Quarterly report pursuant to Section 13 or 15(d)

Capital Stock (Details)

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Capital Stock (Details) (USD $)
In Millions, except Share data, unless otherwise specified
 3 Months Ended 9 Months Ended
Sep. 30, 2011
Jun. 30, 2011
Mar. 31, 2011
Sep. 30, 2011
Aug. 15, 2011
Jun. 13, 2011
May 17, 2011
Dec. 31, 2010
Jun. 30, 2010
Jun. 13, 2011
Common Stock [Member]
Jun. 13, 2011
Over-allotment Option [Member]
May 25, 2011
Preferred Class A [Member]
May 25, 2011
Preferred Class B [Member]
May 17, 2011
Maximum [Member]
Shares authorized to be repurchased         4,000,000                  
Stock repurchased during period, shares 3,000,000                          
Stock repurchased during period, value $ 222                          
Treasury stock acquired, cost per share $ 74                          
Remaining number of shares authorized to be repurchased 1,000,000     1,000,000                    
Common shares, issued 149,195,469     149,195,469   10,350,000   138,845,469   9,000,000 1,350,000      
Price per share $ 85.63     $ 85.63                    
Proceeds from issuance of common stock $ 853.7     $ 853.7                    
Percentage increase in dividends payable       100.00%                    
Dividend payable, per share $ 0.28     $ 0.28       $ 0.0875 $ 0.14          
Common share dividends date paid Jun. 01, 2011 Mar. 01, 2011
Common share dividends date of record Apr. 29, 2011 Feb. 15, 2011
Common shares, authorized 400,000,000     400,000,000     224,000,000 224,000,000           400,000,000
Total shares, authorized             231,000,000             407,000,000
Preferred stock, shares included in amendment                       3,000,000 4,000,000