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Earnings Per Share
 12 Months Ended
Dec. 31, 2011
Earnings Per Share [Abstract]  
Earnings Per Share
EARNINGS PER SHARE

The calculation of earnings per share is as follows:
$ in millions, except per share data
Net Income Attributable to Common Shareholders
 
Weighted Average Number of Shares
 
Per Share Amount
For the year ended December 31, 2011
 
 
 
 
 
Basic earnings per share

$729.7

 
462.9

 

$1.58

Dilutive effect of share-based awards
—

 
1.8

 
—

Diluted earnings per share

$729.7

 
464.7

 

$1.57

For the year ended December 31, 2010
 
 
 
 
 
Basic earnings per share

$465.7

 
460.4

 

$1.01

Dilutive effect of share-based awards
—

 
2.8

 
—

Diluted earnings per share

$465.7

 
463.2

 

$1.01

For the year ended December 31, 2009
 
 
 
 
 
Basic earnings per share

$322.5

 
417.2

 

$0.77

Dilutive effect of share-based awards
—

 
6.4

 
—

Diluted earnings per share

$322.5

 
423.6

 

$0.76


See Note 12, “Share-Based Compensation,” for a summary of share awards outstanding under the company's share-based payment programs. These programs could result in the issuance of common shares that would affect the measurement of basic and diluted earnings per share.

Options to purchase 0.1 million common shares at a weighted average exercise price of £18.11 were outstanding during the year ended December 31, 2011 (December 31, 2010: 5.7 million share options at a weighted average exercise price of £19.47; December 31, 2009: 9.6 million share options at a weighted average exercise price of £20.30), but were not included in the computation of diluted earnings per share because the option's exercise price was greater than the average market price of the common shares and therefore their inclusion would have been anti-dilutive.

There were no time-vested share awards that were excluded from the computation of diluted earnings per share during the years ended December 31, 2011, 2010, and 2009 due to their inclusion being anti-dilutive. There were no contingently issuable shares excluded from the diluted earnings per share computation during year ended December 31, 2011 (December 31, 2010: none; December 31, 2009: 1.4 million contingently issuable shares), because the necessary performance conditions for the shares to be issuable had not yet been satisfied at the end of the respective period.