Consolidated Statements of Comprehensive Income - USD ($) shares in Millions, $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Income Statement [Abstract]
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net		$ 61.6	$ 13.6	$ 61.8	$ 23.2
Revenues
Net premiums earned		$ 5,723.4	5,070.6	$ 16,602.6	14,732.7
Period over prior year period percent change in net premiums earned		13.00%		13.00%
Investment income		$ 119.3	117.5	$ 352.7	335.9
Period over prior year period percent change in investment income		2.00%		5.00%
Net realized gains (losses) on securities:
Period over prior year period percent change in net premium losses recognized in earnings		353.00%		166.00%
Net realized gains (losses) on securities		$ 40.9	(2.2)	$ 90.8	116.4
Period over prior year period percent change in net realized gains (losses) on securities				(22.00%)
Total net realized gains (losses) on securities		$ (20.7)	(15.8)	$ 29.0	93.2
Period over prior year period percent change in total net realized gains (losses) on securities		31.00%		(69.00%)
Fees and other revenues		$ 86.8	79.3	$ 248.2	227.9
Period over prior year period percent change in fees and other revenues		9.00%		9.00%
Service revenues		$ 26.2	23.1	$ 77.7	63.6
Period over prior year period percent change in service revenues		13.00%		22.00%
Gains (losses) on extinguishment of debt		$ 0.0	(0.9)	$ 1.6	(0.9)
PercentIncrease(Decrease)GainLossonExtingiushmentofDebt		(100.00%)		(278.00%)
Total revenues		$ 5,935.0	5,273.8	$ 17,311.8	15,452.4
Period over prior year period percent change in total revenues		13.00%		12.00%
Expenses
Losses and loss adjustment expenses		$ 4,398.2	3,654.3	$ 12,554.6	10,640.1
Period over prior year period percent change in losses and loss adjustment expenses		20.00%		18.00%
Policy acquisition costs		$ 475.4	423.2	$ 1,374.6	1,219.9
Period over prior year period percent change in policy acquisition costs		12.00%		13.00%
Other underwriting expenses		$ 739.6	707.5	$ 2,262.2	2,020.3
Period over prior year period percent change in other underwriting expenses		5.00%		12.00%
Investment expenses		$ 4.8	4.9	$ 14.9	15.9
Period over prior year period percent change in investment expenses		(2.00%)		(6.00%)
Service expenses		$ 23.2	20.4	$ 68.5	56.8
Period over prior year period percent change in service expenses		14.00%		21.00%
Interest expense		$ 35.3	34.5	$ 103.8	101.9
Period over prior year period percent change in interest expense		2.00%		2.00%
Total expenses		$ 5,676.5	4,844.8	$ 16,378.6	14,054.9
Period over prior year period percent change in total expenses		17.00%		17.00%
Net Income
Income before income taxes		$ 258.5	429.0	$ 933.2	1,397.5
Period over prior year period percent change in income before income taxes		(40.00%)		(33.00%)
Provision for income taxes		$ 53.0	142.5	$ 274.1	446.9
Period over prior year period percent change in provision for income taxes		(63.00%)		(39.00%)
Net income		$ 205.5	286.5	$ 659.1	950.6
Period over prior year period percent change in net income		(28.00%)		(31.00%)
Net income (loss) attributable to noncontrolling interest (NCI), net of tax		$ 6.8	8.2	$ 11.3	13.4
Period over prior year period percent change in net income (loss) attributable to noncontrolling interest, net of tax		(17.00%)		(16.00%)
Net income attributable to Progressive		$ 198.7	278.3	$ 647.8	937.2
Period over prior year period percent change in net income attributable to Progressive		(29.00%)		(31.00%)
Other Comprehensive Income (Loss), Net of Tax
Total net unrealized gains (losses) on securities		$ 87.1	(130.1)	$ 248.2	(244.5)
Period over prior year period percent change in total net unrealized gains (losses) on securities		(167.00%)		(202.00%)
Net unrealized losses on forecasted transactions		$ (0.3)	(0.4)	$ (0.9)	(9.4)
Period over prior year period percent change in net unrealized gains on forecasted transactions		(25.00%)		(90.00%)
Foreign currency translation adjustment		$ 0.3	(0.7)	$ 0.7	(1.2)
Period over prior year period percent change in foreign currency translation adjustment		(143.00%)		(158.00%)
Other comprehensive income (loss)		$ 87.1	(131.2)	$ 248.0	(255.1)
Period over prior year period percent change in other comprehensive income		(166.00%)		(197.00%)
Other comprehensive (income) loss attributable to NCI		$ 1.2	(1.6)	$ (2.3)	1.2
Period over prior year period changein Comprehensive (income) loss attributable to NCI, net of tax		(175.00%)		(292.00%)
Comprehensive income attributable to Progressive		$ 287.0	$ 145.5	$ 893.5	$ 683.3
Period over prior year period percent change in comprehensive income		97.00%		31.00%
Computation of Per Share Earnings Attributable to Progressive
Average shares outstanding - Basic		581.5	585.2	582.4	586.1
Period over prior year period percent change in average shares outstanding - basic		(1.00%)		(1.00%)
Net effect of dilutive stock-based compensation		3.1	3.9	3.2	3.7
Period over prior year period percent change in net effect of dilutive stock-based compensation		(21.00%)		(14.00%)
Total equivalent shares - Diluted		584.6	589.1	585.6	589.8
Period over prior year period percent change in total equivalent shares - diluted		(1.00%)		(1.00%)
Basic: Earnings per share		$ 0.34	$ 0.48	$ 1.11	$ 1.60
Period over prior year period percent change in basic: net income per share		(28.00%)		(30.00%)
Diluted: Earnings per share		$ 0.34	0.47	$ 1.11	1.59
Period over prior year period percent change in diluted: net income per share		(28.00%)		(30.00%)
Dividends declared per share1	[1]	$ 0	$ 0	$ 0	$ 0

[1] Progressive maintains an annual dividend program. See Note 8 - Dividends for further discussion.