Annual report pursuant to Section 13 and 15(d)

Unsecured Lines Of Credit Payable (Lines Of Credit Unused And Available) (Details)

v2.4.0.6
Unsecured Lines Of Credit Payable (Lines Of Credit Unused And Available) (Details) (USD $)
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Line of Credit Facility [Line Items]      
Committed capacity $ 475,000,000 $ 337,000,000 $ 337,000,000
Borrowings outstanding (99,000,000) (100,000,000) (128,000,000)
Credit Facility No. 1 [Member]
     
Line of Credit Facility [Line Items]      
Committed capacity 75,000,000    
Borrowings outstanding 74,000,000 0  
Letters of credit issued 800,000    
Unused and available 200,000    
Credit Facility No. 2 [Member]
     
Line of Credit Facility [Line Items]      
Committed capacity 400,000,000    
Borrowings outstanding 25,000,000 (100,000,000)  
Letters of credit issued 0    
Unused and available $ 375,000,000