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		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings Per Share [Abstract]
Net income from continuing operations attributable to common stockholders	$ 584	$ 348	$ 959	$ 600
(Loss) income from discontinued operations, net of tax	(2)	1	(3)	(1)
Net income	$ 582	$ 349	$ 956	$ 599
Basic weighted-average common shares outstanding	398,100	430,628	401,098	433,405
Diluted weighted-average common shares outstanding	399,916	432,554	402,921	435,727
Earnings Per Share, Basic [Abstract]
Net income from continuing operations, basic earnings per common share	$ 1.47	$ 0.81	$ 2.39	$ 1.38
Loss from discontinued operations, net of tax, basic earnings per common share	0	0	(0.01)	0
Net income, basic earnings per common share	1.46	0.81	2.39	1.38
Earnings Per Share, Diluted [Abstract]
Net income from continuing operations, diluted earnings per common share	1.46	0.80	2.38	1.38
Loss from discontinued operations, net of tax, diluted earnings per common share	0	0	(0.01)	0
Net income, diluted earnings per common share	$ 1.46	$ 0.81	$ 2.37	$ 1.37