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 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	$ 7.7
Common Stock, Dividends, Per Share, Declared	$ 0.00
Preferred Stock, Dividends Per Share, Declared								$ 27.024
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	$ 2,350.6					2,350.6
Treasury shares purchased				(1.4)	(3.3)	(74.0)
Cash dividends declared on common shares ($0.10, $0, $0.30, and $0 per share)						0.0
Cash dividends declared on Serial Preferred Shares, Series B ($26.875, $27.024, $53.750, and $27.024 per share)						(13.5)
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				2.8	(2.8)
Amortization of equity-based compensation					53.3
Adjustment to carrying amount of redeemable noncontrolling interest	(3.1)				7.8
Attributable to noncontrolling interest	5.0						1.6
Other comprehensive income							(243.0)
Other, net						2.0
Balance, End of period at Sep. 30, 2018	11,858.8		493.9	583.1	1,443.4	9,602.1	(263.7)
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	$ 3.4
Common Stock, Dividends, Per Share, Declared	$ 0.00
Preferred Stock, Dividends Per Share, Declared								27.024
Balance, Beginning of period at Jun. 30, 2018			493.9	582.5	1,425.9	8,720.4	(221.9)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to Progressive	$ 928.4					928.4
Treasury shares purchased				(0.7)	(1.6)	(37.0)
Cash dividends declared on common shares ($0.10, $0, $0.30, and $0 per share)						0.0
Cash dividends declared on Serial Preferred Shares, Series B ($26.875, $27.024, $53.750, and $27.024 per share)						(13.5)
Reinvested dividends on restricted stock units					0.0	0.0
Issuance of Serial Preferred Shares, Series B			0.0
Net restricted equity awards issued/vested				1.3	(1.3)
Amortization of equity-based compensation					15.8
Adjustment to carrying amount of redeemable noncontrolling interest					4.6
Attributable to noncontrolling interest	0.4						(3.0)
Other comprehensive income							(38.8)
Other, net						3.8
Balance, End of period at Sep. 30, 2018	$ 11,858.8		493.9	583.1	1,443.4	9,602.1	(263.7)
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
Common Stock, Dividends, Per Share, Declared	$ 0.30
Preferred Stock, Dividends Per Share, Declared								$ 53.750
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	2,899.5					2,899.5
Treasury shares purchased				(1.2)	(3.1)	(83.8)
Cash dividends declared on common shares ($0.10, $0, $0.30, and $0 per share)						(175.0)
Cash dividends declared on Serial Preferred Shares, Series B ($26.875, $27.024, $53.750, and $27.024 per share)						(26.8)
Reinvested dividends on restricted stock units					1.3	(1.3)
Issuance of Serial Preferred Shares, Series B			0.0
Net restricted equity awards issued/vested				2.6	(2.6)
Amortization of equity-based compensation					64.7
Adjustment to carrying amount of redeemable noncontrolling interest	0.2				(0.2)
Attributable to noncontrolling interest	(5.8)						(5.8)
Other comprehensive income							637.2
Other, net						(4.0)
Balance, End of period at Sep. 30, 2019	$ 14,123.3		493.9	584.6	1,539.1	10,995.2	510.5
Common Stock, Dividends, Per Share, Declared	$ 0.10
Preferred Stock, Dividends Per Share, Declared								26.875
Balance, Beginning of period at Jun. 30, 2019			493.9	584.1	1,523.3	10,276.4	453.1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to Progressive	$ 841.7					841.7
Treasury shares purchased				(0.7)	(2.0)	(57.0)
Cash dividends declared on common shares ($0.10, $0, $0.30, and $0 per share)						(58.4)
Cash dividends declared on Serial Preferred Shares, Series B ($26.875, $27.024, $53.750, and $27.024 per share)						(13.4)
Reinvested dividends on restricted stock units					0.4	(0.4)
Issuance of Serial Preferred Shares, Series B			0.0
Net restricted equity awards issued/vested				1.2	(1.2)
Amortization of equity-based compensation					18.6
Adjustment to carrying amount of redeemable noncontrolling interest					0.0
Attributable to noncontrolling interest	(0.9)						(0.9)
Other comprehensive income							58.3
Other, net						6.3
Balance, End of period at Sep. 30, 2019	$ 14,123.3		$ 493.9	$ 584.6	$ 1,539.1	10,995.2	510.5
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