Borrowing Arrangements (Derivatives and Hedging (Details) - USD ($) $ in Millions	1 Months Ended			3 Months Ended
	Dec. 31, 2018	Aug. 31, 2018	Feb. 28, 2018	Mar. 31, 2017	Dec. 31, 2017	Feb. 28, 2017
Derivative [Line Items]
Derivative notional amount						$ 275.0
Derivative, Loss on Derivative	$ 5.1	$ 6.6
Derivative gain			$ 10.0	$ 0.8
Swaps terminated, notional amount	$ 200.0
4.00% Senior Notes due 2028
Derivative [Line Items]
Interest rate	4.00%		4.00%
3.85% Senior Notes due 2027
Derivative [Line Items]
Interest rate	3.85%			3.85%
3.25% Senior Notes due 2026
Derivative [Line Items]
Interest rate	3.25%
Senior Notes Due 2027
Derivative [Line Items]
Interest rate				3.85%
4.40% Senior Notes due 2029
Derivative [Line Items]
Interest rate	4.40%	4.40%
Derivative gain		$ 4.4
Swap | Variable Rate Debt
Derivative [Line Items]
Variable rate debt amount	$ 1,800.0
Derivative notional amount	148.8
Swap | Fixed Rate Debt
Derivative [Line Items]
Derivative notional amount	516.2
Fixed rate debt amount	9,000.0
Forward Contracts
Derivative [Line Items]
Derivative notional amount					$ 200.0
Weighted interest rate						2.33%
Interest Rate Swap
Derivative [Line Items]
Derivative notional amount				$ 400.0
Derivative, basis spread on variable rate				0.98%
Swap
Derivative [Line Items]
Derivative notional amount	$ 300.0	200.0
Swaps terminated, notional amount		$ 200.0