Summary of Significant Accounting Policies (Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Basic earnings per share – continuing operations:
Income from continuing operations attributable to common shareholders	$ 378	$ 496	$ 1,056	$ 1,046
Participating securities dividends	0	0	(1)	0
Income from continuing operations available to common shareholders	$ 378	$ 496	$ 1,055	$ 1,046
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)	$ 1.16	$ 1.52	$ 3.24	$ 3.21
Diluted earnings per share – continuing operations:
Income from continuing operations available to common shareholders	$ 378	$ 496	$ 1,055	$ 1,046
Income impact of assumed conversions	0	0	1	1
Income from continuing operations available to common shareholders and assumed conversions	$ 378	$ 496	$ 1,056	$ 1,047
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)	2,000,000	3,000,000	3,000,000	3,000,000
Adjusted weighted average shares - diluted (in shares)	328,000,000	329,000,000	329,000,000	329,000,000
Diluted earnings per share – continuing operations (in dollars per share)	$ 1.15	$ 1.51	$ 3.21	$ 3.18
Stock-Based Compensation Awards
Diluted earnings per share – continuing operations:
Stock-based compensation awards excluded from the computation of diluted earnings per share (in shares)	2,054,876	38,800	2,054,876	62,885