Earnings Per Share (Summary of Computation of Basic and Diluted Earnings Per Share) (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Earnings Per Share [Abstract]
Net income attributable to common shareholders	$ 103	$ 42
Weighted-average common shares outstanding for basic earnings per share	169,595,951	165,703,279
Employee equity awards	4,070,605	3,958,437
Weighted-average common shares outstanding for diluted earnings per share	173,666,556	169,661,716
Basic earnings per share	$ 0.61	$ 0.26
Diluted earnings per share	$ 0.59	$ 0.25