Employee Benefit Plans (Details) $ / shares in Units, $ in Millions		12 Months Ended
		Dec. 31, 2023 USD ($) plan $ / shares shares	Dec. 31, 2022 USD ($) $ / shares shares	Dec. 31, 2021 USD ($) $ / shares shares	Dec. 31, 2020 USD ($) $ / shares shares	Dec. 31, 2018 USD ($) shares	Dec. 31, 2015 USD ($) shares
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Securities at Net Asset Value		$ 6.5	$ 3.1
ORI 401(k) Savings and Profit Sharing Plan, unallocated shares | shares		3,955,122
Employee savings and stock ownership plan, number of allocated shares | shares		19,362,130
Employee savings and stock ownership plan, number of allocated shares to employees | shares		15,407,008
stock acquired during period value employee stock ownership plan					$ 50.0	$ 50.0	$ 34.0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		$ 504.0
Fair value of net assets available for plan benefits at end of year		514.0	504.0
Net pretax amount recognized		(10.8)	$ (86.6)	$ (101.9)
Estimated future cash contributions next year		$ 0.0
Share contractual period		10 years
Expected volatility		23.00%	22.00%	20.00%
Expected dividends		4.66%	4.32%	4.76%
Expected term (in years)		6 years	6 years	7 years
Risk-free rate		3.69%	2.68%	1.21%
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Number of new common stock shares available under the 2020 Incentive Compensation Plan | shares		20,000,000.0
Maximum Number of Common Stock Shares Available Under 2016 Stock Option Plan | shares		4,700,000
Maximum number of common shares available under the 2022 Incentive Compensation Plan | shares		17,700,000
Share-based compensation expense		$ 19.5	$ 9.0	$ 3.2
Income tax benefit		$ 4.1	$ 1.8	$ 0.6
Award vesting rate, within one year of grant date		3 years
Award vesting rate, within one year of grant date		10.00%
Award vesting rate, between year one and year two		15.00%
Award vesting rate, between year two and year three		20.00%
Award vesting rate, between year three and year four		25.00%
Award vesting rate, between year four and year five		30.00%
Options, outstanding at beginning of year | shares		9,619,004	8,344,470	9,494,651
Granted | shares		2,990,000	2,660,000	2,216,250
Exercised | shares		1,694,106	1,285,783	3,259,273
Forfeited and canceled | shares		44,684	99,683	107,158
Options, outstanding at end of year | shares		10,870,214	9,619,004	8,344,470	9,494,651
Exercisable at end of year | shares		4,790,571	4,562,063	4,652,951
Granted, Weighted Average Exercise Price | $ / shares		$ 25.22	$ 23.28	$ 21.30
Exercised, Weighted Average Exercise Price | $ / shares		19.49	18.94	17.28
Forfeited and canceled, Weighted Average Exercise Price | $ / shares		22.04	19.78	18.32
Options, outstanding, weighted average exercise price | $ / shares		22.10	20.68	19.57	$ 18.36
Exercisable at end of year, Weighted Average Exercise Price | $ / shares		20.31	19.53	19.22
Weighted average fair value of options granted during the year | $ / shares	[1]	$ 3.76	$ 3.31	$ 1.86
Total unrecognized compensation cost		$ 29.7
Unrecognized stock compensation costs, weighted average remaining contractual term		3 years
Cash received from stock option exercise		$ 33.0	$ 24.3	$ 56.3
Intrinsic value of stock options exercised		17.5	7.9	24.2
Actual tax benefit realized for tax deductions from stock options exercised		$ 3.6	$ 1.6	$ 5.0
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number | shares		1,257,116	659,874	33,539
Granted | shares		823,907	644,356
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period | shares		(225,289)	(16,901)
Forfeited and canceled | shares		(1,376)	(1,120)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value | $ / shares		$ 24.67	$ 23.70	$ 21.32
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value | $ / shares		25.15	23.76
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value | $ / shares		23.60	21.20
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value | $ / shares		$ 25.05	$ 22.34
Defined contribution plan, one-time cost		$ 10.7
Employees Savings and Stock Ownership Plan [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Defined contribution plan, cost recognized		65.8	$ 77.8	$ 70.5
Cash and deferred incentive compensation [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Defined contribution plan, cost recognized		81.2	70.3	71.8
Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		273.0
Fair value of net assets available for plan benefits at end of year		103.9	273.0
Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		225.0
Fair value of net assets available for plan benefits at end of year		402.7	225.0
Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		5.9
Fair value of net assets available for plan benefits at end of year		$ 7.3	5.9
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Number of benefit plans | plan		1
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Projected benefit obligation at beginning of year		$ 452.8	604.6	639.7
Interest cost		23.4	16.4	15.2
Actuarial (gains) losses		10.9	(138.7)	(22.2)
Benefits paid		(30.7)	(29.5)	(28.0)
Net increase (decrease) for the year		3.6	(151.8)	(35.1)
Projected benefit obligation at end of year		456.4	452.8	604.6	$ 639.7
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		507.1	556.0	479.6
Actual return on plan assets		44.2	(19.2)	104.4
Benefits paid		(30.7)	(29.5)	(28.0)
Net increase (decrease) for year		13.4	(48.8)	76.3
Fair value of net assets available for plan benefits at end of year		520.6	507.1	556.0	$ 479.6
Defined Benefit Plan, Funded (Unfunded) Status of Plan		64.1	54.3	(48.6)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)		0.9	(18.3)	(9.8)
Net recognized loss		$ (27.8)	$ (38.5)	$ (123.2)
Settlement discount rates - Projected Benefit Obligation		5.15%	5.40%
Settlement discount rates - Net Periodic Benefit Costs		5.40%	2.80%	2.45%
Long-term rates of return on plans' assets		4.60%	7.00%	7.00%
Expected future benefit payments in year one		$ 33.7
Expected future benefit payments in year two		34.3
Expected future benefit payments in year three		34.9
Expected future benefit payments in year four		34.6
Expected future benefit payments in year five		34.6
Expected future benefit payments in five fiscal years thereafter		$ 169.4
Total investments		100.00%	100.00%
Pension Plans, Defined Benefit [Member] | Equity securities, other [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		$ 197.5
Fair value of net assets available for plan benefits at end of year			$ 197.5
Total investments		0.00%	38.90%
Pension Plans, Defined Benefit [Member] | Equity securities, other [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		$ 197.5
Fair value of net assets available for plan benefits at end of year			$ 197.5
Pension Plans, Defined Benefit [Member] | Equity securities, other [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		0.0
Fair value of net assets available for plan benefits at end of year			0.0
Pension Plans, Defined Benefit [Member] | Equity securities, other [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		0.0
Fair value of net assets available for plan benefits at end of year			0.0
Pension Plans, Defined Benefit [Member] | Equity Securities [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		$ 265.8
Fair value of net assets available for plan benefits at end of year			$ 265.8
Total investments		16.00%	52.40%
Pension Plans, Defined Benefit [Member] | Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		$ 265.8
Fair value of net assets available for plan benefits at end of year			$ 265.8
Pension Plans, Defined Benefit [Member] | Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		0.0
Fair value of net assets available for plan benefits at end of year			0.0
Pension Plans, Defined Benefit [Member] | Equity Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		0.0
Fair value of net assets available for plan benefits at end of year			0.0
Pension Plans, Defined Benefit [Member] | Fixed maturity securities [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		225.0
Fair value of net assets available for plan benefits at end of year		$ 406.5	$ 225.0
Total investments		78.10%	44.40%
Pension Plans, Defined Benefit [Member] | Fixed maturity securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		$ 0.0
Fair value of net assets available for plan benefits at end of year		3.7	$ 0.0
Pension Plans, Defined Benefit [Member] | Fixed maturity securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		225.0
Fair value of net assets available for plan benefits at end of year		402.7	225.0
Pension Plans, Defined Benefit [Member] | Fixed maturity securities [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		0.0
Fair value of net assets available for plan benefits at end of year		0.0	0.0
Pension Plans, Defined Benefit [Member] | Benefit plan assets, Other [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		13.0
Fair value of net assets available for plan benefits at end of year		$ 24.3	$ 13.0
Total investments		5.90%	3.20%
Pension Plans, Defined Benefit [Member] | Benefit plan assets, Other [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		$ 7.1
Fair value of net assets available for plan benefits at end of year		17.0	$ 7.1
Pension Plans, Defined Benefit [Member] | Benefit plan assets, Other [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		0.0
Fair value of net assets available for plan benefits at end of year		0.0	0.0
Pension Plans, Defined Benefit [Member] | Benefit plan assets, Other [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		5.9
Fair value of net assets available for plan benefits at end of year		7.3	5.9
Pension Plans, Defined Benefit [Member] | Defined Benefit Plan, Equity Securities, Common Stock, Employer, Related Party
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		68.3
Fair value of net assets available for plan benefits at end of year		$ 83.1	$ 68.3
Total investments		16.00%	13.50%
Pension Plans, Defined Benefit [Member] | Defined Benefit Plan, Equity Securities, Common Stock, Employer, Related Party | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		$ 68.3
Fair value of net assets available for plan benefits at end of year		83.1	$ 68.3
Pension Plans, Defined Benefit [Member] | Defined Benefit Plan, Equity Securities, Common Stock, Employer, Related Party | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		0.0
Fair value of net assets available for plan benefits at end of year		0.0	0.0
Pension Plans, Defined Benefit [Member] | Defined Benefit Plan, Equity Securities, Common Stock, Employer, Related Party | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		0.0
Fair value of net assets available for plan benefits at end of year		$ 0.0	$ 0.0
Minimum [Member] | Pension Plans, Defined Benefit [Member] | Equity Securities [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Current Investment Policy Asset Allocation % Range Target		0.00%
Minimum [Member] | Pension Plans, Defined Benefit [Member] | Fixed maturity securities [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Current Investment Policy Asset Allocation % Range Target		75.00%
Minimum [Member] | Pension Plans, Defined Benefit [Member] | Benefit plan assets, Other [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Current Investment Policy Asset Allocation % Range Target		1.00%
Maximum [Member] | Pension Plans, Defined Benefit [Member] | Equity Securities [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Current Investment Policy Asset Allocation % Range Target		25.00%
Maximum [Member] | Pension Plans, Defined Benefit [Member] | Fixed maturity securities [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Current Investment Policy Asset Allocation % Range Target		100.00%
Maximum [Member] | Pension Plans, Defined Benefit [Member] | Benefit plan assets, Other [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Current Investment Policy Asset Allocation % Range Target		10.00%
Common Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
stock acquired during period shares employee stock ownership plan | shares					3,337,000	2,383,625	2,200,000
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Restricted common stock vesting period		3 years
Range of Exercise Prices, $16.06[Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options, outstanding at end of year | shares		74,788
Exercisable at end of year | shares		74,788
Options, outstanding, weighted average exercise price | $ / shares		$ 16.06
Exercisable at end of year, Weighted Average Exercise Price | $ / shares		$ 16.06
Options, Outstanding, Weighted Average Remaining Contractual Life		3 months
Range of Exercise Prices, $15.26 [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options, outstanding at end of year | shares		123,061
Exercisable at end of year | shares		123,061
Options, outstanding, weighted average exercise price | $ / shares		$ 15.26
Exercisable at end of year, Weighted Average Exercise Price | $ / shares		$ 15.26
Options, Outstanding, Weighted Average Remaining Contractual Life		1 year 3 months
Range of Exercise Prices, $18.14 [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options, outstanding at end of year | shares		252,893
Exercisable at end of year | shares		252,893
Options, outstanding, weighted average exercise price | $ / shares		$ 18.14
Exercisable at end of year, Weighted Average Exercise Price | $ / shares		$ 18.14
Options, Outstanding, Weighted Average Remaining Contractual Life		2 years 3 months
Range of Exercise Prices, $19.98 [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options, outstanding at end of year | shares		407,633
Exercisable at end of year | shares		407,633
Options, outstanding, weighted average exercise price | $ / shares		$ 19.98
Exercisable at end of year, Weighted Average Exercise Price | $ / shares		$ 19.98
Options, Outstanding, Weighted Average Remaining Contractual Life		3 years 3 months
Range of Exercise Prices, $20.98 [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options, outstanding at end of year | shares		573,174
Exercisable at end of year | shares		573,174
Options, outstanding, weighted average exercise price | $ / shares		$ 20.98
Exercisable at end of year, Weighted Average Exercise Price | $ / shares		$ 20.98
Options, Outstanding, Weighted Average Remaining Contractual Life		4 years 3 months
Range of Exercise Prices, $21.12 to $21.99 [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options, outstanding at end of year | shares		973,628
Exercisable at end of year | shares		973,628
Options, outstanding, weighted average exercise price | $ / shares		$ 21.16
Exercisable at end of year, Weighted Average Exercise Price | $ / shares		$ 21.16
Options, Outstanding, Weighted Average Remaining Contractual Life		5 years 3 months
Range of Exercise Prices, $16.17 to $22.72 [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options, outstanding at end of year | shares		1,295,913
Exercisable at end of year | shares		878,634
Options, outstanding, weighted average exercise price | $ / shares		$ 17.45
Exercisable at end of year, Weighted Average Exercise Price | $ / shares		$ 17.50
Options, Outstanding, Weighted Average Remaining Contractual Life		6 years 3 months
Range of Exercise Prices, $21.30 [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options, outstanding at end of year | shares		1,761,193
Exercisable at end of year | shares		829,759
Options, outstanding, weighted average exercise price | $ / shares		$ 21.30
Exercisable at end of year, Weighted Average Exercise Price | $ / shares		$ 21.30
Options, Outstanding, Weighted Average Remaining Contractual Life		7 years 3 months
Range of Exercise Prices, $22.92 to $24.49 [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options, outstanding at end of year | shares		2,429,431
Exercisable at end of year | shares		677,001
Options, outstanding, weighted average exercise price | $ / shares		$ 23.30
Exercisable at end of year, Weighted Average Exercise Price | $ / shares		$ 23.33
Options, Outstanding, Weighted Average Remaining Contractual Life		8 years 3 months
Range of Exercise Prices, $24.31 to $25.52 [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options, outstanding at end of year | shares		2,978,500
Exercisable at end of year | shares		0
Options, outstanding, weighted average exercise price | $ / shares		$ 25.22
Exercisable at end of year, Weighted Average Exercise Price | $ / shares		$ 0
Options, Outstanding, Weighted Average Remaining Contractual Life		9 years 3 months

[1] Based on the Black-Scholes-Merton option pricing model and the assumptions outlined above.