Long-term Debt (Details) - USD ($) $ in Millions		6 Months Ended
		Jun. 30, 2015	Dec. 31, 2014
Statement of Financial Position [Abstract]
Long-term Debt		$ 1,624.8	$ 1,625.6
Less: current portion		2.0	2.1
Long-term Debt, Excluding Current Maturities		$ 1,622.8	1,623.5
2.25% Notes
Statement of Financial Position [Abstract]
Debt Instrument, Maturity Date		Nov. 15, 2017
Debt Instrument, Interest Rate, Stated Percentage		2.25%
Debt Instrument, Interest Rate, Effective Percentage		2.30%
Debt Instrument, Unamortized Discount		$ 0.3
Long-term Debt, Book Value		299.7	299.6
Long-term Debt, Fair Value	[1]	$ 303.2	301.2
4.00% Notes
Statement of Financial Position [Abstract]
Debt Instrument, Maturity Date		Mar. 15, 2022
Debt Instrument, Interest Rate, Stated Percentage		4.00%
Debt Instrument, Interest Rate, Effective Percentage		4.13%
Debt Instrument, Unamortized Discount		$ 2.1
Long-term Debt, Book Value		247.9	247.7
Long-term Debt, Fair Value	[1]	$ 255.2	255.2
3.75% Notes
Statement of Financial Position [Abstract]
Debt Instrument, Maturity Date		Feb. 15, 2023
Debt Instrument, Interest Rate, Stated Percentage		3.75%
Debt Instrument, Interest Rate, Effective Percentage		4.32%
Debt Instrument, Unamortized Discount		$ 1.2
Long-term Debt, Book Value		498.8	498.8
Long-term Debt, Fair Value	[1]	$ 495.8	499.8
4.20% Notes
Statement of Financial Position [Abstract]
Debt Instrument, Maturity Date		Apr. 15, 2024
Debt Instrument, Interest Rate, Stated Percentage		4.20%
Debt Instrument, Interest Rate, Effective Percentage		4.24%
Debt Instrument, Unamortized Discount		$ 0.8
Long-term Debt, Book Value		499.2	499.1
Long-term Debt, Fair Value	[1]	505.9	509.8
Other notes payable and capitalized leases
Statement of Financial Position [Abstract]
Long-term Debt, Book Value		79.2	80.4
Long-term Debt, Fair Value	[1]	$ 79.2	$ 80.4

[1] See Note 11 for information on the fair value measurement of our long-term debt.