Summary of Significant Accounting Policies (Earnings Per Share) (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Basic earnings per share - continuing operations:
Income from continuing operations attributable to common shareholders, net of tax									$ 1,503	$ 1,041	$ 1,092
Participating securities dividends									0	0	(5)
Income from continuing operations available to common shareholders									1,503	1,041	1,087
Weighted average common shares outstanding (in shares)									326,000,000	326,000,000	326,000,000
Basic earnings (loss) per share – continuing operations (in dollars per share)	$ 2.42	$ 1.09	$ 0.57	$ 0.54	$ 0.68	$ 1.21	$ 0.64	$ 0.67	$ 4.61	$ 3.20	$ 3.34
Diluted earnings per share - continuing operations:
Income from continuing operations available to common shareholders									1,503	1,041	1,087
Income impact of assumed conversions									(1)	(1)	5
Income from continuing operations available to common shareholders and assumed conversions									$ 1,502	$ 1,040	$ 1,092
Weighted average common shares outstanding (in shares)									326,000,000	326,000,000	326,000,000
Incremental shares from assumed conversions (in shares)									4,000,000	3,000,000	3,000,000
Adjusted weighted average shares - diluted (in shares)									330,000,000	329,000,000	329,000,000
Diluted earnings (loss) per share – continuing operations (in dollars per share)	$ 2.39	$ 1.09	$ 0.55	$ 0.54	$ 0.66	$ 1.20	$ 0.64	$ 0.67	$ 4.55	$ 3.17	$ 3.32
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)					5,847,094				7,492,552		5,981,090