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, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share [Abstract]
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	$ 348	$ 254	$ 600	$ 467
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	1	(2)	(1)	(1)
Net Income (Loss) Attributable to Parent	$ 349	$ 252	$ 599	$ 466
Weighted Average Number of Shares Outstanding, Basic	430,628	457,891	433,405	461,904
Weighted Average Number of Shares Outstanding, Diluted	432,554	458,819	435,727	462,802
Earnings Per Share, Basic [Abstract]
Income (Loss) from Continuing Operations, Per Basic Share	$ 0.81	$ 0.55	$ 1.38	$ 1.01
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share	0.00	(0.01)	0.00	0.00
Earnings Per Share, Basic	0.81	0.55	1.38	1.01
Earnings Per Share, Diluted [Abstract]
Income (Loss) from Continuing Operations, Per Diluted Share	0.80	0.55	1.38	1.01
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Diluted Share	0.00	(0.01)	0.00	0.00
Earnings Per Share, Diluted	$ 0.81	$ 0.55	$ 1.37	$ 1.01