Stockholders' Equity (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	1 Months Ended	3 Months Ended	129 Months Ended	1 Months Ended
	Mar. 31, 2012	Jun. 30, 2001 June 2001 Buyback Plan [Member]	Mar. 31, 2011 June 2001 Buyback Plan [Member]	Mar. 31, 2012 June 2001 Buyback Plan [Member]	Apr. 30, 2011 April 2011 Buyback Plan [Member]
Prepayment for the repurchase of common stock	$ 400
Stock Repurchase Program, Authorized Amount		2,000			2,000
Stock Repurchased and Retired During Period, Shares			5.0	39.7
Stock Repurchased and Retired During Period, Value			$ 272	$ 1,884