Employee Benefits (Details 3) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Pension Benefits [Member]
Components of net pension and other postretirement benefit costs reflected in net income [Abstract]
Service cost	$ 79	$ 75	$ 73
Interest cost	120	112	104
Expected return on plan assets	(140)	(131)	(118)
Amortization of net actuarial loss and prior service cost and other	68	64	46
Total benefit costs reflected in net income	127	120	105
Other Postretirement Benefits [Member]
Components of net pension and other postretirement benefit costs reflected in net income [Abstract]
Service cost	11	11	10
Interest cost	22	21	19
Expected return on plan assets	(5)	(4)	(4)
Amortization of net actuarial loss and prior service cost and other	3	2	1
Total benefit costs reflected in net income	$ 31	$ 30	$ 26