Debt (Senior Notes) (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2014
2023 Senior notes [Member]
Debt Instrument [Line Items]
Debt instrument, issuance date	Nov. 01, 2013
Debt instrument, face amount	$ 300.0
Debt instrument, maturity date	Nov. 15, 2023
2022 Senior notes [Member]
Debt Instrument [Line Items]
Debt instrument, issuance date	Sep. 11, 2012
Debt instrument, face amount	$ 500.0
Debt instrument, maturity date	Sep. 15, 2022