Commitments and Contingencies Operating Lease Liabilities (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Operating Lease Maturities [Abstract]
Lessee, Operating Lease, Liability, Payments, Due Next Rolling Twelve Months	$ 20.0
Lessee, Operating Lease, Liability, Payments, Due in Rolling Year Two	16.0
Lessee, Operating Lease, Liability, Payments, Due in Rolling Year Three	12.0
Lessee, Operating Lease, Liability, Payments, Due in Rolling Year Four	12.0
Lessee, Operating Lease, Liability, Payments, Due in Rolling Year Five	11.0
Lessee, Operating Lease, Liability, Payments, Due after Year Five	35.0
Lessee, Operating Lease, Liability, Payments, Due	106.0	$ 0.0
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	(12.0)
Operating Lease, Liability	94.0
Operating and Variable Lease Expense	6.0
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ 11.0
Operating Lease, Weighted Average Remaining Lease Term	7 years
Operating Lease, Weighted Average Discount Rate, Percent	3.30%
Operating Leases, Future Minimum Payments Due, Next Twelve Months		19.0
Operating Leases, Future Minimum Payments, Due in Two Years		14.0
Operating Leases, Future Minimum Payments, Due in Three Years		11.0
Operating Leases, Future Minimum Payments, Due in Four Years		10.0
Operating Leases, Future Minimum Payments, Due in Five Years		9.0
Operating Leases, Future Minimum Payments, Due Thereafter		34.0
Operating Leases, Future Minimum Payments Due		$ 97.0