Long-Term Debt and Credit Facility (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Aug. 31, 2012	Dec. 31, 2011
Summary of debt
Total	$ 1,700		$ 1,200
Unaccreted discount	(7)		(4)
Total	1,693		1,196
Fixed interest rate on senior note		2.50%
1.500% Fixed Rate Notes Due 2013 [Member]
Summary of debt
Total	300		300
Fixed interest rate on senior note	1.50%
2.375% Fixed Rate Notes Due 2015 [Member]
Summary of debt
Total	400		400
Fixed interest rate on senior note	2.375%
2.700% Fixed Rate Notes Due 2018 [Member]
Summary of debt
Total	500		500
Fixed interest rate on senior note	2.70%
2.500% Fixed Rate Notes Due 2022 [Member]
Summary of debt
Total	$ 500		$ 0
Fixed interest rate on senior note	2.50%