Restructuring Charges (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended		27 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Mar. 31, 2013
Restructuring And Related Cost [Line Items]
Restructuring charges		$ 19	$ 43
Cumulative amount paid since restructuring activities began	9			36
Severance Costs [Member]
Restructuring And Related Cost [Line Items]
Restructuring charges		13	9
Cumulative amount paid since restructuring activities began				18
Contract Termination And Other Associated Costs [Member]
Restructuring And Related Cost [Line Items]
Restructuring charges		6	34
Cumulative amount paid since restructuring activities began				$ 18