Summary of Significant Accounting Policies (Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Basic earnings per share – continuing operations:
Income from continuing operations attributable to common shareholders	$ 278	$ 218
Participating securities dividends	0	0
Income from continuing operations available to common shareholders	$ 278	$ 218
Weighted average common shares outstanding (in shares)	326,000,000	326,000,000
Basic earnings per share - continuing operations (in dollars per share)	$ 0.85	$ 0.67
Diluted earnings per share – continuing operations:
Income from continuing operations attributable to common shareholders	$ 278	$ 218
Participating securities dividends	0	0
Income from continuing operations available to common shareholders	278	218
Income impact of assumed conversions	0	0
Income from continuing operations available to common shareholders and assumed conversions	$ 278	$ 218
Weighted average common shares outstanding (in shares)	326,000,000	326,000,000
Incremental shares from assumed conversions (in shares)	1,000,000	1,000,000
Adjusted weighted average shares - diluted (in shares)	327,000,000	327,000,000
Diluted earnings per share - continuing operations (in dollars per share)	$ 0.85	$ 0.67
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)	7,719,306	6,222,294