Earnings per Common Share (Schedule of Basic and Diluted Earnings per Common Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Earnings Per Share [Abstract]
Net income from continuing operations attributable to common shareholders	$ 375	$ 252
Income (loss) from discontinued operations, net of tax	(1)	(2)
Net income attributable to common stockholders	$ 374	$ 250
Basic weighted-average common shares outstanding	404,129	436,213
Diluted weighted-average common shares outstanding	405,959	438,931
Earnings Per Share, Basic [Abstract]
Net income from continuing operations, basic earnings per common share	$ 0.93	$ 0.58
Income (loss) from discontinued operations, net of tax, basic earnings per common share	0.00	(0.01)
Net income, basic earnings per common share	0.93	0.57
Earnings Per Share, Diluted [Abstract]
Net income from continuing operations, diluted earnings per common share	0.92	0.57
Income (loss) from discontinued operations, net of tax, diluted earnings per common share	0.00	(0.01)
Net income, diluted earnings per common share	$ 0.92	$ 0.57