Equity (Narrative) (USD $) Share data in Millions, unless otherwise specified	3 Months Ended	1 Months Ended		12 Months Ended
	Mar. 31, 2012	Nov. 30, 2011 Accelerated Share Repurchase Program [Member]	May 31, 2011 Accelerated Share Repurchase Program [Member]	Dec. 31, 2011 Accelerated Share Repurchase Program [Member]
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, authorized amount	$ 1,000,000,000
Payments for the acquisition of common stock				$ 500,000,000
Treasury stock, shares acquired		9.3	19.9