Restructuring Charges (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended		27 Months Ended
	Mar. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Mar. 31, 2012
Restructuring And Related Cost [Line Items]
Restructuring charges		$ 46	$ 81
Cumulative amount paid since restructuring activities began	10			85
Severance Costs [Member]
Restructuring And Related Cost [Line Items]
Restructuring charges		12	66
Cumulative amount paid since restructuring activities began				67
Contract Termination And Other Associated Costs [Member]
Restructuring And Related Cost [Line Items]
Restructuring charges		34	15
Cumulative amount paid since restructuring activities began				$ 18