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, 2018	Mar. 31, 2017
Earnings Per Share [Abstract]
Net Income (Loss) from Continuing Operations Available to Common Shareholders, Basic	$ 252	$ 213
Net Income (Loss) from Discontinued Operations Available to Common Shareholders, Basic	(2)	1
Net Income (Loss) Available to Common Stockholders, Basic	$ 250	$ 214
Weighted Average Number of Shares Outstanding, Basic	436,213	465,961
Weighted Average Number of Shares Outstanding, Diluted	438,931	466,829
Net Income (Loss) from Continuing Operations Available to Common Shareholders, Diluted	$ 252	$ 213
Net Income (Loss) from Discontinued Operations Available to Common Shareholders, Diluted	(2)	1
Net Income (Loss) Available to Common Stockholders, Diluted	$ 250	$ 214
Earnings Per Share, Basic [Abstract]
Income (Loss) from Continuing Operations, Per Basic Share	$ 0.58	$ 0.46
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share	(0.01)	0.00
Earnings Per Share, Basic	0.57	0.46
Earnings Per Share, Diluted [Abstract]
Income (Loss) from Continuing Operations, Per Diluted Share	0.57	0.46
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Diluted Share	(0.01)	0.00
Earnings Per Share, Diluted	$ 0.57	$ 0.46