Asset Retirement Obligations (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Future cash flows to settle asset retirement obligations	$ 352.5	$ 275.0
Minimum [Member]
Number of years to settle retirement obligations	1 year
Maximum [Member]
Number of years to settle retirement obligations	45 years