Computation of Basic/Diluted Earnings Per Common Share - Computation EPS (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Numerator:
Consolidated net income	$ 328	$ 447	$ 402	$ 500	$ 774	$ 902
Denominator:
Denominator for basic earnings per common share - weighted-average common shares outstanding (in shares)	766		761		765	760
Employee stock options and awards (in shares)	4		9		5	10
Denominator for diluted earnings per common share - weighted-average common shares outstanding plus dilutive common shares under treasury stock method (in shares)	770		770		770	770
Basic earnings per common share (in dollars per share)	$ 0.43		$ 0.53		$ 1.01	$ 1.19
Diluted earnings per common share (in dollars per share)	$ 0.43		$ 0.52		$ 1.01	$ 1.17