Summary of Significant Accounting Policies (Earnings Per Share) (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Basic earnings per share - continuing operations:
Income from continuing operations attributable to common shareholders, net of tax	$ 266	$ 411	$ 486	$ 805
Participating securities dividends	0	0	0	0
Income from continuing operations available to common shareholders	266	411	486	805
Weighted average common shares outstanding (in shares)	326,000,000	326,000,000	326,000,000	326,000,000
Basic earnings per share - continuing operations (in dollars per share)	$ 0.81	$ 1.26	$ 1.49	$ 2.47
Diluted earnings per share - continuing operations:
Income from continuing operations available to common shareholders	266	411	486	805
Income impact of assumed conversions	0	2	1	3
Income from continuing operations available to common shareholders and assumed conversions	$ 266	$ 413	$ 487	$ 808
Weighted average common shares outstanding (in shares)	326,000,000	326,000,000	326,000,000	326,000,000
Incremental shares from assumed conversions (in shares)	3,000,000	3,000,000	2,000,000	3,000,000
Adjusted weighted average shares - diluted (in shares)	329,000,000	329,000,000	328,000,000	329,000,000
Diluted earnings per share - continuing operations (in dollars per share)	$ 0.81	$ 1.25	$ 1.48	$ 2.46
Stock-Based Compensation Awards
Antidilutive Securities Excluded from Computation of Earnings Per Share
Stock-based compensation awards excluded from the computation of diluted earnings per share (in shares)	3,238,581	5,943,378	4,819,683	8,970,290