Debt (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended			9 Months Ended
	Aug. 31, 2016	Sep. 30, 2016	Sep. 30, 2015	Jun. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Aug. 01, 2016	Mar. 31, 2015	Mar. 31, 2013	Jun. 30, 2009	Mar. 31, 2008	Jun. 30, 2003
Debt Instrument [Line Items]
Amount outstanding under revolving credit facility		$ 0.0			$ 0.0
Standby letters of credit, recorded liability		34.0			34.0
Revolving credit facility draw down amount without violating covenant		366.0			366.0
Gain (Loss) on Extinguishment of Debt		3.9	$ (5.5)		$ 3.9	$ (5.5)
Loss on extinguishment, amortization of deferred hedge gain		12.8
Debt repurchase, premium paid		5.8
Deferred loss - treasury lock agreements		1.2
Write off of Deferred Debt Issuance Cost				$ 2.5
Credit ratings					Our long-term credit ratings are: Moody’s ratings of Negative Outlook with Ba3 for corporate family debt, B1 for senior unsecured debt, and Ba1 for the Senior Secured Notes; S&P ratings of Stable Outlook with B for corporate family debt and BB- for the Senior Secured Notes; and Fitch rating of Negative Outlook with B+, each of which are below investment grade.
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility		400.0			$ 400.0
Debt Instrument, Interest Rate Terms			Borrowings under the 2015 facility bear interest, at our option, at a rate per annum equal to LIBOR plus 250 basis points or a floating base rate plus 150 basis points, in each case subject to adjustment based upon a leverage-based pricing grid.
2013 Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate Terms					The indenture governing the 2013 Notes contains interest rate adjustment provisions depending on the long-term credit ratings assigned to the 2013 Notes with S&P and Moody's. As described in the indenture, the interest rates on the 2013 Notes increase by .25% for each one-notch downgrade below investment grade on each of our long-term credit ratings assigned to the 2013 Notes by S&P or Moody's. These adjustments are limited to a total increase of 2% above the respective interest rates in effect on the date of issuance of the 2013 Notes.
2013 Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility								$ 1,000.0
Six Point Five Percent Notes Due March Two Thousand Nineteen [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage										6.50%
Repayments of Other Long-term Debt	$ 68.1
Five Point Seven Five Percent Notes, Due March Two Thousand Eighteen [Member]
Debt Instrument [Line Items]
Cash tender offer, deal costs [Line Items]		1.0
Debt Instrument, Interest Rate, Stated Percentage											5.75%
Repayments of Other Long-term Debt	108.6
Write off of Deferred Debt Issuance Cost		$ 0.9
Four Point Two Percent Notes, Due July Two Thousand Eighteen [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage												4.20%
Repayments of Other Long-term Debt	73.8
Two Point Three Seven Five Percent Notes, Due March Two Thousand Sixteen [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount									$ 250.0
Gain (Loss) on Extinguishment of Debt			$ 5.5
Notes Make Whole Premium			5.0			$ 5.0
Debt Instrument, Interest Rate, Stated Percentage									2.375%
Write off of Deferred Debt Issuance Cost			$ 0.5
Prepayment percent			100.00%
Accrued Interest Paid on Extinguishment of 2.375% Notes			$ 3.1
Four Point Six Zero Percent Notes, Due March Two Thousand Twenty [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount									$ 500.0
Debt Instrument, Interest Rate, Stated Percentage									4.60%
Repayments of Other Long-term Debt	$ 50.1
Five Point Zero Percent Notes, Due March Two Thousand Twenty-Three [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount									$ 500.0
Debt Instrument, Interest Rate, Stated Percentage									5.00%
Six Point Nine Five Percent Notes, Due March Two Thousand Forty-Three [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount									$ 250.0
Debt Instrument, Interest Rate, Stated Percentage									6.95%
Seven Point Eight Seven Five Percent Notes, Due August Two Thousand Twenty Two [Domain]
Debt Instrument [Line Items]
Debt Instrument, Face Amount							$ 500.0
Debt Instrument, Interest Rate, Stated Percentage							7.875%