Indebtedness - Overview (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Debt Disclosure [Abstract]
Debt, Weighted Average Interest Rate	5.00%us-gaap_DebtWeightedAverageInterestRate	5.10%us-gaap_DebtWeightedAverageInterestRate	5.30%us-gaap_DebtWeightedAverageInterestRate
Interest Costs, Capitalized During Period	$ 13.2us-gaap_InterestCostsCapitalized	$ 9.6us-gaap_InterestCostsCapitalized	$ 9.9us-gaap_InterestCostsCapitalized
Cash paid for interest	$ 164.9us-gaap_InterestPaid	$ 143.2us-gaap_InterestPaid	$ 132.2us-gaap_InterestPaid

The amount of cash paid for interest during the period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4297-108586

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 25

-Subparagraph (e)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3536-108585

Name:	us-gaap_InterestPaid
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration