Summary of Significant Accounting Policies (Earnings Per Share) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Basic earnings per share – continuing operations:
Income from continuing operations, net of tax									$ 1,427	$ 879	$ 1,503
Participating securities dividends									(1)	0	0
Income from continuing operations available to common shareholders									1,426	879	1,503
Weighted average common shares outstanding (in shares)									326	326	326
Basic earnings (loss) per share – continuing operations (in dollars per share)	$ 1.17	$ 1.52	$ 1.08	$ 0.61	$ 0.81	$ 1.42	$ (0.33)	$ 0.79	$ 4.38	$ 2.70	$ 4.61
Diluted earnings per share – continuing operations:
Income from continuing operations available to common shareholders									1,426	879	1,503
Income impact of assumed conversions									1	1	(1)
Income from continuing operations available to common shareholders and assumed conversions									$ 1,427	$ 880	$ 1,502
Weighted average common shares outstanding (in shares)									326	326	326
Incremental shares from assumed conversions (in shares)									3	3	4
Adjusted weighted average shares - diluted (in shares)									329	329	330
Diluted earnings (loss) per share – continuing operations (in dollars per share)	$ 1.15	$ 1.51	$ 1.07	$ 0.61	$ 0.81	$ 1.41	$ (0.33)	$ 0.78	$ 4.33	$ 2.67	$ 4.55