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
Common Stock, Dividends, Per Share, Declared	$ 0.30
Preferred Stock, Dividends Per Share, Declared								$ 53.750
Balance, Beginning of period at Dec. 31, 2019			$ 493.9	$ 584.6	$ 1,573.4	$ 10,679.6	$ 341.7
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 4,020.3					4,020.3
Treasury shares purchased				(0.9)	(2.5)	(71.1)
Cash dividends declared on common shares ($0.10, $0.10, $0.30, and $0.30 per share)						(175.3)
Cash dividends declared on Serial Preferred Shares, Series B ($26.875, $26.875, $26.875, and $53.750 per share)						(26.8)
Reinvested dividends on restricted stock units					1.1	(1.1)
Net restricted equity awards issued/vested				1.9	(1.9)
Amortization of equity-based compensation					61.9
Adjustment to carrying amount of redeemable noncontrolling interest					(2.6)
Attributable to noncontrolling interest							2.7
Other comprehensive income (loss)	606.2						606.2
Other, net						2.1
Balance, End of period at Sep. 30, 2020	$ 18,087.2		493.9	585.6	1,629.4	14,427.7	950.6
Common Stock, Dividends, Per Share, Declared	$ 0.10
Preferred Stock, Dividends Per Share, Declared								26.875
Balance, Beginning of period at Jun. 30, 2020			493.9	585.4	1,614.5	13,001.8	975.0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 1,530.8					1,530.8
Treasury shares purchased				(0.5)	(1.5)	(43.4)
Cash dividends declared on common shares ($0.10, $0.10, $0.30, and $0.30 per share)						(58.5)
Cash dividends declared on Serial Preferred Shares, Series B ($26.875, $26.875, $26.875, and $53.750 per share)						(13.4)
Reinvested dividends on restricted stock units					0.4	(0.4)
Net restricted equity awards issued/vested				0.7	(0.7)
Amortization of equity-based compensation					16.7
Adjustment to carrying amount of redeemable noncontrolling interest					0.0
Attributable to noncontrolling interest							0.0
Other comprehensive income (loss)	(24.4)						(24.4)
Other, net						10.8
Balance, End of period at Sep. 30, 2020	$ 18,087.2		493.9	585.6	1,629.4	14,427.7	950.6
Preferred Stock, No Par Value								$ 0
Preferred Stock, Shares Authorized (shares)		20,000,000.0						500,000	5,000,000.0
Preferred Stock, Shares Issued (shares)								500,000	0
Common Shares, par value (USD per share)	$ 1.00
Preferred Stock, No Par Value								$ 0
Preferred Stock, Shares Authorized (shares)		20,000,000.0						500,000
Preferred Stock, Shares Issued (shares)								500,000
Common Shares, par value (USD per share)	1.00
Common Stock, Dividends, Per Share, Declared	$ 0.30
Preferred Stock, Dividends Per Share, Declared								$ 26.875
Balance, Beginning of period at Dec. 31, 2020	$ 17,038.6		493.9	585.2	1,672.9	13,354.9	931.7
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	2,388.6					2,388.6
Treasury shares purchased				(1.8)	(5.3)	(160.1)
Cash dividends declared on common shares ($0.10, $0.10, $0.30, and $0.30 per share)						(175.2)
Cash dividends declared on Serial Preferred Shares, Series B ($26.875, $26.875, $26.875, and $53.750 per share)						(13.4)
Reinvested dividends on restricted stock units					1.2	(1.2)
Net restricted equity awards issued/vested				1.6	(1.6)
Amortization of equity-based compensation					68.7
Adjustment to carrying amount of redeemable noncontrolling interest					0.0
Attributable to noncontrolling interest							0.0
Other comprehensive income (loss)	(578.4)						(578.4)
Other, net						(3.6)
Balance, End of period at Sep. 30, 2021	$ 18,558.1		493.9	585.0	1,735.9	15,390.0	353.3
Common Stock, Dividends, Per Share, Declared	$ 0.10
Preferred Stock, Dividends Per Share, Declared								26.875
Balance, Beginning of period at Jun. 30, 2021			493.9	585.2	1,712.3	15,401.0	483.2
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 118.5					118.5
Treasury shares purchased				(0.7)	(2.3)	(68.8)
Cash dividends declared on common shares ($0.10, $0.10, $0.30, and $0.30 per share)						(58.4)
Cash dividends declared on Serial Preferred Shares, Series B ($26.875, $26.875, $26.875, and $53.750 per share)						(13.4)
Reinvested dividends on restricted stock units					0.4	(0.4)
Net restricted equity awards issued/vested				0.5	(0.5)
Amortization of equity-based compensation					26.0
Adjustment to carrying amount of redeemable noncontrolling interest					0.0
Attributable to noncontrolling interest							0.0
Other comprehensive income (loss)	(129.9)						(129.9)
Other, net						11.5
Balance, End of period at Sep. 30, 2021	$ 18,558.1		$ 493.9	$ 585.0	$ 1,735.9	$ 15,390.0	$ 353.3
Preferred Stock, No Par Value								$ 0
Preferred Stock, Shares Authorized (shares)		20,000,000.0						500,000	5,000,000.0
Preferred Stock, Shares Issued (shares)								500,000	0
Common Shares, par value (USD per share)	$ 1.00