Employee Retirement Plans (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Pension [Member]
Components of net pension and postretirement benefits costs
Service cost of benefits earned	$ 10	$ 8	$ 29	$ 23
Interest cost on projected benefit obligation	16	16	47	48
Expected return on plan assets	(19)	(18)	(57)	(52)
Net amortization	11	9	34	26
Net cost	18	15	53	45
Postretirement [Member]
Components of net pension and postretirement benefits costs
Service cost of benefits earned	1	1	3	3
Interest cost on projected benefit obligation	2	2	5	6
Net amortization	(9)	(9)	(26)	(27)
Net cost	$ (6)	$ (6)	$ (18)	$ (18)