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, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Numerator:
Consolidated net income	$ 204	$ 328	$ 447	$ 260	$ 402	$ 500	$ 978	$ 1,162
Denominator:
Denominator for basic earnings per common share - weighted-average common shares outstanding (in shares)	767			763			766	761
Employee stock options and awards (in shares)	4			8			4	10
Denominator for diluted earnings per common share - weighted-average common shares outstanding plus dilutive common shares under treasury stock method (in shares)	771			771			770	771
Basic earnings per common share (in dollars per share)	$ 0.27			$ 0.34			$ 1.28	$ 1.53
Diluted earnings per common share (in dollars per share)	$ 0.26			$ 0.34			$ 1.27	$ 1.51