects | Accounting Standards Update 2018-02						0.0	0.0
Preferred Stock, No Par Value									$ 0
Preferred Stock, Shares Authorized (shares)		20,000,000							500,000.0
Preferred Stock, Shares Issued (shares)									500,000.0
Common Shares, par value (USD per share)	$ 1.00
Preferred Stock, Dividends Per Share, Declared								$ 26.875
Balance, Beginning of period at Dec. 31, 2018	$ 10,821.8		493.9	583.2	1,479.0	8,386.6	(120.9)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends declared on Serial Preferred Shares, Series B ($0, $0, $26.875, and $0 per share)								$ (13.4)
Balance, End of period at Mar. 31, 2019			493.9	584.0	1,496.6	9,358.1	178.1
Common Stock, Dividends, Per Share, Declared	$ 0.20
Preferred Stock, Dividends Per Share, Declared									$ 26.875
Balance, Beginning of period at Dec. 31, 2018	$ 10,821.8		493.9	583.2	1,479.0	8,386.6	(120.9)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to Progressive	2,057.8					2,057.8
Treasury shares purchased				(0.5)	(1.1)	(26.8)
Cash dividends declared on common shares ($0.10, $0, $0.20, and $0 per share)						(116.6)
Cash dividends declared on Serial Preferred Shares, Series B ($0, $0, $26.875, and $0 per share)						(13.4)
Reinvested dividends on restricted stock units					0.9	(0.9)
Issuance of Serial Preferred Shares, Series B			0.0
Net restricted equity awards issued/vested				1.4	(1.4)
Amortization of equity-based compensation					46.1
Adjustment to carrying amount of redeemable noncontrolling interest	0.2				(0.2)
Attributable to noncontrolling interest	(4.9)						(4.9)
Other comprehensive income							578.9
Other, net						(10.3)
Balance, End of period at Jun. 30, 2019	$ 13,330.8		493.9	584.1	1,523.3	10,276.4	453.1
Common Stock, Dividends, Per Share, Declared	$ 0.10
Preferred Stock, Dividends Per Share, Declared									0.000
Balance, Beginning of period at Mar. 31, 2019			493.9	584.0	1,496.6	9,358.1	178.1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to Progressive	$ 979.4					979.4
Treasury shares purchased				(0.1)	0.0	(2.2)
Cash dividends declared on common shares ($0.10, $0, $0.20, and $0 per share)						(58.3)
Cash dividends declared on Serial Preferred Shares, Series B ($0, $0, $26.875, and $0 per share)						0.0
Reinvested dividends on restricted stock units					0.6	(0.6)
Issuance of Serial Preferred Shares, Series B			0.0
Net restricted equity awards issued/vested				0.2	(0.2)
Amortization of equity-based compensation					26.5
Adjustment to carrying amount of redeemable noncontrolling interest					(0.2)
Attributable to noncontrolling interest	(2.6)						(2.6)
Other comprehensive income							277.6
Other, net						0.0
Balance, End of period at Jun. 30, 2019	$ 13,330.8		$ 493.9	$ 584.1	$ 1,523.3	10,276.4	453.1
Preferred Stock, No Par Value									$ 0
Preferred Stock, Shares Authorized (shares)		20,000,000							500,000.0	5,000,000.0
Preferred Stock, Shares Issued (shares)									500,000.0	0
Common Shares, par value (USD per share)	$ 1.00
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of change in accounting principle | Accounting Standards Update 2016-01						0.0	0.0
Reclassification of disproportionate tax effects | Accounting Standards Update 2018-02						$ 0.0	$ 0.0