Debt (Narratives) (Details) $ / shares in Units, € in Millions, $ in Millions	1 Months Ended		3 Months Ended																7 Months Ended	12 Months Ended
	Sep. 30, 2015 CLF	Sep. 30, 2015 USD ($) $ / shares	Sep. 30, 2016 USD ($)	[1]	Jun. 30, 2016 USD ($)	[1]	Mar. 31, 2016 USD ($)	[1]	Dec. 31, 2015 USD ($)	[1]	Sep. 30, 2015 USD ($)		Jun. 30, 2015 USD ($)	[1]	Mar. 31, 2015 USD ($)	[1]	Dec. 31, 2014 USD ($)	[1]	Apr. 30, 2013	Sep. 30, 2016 USD ($)		Sep. 30, 2015 USD ($)		Sep. 30, 2014 USD ($)	Sep. 30, 2016 EUR (€)	Sep. 30, 2016 USD ($)
Debt Instruments [Abstract]
Short-term debt, weighted average interest rate		0.80%									0.80%											0.80%			1.10%	1.10%
Cash paid for interest, net of amounts capitalized																				$ 121.1		$ 97.5		$ 132.4
Debt Instrument [Line Items]
Payments on long-term debt																				485.0		708.7		608.6
Loss on extinguishment of debt			$ 6.9		$ 0.0		$ 0.0		$ 0.0		$ 16.6	[1]	$ 0.0		$ 0.0		$ 0.0			$ 6.9	[1]	16.6	[1]	$ 0.0
Eurobonds .375%
Debt Instrument [Line Items]
Debt instrument, issuance date																				Jun. 01, 2016
Debt instrument, maturity date																				Jun. 01, 2021
Debt Payable In Other Currencies		$ 0.0									0.0											0.0				$ 393.2
Interest rate of debt, stated percentage																									0.375%	0.375%
Debt instrument, maturity year																				2021
Debt instrument, principal amount																									€ 350	$ 386.9
Note 2.0%
Debt Instrument [Line Items]
Debt instrument, maturity date																				Aug. 02, 2016
Senior Notes		$ 350.0									$ 350.0											$ 350.0				$ 0.0
Interest rate of debt, stated percentage																									2.00%	2.00%
Debt instrument, maturity year																				2016
Payments on long-term debt																				$ 350.0
CLP Series E bonds 6.3%
Debt Instrument [Line Items]
Debt instrument, maturity date	Jan. 22, 2030	Jan. 22, 2030
Payments on long-term debt		$ 146.6
Loss on extinguishment of debt		16.6
Loss on extinguishment of debt, net of tax		$ 14.2
Loss on extinguishment of debt, per share, net of tax | $ / shares		$ 0.07
Extinguishment of debt amount	CLF 3,000,000	$ 130.0
Revolving Credit Facility [Member] | Credit Agreement 2013 Member [Member]
Debt Instrument [Line Items]
Credit facility, initiation date																				Apr. 30, 2013
Credit facility, length credit agreement in years																			5 years
Credit facility, maximum borrowing capacity																										$ 2,690.0
Credit facility, expiration date																				Apr. 30, 2018
Credit facility, amount borrowed and outstanding																										$ 0.0
Revolving Credit Facility [Member] | Credit Agreement 2013 Member [Member] | Maximum [Member]
Debt Instrument [Line Items]
Covenant, ratio of total debt to total capitalization																									70.00%	70.00%
Foreign Subsidiary Facility [Member]
Debt Instrument [Line Items]
Credit facility, maximum borrowing capacity																										$ 51.3
Credit facility, amount borrowed and outstanding																										$ 51.3

[1] For additional information, see Note 15, Debt.