Share Repurchase Authorization (details) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Share Repurchase Authorization disclosure
Share repurchase authorization, number of shares repurchased (in shares)	6.0	18.9
Share repurchase authorization, cost of shares repurchased	$ 350,000,000	$ 1,100,000,000
Share repurchase authorization, average cost per share repurchased	$ 58.73
Share repurchase authorization, remaining capacity under share repurchase authorization	$ 3,260,000,000