Summary of Significant Accounting Policies (Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Basic earnings per share – continuing operations:
Income from continuing operations attributable to common shareholders	$ 392	$ 276	$ 670	$ 494
Participating securities dividends	0	0	0	0
Income from continuing operations available to common shareholders	$ 392	$ 276	$ 670	$ 494
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)	$ 1.20	$ 0.85	$ 2.05	$ 1.52
Diluted earnings per share – continuing operations:
Income from continuing operations attributable to common shareholders	$ 392	$ 276	$ 670	$ 494
Participating securities dividends	0	0	0	0
Income from continuing operations available to common shareholders	392	276	670	494
Income impact of assumed conversions	0	0	0	0
Income from continuing operations available to common shareholders and assumed conversions	$ 392	$ 276	$ 670	$ 494
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	1,000,000	1,000,000	1,000,000
Adjusted weighted average shares - diluted (in shares)	327,000,000	327,000,000	327,000,000	327,000,000
Diluted earnings per share - continuing operations (in dollars per share)	$ 1.20	$ 0.84	$ 2.05	$ 1.51
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)	7,426,319	6,223,964	7,435,580	6,223,964