Income Taxes - Unrecognized Tax Benefits (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Income Tax Disclosure [Abstract]
Unrecognized tax benefits that was resolved favorably and reduced our effective tax rate	$ 0		$ 0		$ 60
Accrued interest payable related to unrecognized tax benefits	0		0		5
Interest expense related to unrecognized tax benefits	0		0		2
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits as of January 1	758	[1]	864	[1]	911
Gross increases—tax positions in prior years	0		1		83
Gross decreases—tax positions in prior years	(110)		(2)		(31)
Settlements	0		(105)		(99)
Unrecognized tax benefits as of December 31	648	[1]	758	[1]	864	[1]
Unrecognized tax benefits resulting in net operating loss carryforward	$ 648		$ 758		$ 804

[1] Amounts exclude tax credits and net operating losses of $648 million, $758 million and $804 million as of December 31, 2012, 2011 and 2010, respectively.