Employee Retirement Plans (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		1 Months Ended	3 Months Ended
	Mar. 31, 2012 Pension [Member]	Mar. 31, 2011 Pension [Member]	Apr. 30, 2012 Pension [Member] Canada [Member]	Mar. 31, 2012 Pension [Member] Canada [Member]	Mar. 31, 2012 Postretirement [Member]	Mar. 31, 2011 Postretirement [Member]
Components of net pension and postretirement benefits costs
Service cost of benefits earned	$ 8	$ 7			$ 1	$ 2
Interest cost on projected benefit obligation	16	16			2	4
Expected return on plan assets	(17)	(16)
Net amortization	9	6			(9)	(6)
Net cost	16	13			(6)
Employee Retirement Plans (Textual) [Abstract]
Contribution by employer	$ 66		$ 7	$ 2