Equity and Capital Terms and Conditions of Preferred Stock (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Class of Stock [Line Items]
Preferred Stock, Shares Outstanding	11,000,000	11,000,000
Preferred Stock, Liquidation Preference Per Share	$ 275,000,000	$ 275,000,000
Distributions Paid To Preferred Unit Holders	7.45%
Distributions Paid To Preferred Unit Holders, Rate		7.45%
Series 3 [Member]
Class of Stock [Line Items]
Preferred Stock, Shares Outstanding	3,000,000	3,000,000
Preferred Stock, Liquidation Preference Per Share	$ 75,000,000	$ 75,000,000
Distributions Paid To Preferred Unit Holders	7.45%	7.45%
Series 4 [Member]
Class of Stock [Line Items]
Preferred Stock, Shares Outstanding	5,000,000	5,000,000
Preferred Stock, Liquidation Preference Per Share	$ 125,000,000	$ 125,000,000
Distributions Paid To Preferred Unit Holders	7.25%	7.25%
Series 5 [Member]
Class of Stock [Line Items]
Preferred Stock, Shares Outstanding	3,000,000	3,000,000
Preferred Stock, Liquidation Preference Per Share	$ 75,000,000	$ 75,000,000
Distributions Paid To Preferred Unit Holders	6.70%	6.70%