Employee Benefits (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 Plans
Components of net periodic (benefit) expense
Service cost	$ 22	$ 23	$ 70	$ 68
Interest cost	137	156	407	468
Expected return on plan assets	(224)	(212)	(672)	(636)
Recognition of prior service cost	1	1	4	3
Recognition of actuarial loss	20	7	61	22
Net periodic benefit (income) expense	(44)	(25)	(130)	(75)
Post-Retirement Benefit Plans
Components of net periodic (benefit) expense
Service cost	6	5	18	16
Interest cost	35	44	105	131
Expected return on plan assets	(10)	(11)	(30)	(33)
Recognition of actuarial loss	1	0	3	0
Net periodic benefit (income) expense	$ 32	$ 38	$ 96	$ 114