Commitments and Contingent Liabilities Textuals (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jan. 01, 2019
Loss Contingencies [Line Items]
Rental expense for leased premises	$ 73.9	$ 73.0	$ 69.0
Operating Leases, Rent Expense	64.0	64.9
Operating Leases, Future Minimum Payments Due, Current	61.3	59.0
Operating Leases, Future Minimum Payments, Due in Two Years	54.0	50.6
Operating Leases, Future Minimum Payments, Due in Three Years	43.7	42.9
Operating Leases, Future Minimum Payments, Due in Four Years	34.0	33.5
Operating Leases, Future Minimum Payments, Due in Five Years	27.1	24.4
Operating Leases, Future Minimum Payments, Due Thereafter	96.4	100.9
Operating Lease, Liability	$ 247.6	238.0
Operating Lease, Weighted Average Discount Rate, Percent	5.37%
Operating Lease, Weighted Average Remaining Lease Term	7 years 7 months 6 days
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	$ 69.3	73.6
Operating Leases, Future Minimum Payments Due	316.8	311.6
Retained earnings	4,394.8	$ 4,386.0
Affiliated Entity [Member] | Financial Guarantee [Member]
Loss Contingencies [Line Items]
Guarantor Obligations, Current Carrying Value	$ 12.5
Accounting Standards Update 2016-02 [Member]
Loss Contingencies [Line Items]
Operating Lease, Right-of-Use Asset				$ 226.9
Operating Lease, Liability				241.4
Retained earnings				$ 18.4