Summary of Significant Accounting Policies (Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Basic earnings per share:
Income from operations attributable to common shareholders	$ 471	$ 513	$ 1,141	$ 1,007
Participating securities dividends	0	0	0	0
Net income available to common shareholders	$ 471	$ 513	$ 1,141	$ 1,007
Weighted average common shares outstanding (in shares)	347,000,000	326,000,000	333,000,000	326,000,000
Basic earnings per share - continuing operations (in dollars per share)	$ 1.36	$ 1.57	$ 3.43	$ 3.09
Diluted earnings per share:
Income from operations attributable to common shareholders	$ 471	$ 513	$ 1,141	$ 1,007
Participating securities dividends	0	0	0	0
Net income available to common shareholders	471	513	1,141	1,007
Income impact of assumed conversions	0	0	0	0
Net income available to common shareholders and assumed conversions	$ 471	$ 513	$ 1,141	$ 1,007
Weighted average common shares outstanding (in shares)	347,000,000	326,000,000	333,000,000	326,000,000
Incremental shares from assumed conversions (in shares)	2,000,000	1,000,000	1,000,000	1,000,000
Adjusted weighted average shares - diluted (in shares)	349,000,000	327,000,000	334,000,000	327,000,000
Diluted earnings per share - continuing operations (in dollars per share)	$ 1.35	$ 1.57	$ 3.42	$ 3.08
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)	1,398,884	3,817,072	5,997,917	6,042,695