Computation of Basic/Diluted Earnings Per Common Share - Computation EPS (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Numerator:
Consolidated net income	$ 260	$ 188	$ 1,162	$ 858
Denominator:
Denominator for basic earnings per common share - weighted-average common shares outstanding (in shares)	763	755	761	753
Employee stock options and awards (in shares)	8	11	10	11
Denominator for diluted earnings per common share - weighted-average common shares outstanding plus dilutive common shares under treasury stock method (in shares)	771	766	771	764
Basic earnings per common share (in dollars per share)	$ 0.34	$ 0.25	$ 1.53	$ 1.14
Diluted earnings per common share (in dollars per share)	$ 0.34	$ 0.25	$ 1.51	$ 1.12