Employee Retirement Plans (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Pension [Member]
Components of net pension and postretirement benefits costs
Service cost of benefits earned	$ 10	$ 8
Interest cost on projected benefit obligation	16	16
Defined Benefit Plan, Expected Return on Plan Assets	(19)	(17)
Defined Benefit Plan, Amortization of Gains (Losses)	11	9
Net cost	18	16
Postretirement [Member]
Components of net pension and postretirement benefits costs
Service cost of benefits earned	1	1
Interest cost on projected benefit obligation	2	2
Defined Benefit Plan, Amortization of Gains (Losses)	(9)	(9)
Net cost	$ (6)	$ (6)