Debt (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Debt Instrument [Line Items]
Weighted average interest rate	0.30%
Long-term Debt	$ 1,315.9	$ 1,421.6
Commercial paper, maximum amount outstanding during period	491.0
Commercial paper, average outstanding amount	323.9
Line of credit, maximum borrowing capacity	1,100
Line of Credit Facility, Maximum Borrowing Capacity, Multicurrency Limit	100
Derivative Instruments, Gain (Loss) Recognized in Income, Net	7.8	8.2	7.8
Current portion of long-term debt	0	0.2
Long-term Debt and Capital Lease Obligations	1,315.9	1,421.4
Long-term Debt, Fiscal Year Maturity [Abstract]
2015	317.3
2016	0
2017	0
2018	0
2019	399.4
Commercial Paper [Member]
Debt Instrument [Line Items]
Weighted average interest rate	0.50%
Long-term Debt	317.3	240.5
Notes Payable 5.65 Percent Due 2014 [Member]
Debt Instrument [Line Items]
Weighted average interest rate	5.65%
Long-term Debt	0	399.9
Debt instrument, face amount	400.0
Unamortized discount	0	0.1
Notes Payable 6.8 Percent Due 2019 [Member]
Debt Instrument [Line Items]
Weighted average interest rate	6.80%
Long-term Debt	399.4	399.3
Unamortized discount	0.6	0.7
Notes Payable 4.5 Percent Due 2021 [Member]
Debt Instrument [Line Items]
Weighted average interest rate	4.50%
Long-term Debt	399.2	377.8
Debt instrument, face amount	400.0
Fixed-rate (as a percent)	4.50%
Unamortized discount	1.8	2.0
Note Payable LIBOR plus fixed spread due 2022 [Member]
Debt Instrument [Line Items]
Long-term Debt	200.0	0
Debt instrument, face amount	200.0
Debt of Subsidiary Companies Due 2013 [Member]
Debt Instrument [Line Items]
Long-term Debt	0	3.9
Capital Lease Obligations [Member]
Debt Instrument [Line Items]
Long-term Debt	0	0.2
Interest-rate swap | Measured on a recurring basis | (Level 2)
Debt Instrument [Line Items]
Derivative Asset	1.0	0
Derivative Liability	0	(20.2)
Derivatives designated as hedging instruments | Interest-rate swap
Debt Instrument [Line Items]
Number of swap agreements	4
Notional amounts of derivatives	400.0
Derivative Instruments, Gain (Loss) Recognized in Income, Net	$ 8.2	$ 8.1	$ 7.0