Commitments and Contingent Liabilities Textuals (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019
Loss Contingencies [Line Items]
Rental expense for leased premises	$ 73.0	$ 69.0	$ 65.2
Operating Leases, Rent Expense	64.9
Operating Leases, Future Minimum Payments Due, Current	59.0	60.4
Operating Leases, Future Minimum Payments, Due in Two Years		48.9
Operating Leases, Future Minimum Payments, Due in Three Years		39.5
Operating Leases, Future Minimum Payments, Due in Four Years		32.7
Operating Leases, Future Minimum Payments, Due in Five Years		24.0
Operating Leases, Future Minimum Payments, Due Thereafter		103.6
Operating Lease, Liability	238.0
Retained earnings	$ 4,386.0	3,849.8
Operating Lease, Weighted Average Discount Rate, Percent	5.46%
Operating Lease, Weighted Average Remaining Lease Term	7 years 10 months 24 days
Lessee, Operating Lease, Liability, Payments, Due Year Two	$ 50.6
Lessee, Operating Lease, Liability, Payments, Due Year Three	42.9
Lessee, Operating Lease, Liability, Payments, Due Year Four	33.5
Lessee, Operating Lease, Liability, Payments, Due Year Five	24.4
Lessee, Operating Lease, Liability, Payments, Due after Year Five	100.9
Lessee, Operating Lease, Liability, Payments, Due	311.6
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	73.6
Operating Leases, Future Minimum Payments Due		$ 309.4
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