Employee Retirement Plans (Employee Retirement Plans) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Defined Benefit Plan Disclosure [Line Items]
Cap on contribution toward future retiree medical coverage	120.00%		120.00%
Percent employees will pay for retiree medical	100.00%		100.00%
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 13	$ 11	$ 40	$ 34
Interest cost	39	39	116	116
Expected return on plan assets	(41)	(42)	(122)	(126)
Amortization of net loss	20	12	57	37
Amortization of prior service cost	2	2	6	7
Total pension and postretirement benefit expense	33	22	97	68
Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	3	2	11	9
Interest cost	12	13	36	38
Amortization of net loss	4	3	13	12
Amortization of prior service cost	(1)	(1)	(4)	(5)
Total pension and postretirement benefit expense	$ 18	$ 17	$ 56	$ 54