Debt (Narratives) (Details) $ / shares in Units, € in Millions, $ in Millions	1 Months Ended		3 Months Ended								5 Months Ended		7 Months Ended	12 Months Ended
	Sep. 30, 2015 CLF	Sep. 30, 2015 USD ($) $ / shares	Sep. 30, 2015 USD ($)	[1]	Jun. 30, 2015 USD ($)	[1]	Mar. 31, 2015 USD ($)	[1]	Dec. 31, 2014 USD ($)	[1]	Mar. 10, 2015 EUR (€)	Mar. 10, 2015 USD ($)	Apr. 30, 2013	Sep. 30, 2015 USD ($)		Sep. 30, 2014 USD ($)	Sep. 30, 2013 USD ($)	Sep. 30, 2015 EUR (€)	Sep. 30, 2015 USD ($)
Debt Instruments [Abstract]
Short-term debt, weighted average interest rate																1.50%		0.80%	0.80%
Cash paid for interest, net of amounts capitalized														$ 97.5		$ 132.4	$ 136.1
Debt Instrument [Line Items]
Payments on long-term debt														708.7		608.6	437.5
Loss on early retirement of debt			$ 16.6		$ 0.0		$ 0.0		$ 0.0					$ 16.6	[1]	0.0	$ 0.0
CLP Series E bonds 6.3%
Debt Instrument [Line Items]
Debt instrument, maturity date	Jan. 22, 2030	Jan. 22, 2030
Debt Payable In Other Currencies																143.1			$ 0.0
Interest rate of debt, stated percentage																		6.30%	6.30%
Debt instrument, maturity year														2030
Payments on long-term debt		$ 146.6
Loss on early retirement of debt		16.6
Loss on early retirement of debt, net of tax		$ 14.2
Loss on early retirement of debt, per share, net of tax | $ / shares		$ 0.07
Extinguishment of debt amount	CLF 3,000,000	$ 130.0
Eurobond 3.875%
Debt Instrument [Line Items]
Debt instrument, maturity date											Mar. 10, 2015	Mar. 10, 2015
Interest rate of debt, stated percentage											3.875%	3.875%
Payments on long-term debt											€ 300	$ 335.9
Eurobonds 1.0%
Debt Instrument [Line Items]
Debt instrument, issuance date														Feb. 12, 2015
Debt instrument, maturity date														Feb. 12, 2025
Debt Payable In Other Currencies																$ 0.0			$ 335.2
Interest rate of debt, stated percentage																		1.00%	1.00%
Debt instrument, maturity year														2025
Debt instrument, principal amount																		€ 300	$ 335.3
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																			$ 119.4
Credit facility, amount borrowed and outstanding																			$ 110.6

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