Debt and Credit Facilities (Narrative) (Details) (USD $)	12 Months Ended					1 Months Ended	6 Months Ended
	Dec. 31, 2010	Jun. 30, 2011	Feb. 15, 2011	Apr. 30, 2009	Dec. 31, 2001	Apr. 30, 2009 Exchangeable Senior Notes [Member]	Jun. 30, 2011 Debentures With Put Feature [Member]	Jun. 30, 2011 Four Year Revolving Credit Facility [Member]	May 31, 2013 Three Year Revolving Credit Facility [Member]	Jun. 30, 2011 Three Year Revolving Credit Facility [Member]
Long-term debenture with fixed interest rate		$ 343,600,000
Debt instrument, maturity date range, start							2027
Debt instrument, maturity date range, end							2028
Debentures with put option exercised	100,000
Debentures with put option available to be exercised			37,200,000
Senior note issued						345,000,000
Stated interest rate for debt instruments					11.00%	4.50%
Portion of convertible debt allocated to debt				305,000,000
Portion of convertible debt allocated to equity, gross				40,000,000
Portion of convertible debt allocated to equity, net of allocated fees				39,000,000
Fair value of debt	4,131,800,000	4,097,100,000
Line of credit facility, amount outstanding		2,000,000,000						1,000,000,000	1,000,000,000
Line of credit facilities, amounts expired										$ 1,000,000,000