Commitments and Contingencies Operating Lease Liabilities (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Operating Lease Maturities [Abstract]
Lessee, Operating Lease, Liability, Payments, Due Next Rolling Twelve Months	$ 20.0	$ 20.0
Lessee, Operating Lease, Liability, Payments, Due in Rolling Year Two	16.0	16.0
Lessee, Operating Lease, Liability, Payments, Due in Rolling Year Three	13.0	13.0
Lessee, Operating Lease, Liability, Payments, Due in Rolling Year Four	13.0	13.0
Lessee, Operating Lease, Liability, Payments, Due in Rolling Year Five	13.0	13.0
Lessee, Operating Lease, Liability, Payments, Due after Year Five	32.0	32.0
Lessee, Operating Lease, Liability, Payments, Due	107.0	107.0
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	(12.0)	(12.0)
Operating Lease, Liability	95.0	95.0	$ 0.0
Operating and Variable Lease Expense	5.0	11.0
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ 6.0	$ 17.0
Operating Lease, Weighted Average Remaining Lease Term	7 years	7 years
Operating Lease, Weighted Average Discount Rate, Percent	3.40%	3.40%
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