Employee Benefits (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Pension Plans
Components of net periodic benefit (income) expense
Service cost	$ 23	$ 21	$ 68	$ 49
Interest cost	156	166	468	395
Expected return on plan assets	(212)	(212)	(636)	(497)
Recognition of prior service cost	1		3
Recognition of net actuarial loss	7	4	22	11
Net periodic benefits (income) expense	(25)	(21)	(75)	(42)
Post-Retirement Plans
Components of net periodic benefit (income) expense
Service cost	5	5	16	12
Interest cost	44	49	131	104
Expected return on plan assets	(11)	(14)	(33)	(27)
Recognition of prior service cost				(1)
Net periodic benefits (income) expense	$ 38	$ 40	$ 114	$ 88