Significant Financing Transactions - (Narrative) (Details) (USD $)	3 Months Ended			1 Months Ended
	Mar. 31, 2012 Convertible Debt [Member]	Mar. 31, 2012 Convertible Debt [Member] Minimum	Mar. 31, 2012 Convertible Debt [Member] Maximum	Feb. 28, 2012 September 2006 hybrids [Member]	Mar. 31, 2012 September 2006 hybrids [Member]
Contingent convertible senior notes	$ 137,000,000
Conversion rate, shares of common stock per $1,000 principal amount of senior notes (in shares)	29.0360
Principal amount of senior notes	1,000
Conversion rate, shares of common stock per $1,000 principal amount of senior notes, conversion price	$ 34.44
Average Trading Price Principal Amount Of Senior Notes	120.00%
Minimum consecutive trading days		20 days
Maximum consecutive trading days			30 days
Debt Conversion, Converted Instrument, Amount	6,000,000
Tender Offer To Purchase Hybrid Subordinated Notes				150,000,000
Purchased And Cancelled Of Junior Subordinated Notes					$ 86,000,000