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		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share [Abstract]
Net income from continuing operations attributable to common stockholders	$ 381	$ 374	$ 1,340	$ 974
Loss from discontinued operations, net of tax	0	0	(3)	(1)
Net income	$ 381	$ 374	$ 1,337	$ 973
Basic weighted-average common shares outstanding	390,205	422,187	397,427	429,625
Diluted weighted-average common shares outstanding	392,604	424,784	399,442	432,038
Earnings Per Share, Basic [Abstract]
Net income from continuing operations, basic earnings per common share	$ 0.98	$ 0.89	$ 3.37	$ 2.27
Loss from discontinued operations, net of tax, basic earnings per common share	0	0	(0.01)	0
Net income, basic earnings per common share	0.97	0.89	3.36	2.26
Earnings Per Share, Diluted [Abstract]
Net income from continuing operations, diluted earnings per common share	0.97	0.88	3.35	2.25
Loss from discontinued operations, net of tax, diluted earnings per common share	0	0	(0.01)	0
Net income, diluted earnings per common share	$ 0.97	$ 0.88	$ 3.35	$ 2.25