Computation of Earnings (Loss) Per Basic/Diluted Common Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Numerator:
Consolidated net income (loss)	$ 354	$ 226	$ 185	$ 384	$ 99	$ 148	$ 335	$ 503	$ 1,149	$ 1,085	$ 418
Less: Distributed earnings to unvested share-based awards that participate in earnings									(4)	(3)	(2)
Less: Undistributed earnings allocated to unvested share-based awards that participate in earnings									(20)	(13)	(2)
Numerator for basic earnings per common share-income (loss) available to common shareholders									$ 1,125	$ 1,069	$ 414
Denominator:
Denominator for basic earnings per common share - weighted-average common shares outstanding (in shares)									1,112	1,148	1,222
Effect of potential dilutive common shares under the treasury stock method:
Employee stock options (in shares)									6	8	14
Denominator for diluted earnings per common share - weighted-average common shares outstanding plus dilutive effect of employee stock options (in shares)									1,118	1,156	1,236
Basic earnings per common share (in dollars per share)	$ 0.31	$ 0.20	$ 0.16	$ 0.34	$ 0.09	$ 0.13	$ 0.29	$ 0.42	$ 1.01	$ 0.93	$ 0.34
Diluted earnings per common share (in dollars per share)	$ 0.31	$ 0.20	$ 0.16	$ 0.33	$ 0.08	$ 0.13	$ 0.29	$ 0.42	$ 1.01	$ 0.92	$ 0.33
Common stock weighted-average shares, unvested restricted stock rights (in shares)									24	17
Antidilutive securities excluded from computation of diluted earnings per share (in shares)									25	25	25