Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Basic EPS
Net Income	$ 631	$ 708
Less: Net income allocated to participating securities	(3)	(3)
Net Income, net of participating securities	$ 628	$ 705
Weighted average number of basic shares (in shares)	748.9	765.6
Basic EPS (in dollars per share)	$ 0.84	$ 0.92
Diluted EPS
Net income, net of participating securities	$ 628	$ 705
Weighted average number of basic shares (in shares)	748.9	765.6
Dilutive effect of potentially dilutive securities (in shares)	1.6	1.4
Total diluted weighted average common shares (in shares)	750.5	767.0
Diluted EPS (in dollars per share)	$ 0.84	$ 0.92