Computation of Basic/Diluted Earnings Per Common Share - Computation EPS (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Numerator:
Consolidated net income	$ 426	$ 363
Less: Distributed earnings to unvested share-based awards that participate in earnings	0	(2)
Less: Undistributed earnings allocated to unvested share-based awards that participate in earnings	0	(1)
Numerator for basic and diluted earnings per common share—income available to common shareholders	$ 426	$ 360
Denominator:
Denominator for basic earnings per common share - weighted-average common shares outstanding (in shares)	749	735
Effect of potential dilutive common shares under the treasury stock method:
Employee stock options and awards (in shares)	12	14
Denominator for diluted earnings per common share - weighted-average common shares outstanding plus dilutive common shares under treasury stock method (in shares)	761	749
Basic earnings (loss) per common share (in dollars per share)	$ 0.57	$ 0.49
Diluted earnings (loss) per common share (in dollars per share)	$ 0.56	$ 0.48