Summary of Significant Accounting Policies (Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Basic earnings per share – continuing operations:
Income from continuing operations attributable to common shareholders	$ 513	$ 470	$ 1,007	$ 1,110
Participating securities dividends	0	0	0	0
Income from continuing operations available to common shareholders	$ 513	$ 470	$ 1,007	$ 1,110
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)	$ 1.57	$ 1.44	$ 3.09	$ 3.41
Diluted earnings per share – continuing operations:
Income from continuing operations attributable to common shareholders	$ 513	$ 470	$ 1,007	$ 1,110
Participating securities dividends	0	0	0	0
Income from continuing operations available to common shareholders	513	470	1,007	1,110
Income impact of assumed conversions	0	0	0	0
Income from continuing operations available to common shareholders and assumed conversions	$ 513	$ 470	$ 1,007	$ 1,110
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)	1,000,000	2,000,000	1,000,000	3,000,000
Adjusted weighted average shares - diluted (in shares)	327,000,000	328,000,000	327,000,000	329,000,000
Diluted earnings per share - continuing operations (in dollars per share)	$ 1.57	$ 1.43	$ 3.08	$ 3.38
Stock option awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Stock-based compensation awards excluded from the computation of diluted earnings per share (in shares)	3,817,072	1,365,671	6,042,695	1,373,736