Employee Separation Charges (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
Mar. 31, 2013	Dec. 31, 2012
Employee Separation Charges [Roll Forward]
Liability balance at beginning of period	$ 29	$ 90
Increase in liability (separation charges)	7	94
Reduction in liability (payments and other adjustments)	(11)	(155)
Liability balance at end of period	$ 25	$ 29

The charge against earnings in the period for known and estimated costs of termination benefits provided to current employees that are involuntarily terminated under a benefit arrangement associated with exit from or disposal of business activities or restructurings pursuant to a duly authorized plan, excluding costs or losses pertaining to an entity newly acquired in a business combination or a discontinued operation as defined by generally accepted accounting principles and costs associated with one-time termination benefits.

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