Debt (Senior Notes) (Narrative) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified		12 Months Ended		0 Months Ended	12 Months Ended	0 Months Ended	12 Months Ended
	Apr. 24, 2009	Dec. 31, 2011 Senior Notes [Member]	Jul. 24, 2009 Senior Notes [Member]	Jul. 24, 2009 Senior Notes Due 2016 [Member]	Dec. 31, 2011 Senior Notes Due 2016 [Member]	Jul. 24, 2009 Senior Notes Due 2019 [Member]	Dec. 31, 2011 Senior Notes Due 2019 [Member]	Dec. 31, 2011 8.0% Senior Notes [Member]	Dec. 31, 2011 8.25% Senior Notes [Member]	Dec. 31, 2011 0.375% Convertible Senior Notes [Member]
Debt Instruments [Line Items]
Interest payable dates				February 15 and August 15		February 15 and August 15
Unsecured senior notes			$ 750.0	$ 375.0		$ 375.0
Debt instrument, maturity date				Aug. 15, 2016		Aug. 15, 2019
Interest rates for senior notes								8.00%	8.25%	0.375%
Deferred financing fees	7.7	16.5
Net proceeds of offering after deducting discounts		$ 727.8
Percentage of face value price for issuance of senior notes		35.00%		99.33%		99.152%
Temporary equity redemption percentage price					$ 108.00%		$ 108.25%