Shareholders' Equity (details) (USD $)	3 Months Ended	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2012	Sep. 30, 2011	Jun. 07, 2011
Shareholders' Equity disclosure
Share repurchase authorization, number of shares repurchased (in shares)	5,400,000	17,000,000	30,100,000
Share repurchase authorization, cost of shares repurchased	$ 350,000,000	$ 1,050,000,000	$ 1,712,000,000
Share repurchase authorization, average cost per share repurchased	$ 65.00	$ 61.93
Share repurchase authorization, remaining capacity under share repurchase authorization		$ 2,560,000,000
Number of common shares issued upon conversion of preferred shares, per preferred share				8
Preferred shares outstanding				190,083
Number of common shares issued upon conversion of preferred shares, total				1,520,000