Equity (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011
Share repurchases
Average price paid per share	$ 50.35	[1]	$ 39.40	[1]	$ 50.35	[1]	$ 39.20	[1]
Average price paid per share excluding period shares repurchased	$ 49.99
Total cash utilized	$ 295	[1]	$ 355	[1]	$ 295	[1]	$ 655	[1]
Stock Repurchased During Period, Shares	0.5
Stock Repurchased During Period, Value	$ 25.6
2011 Repurchase Program [Member]
Share repurchases
Total number of shares purchased	5.9	[1],[2]	8.3	[1],[2]	6.8	[1],[2]	8.3	[1],[2]
2007 Repurchase Program [Member]
Share repurchases
Total number of shares purchased	0		0.7		0		8.4

[1] In any period, cash used in financing activities related to common stock repurchased may differ from the comparable change in equity, reflecting timing differences between the recognition of share repurchase transactions and their settlement for cash. As such, in the third quarter of 2012, 0.5 million shares were repurchased for $25.6 million, which settled in October 2012. Excluding these 0.5 million shares, the average price paid per share was $49.99.

[2] For the nine months ended September 30, 2012, includes shares received at the conclusion of the uncollared Accelerated Share Repurchase Agreement described in more detail below.