Computation of Basic/Diluted Earnings Per Common Share (Details) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Numerator:
Consolidated net income (loss)	$ 324,000,000	$ 185,000,000	$ 780,000,000	$ 569,000,000
Less: Distributed earnings to unvested share-based awards that participate in earnings	0	0	(4,000,000)	(4,000,000)
Less: Undistributed earnings allocated to unvested share-based awards that participate in earnings	(6,000,000)	(4,000,000)	(12,000,000)	(7,000,000)
Numerator for basic earnings per common share-income (loss) available to common shareholders	$ 318,000,000	$ 181,000,000	$ 764,000,000	$ 558,000,000
Denominator:
Denominator for basic earnings per common share - weighted-average common shares outstanding (in shares)	1,118	1,109	1,116	1,115
Effect of potential dilutive common shares under the treasury stock method:
Employee stock options (in shares)	9	6	8	6
Denominator for diluted earnings per common share - weighted-average common shares outstanding plus dilutive effect of employee stock options (in shares)	1,127	1,115	1,124	1,121
Basic earnings per common share (in dollars per share)	$ 0.28	$ 0.16	$ 0.68	$ 0.50
Diluted earnings per common share (in dollars per share)	$ 0.28	$ 0.16	$ 0.68	$ 0.50
Common stock weighted-average shares, unvested restricted stock rights (in shares)	24	24	25	22
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	8	20	9	20