Computation of Basic/Diluted Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Numerator:
Consolidated net income	$ 212	$ 204	$ 606	$ 497
Less: Distributed earnings to unvested stock-based awards that participate in earnings	0	0	(4)	(5)
Less: Undistributed earnings allocated to unvested stock-based awards that participate in earnings	(2)	(4)	(5)	(8)
Numerator for basic and diluted earnings per common share — income available to common shareholders	$ 210	$ 200	$ 597	$ 484
Denominator:
Denominator for basic earnings per common share - weighted-average common shares outstanding (in shares)	727	716	725	712
Effect of potential dilutive common shares under the treasury stock method:
Employee stock options and awards (in shares)	8	9	9	11
Denominator for diluted earnings per common share - weighted-average common shares outstanding plus dilutive common shares under treasury stock method (in shares)	735	725	734	723
Basic earnings per common share (in dollars per share)	$ 0.29	$ 0.28	$ 0.82	$ 0.68
Diluted earnings per common share (in dollars per share)	$ 0.29	$ 0.28	$ 0.81	$ 0.67
Common stock weighted-average shares, unvested restricted stock rights (in shares)	9	16	10	16
Performance shares not included in the computation of EPS	3	3	3	3
Options
Antidilutive [Line Items]
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	1	2	6	3