Employee Benefits (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Pension Plans
Components of net periodic (benefit) expense
Service cost	$ 23	$ 23	$ 48	$ 45
Interest cost	135	156	270	312
Expected return on plan assets	(224)	(212)	(448)	(424)
Recognition of prior service cost	1	1	2	2
Recognition of actuarial loss	20	7	40	15
Net periodic benefit (income) expense	(45)	(25)	(88)	(50)
Post-Retirement Benefit Plans
Components of net periodic (benefit) expense
Service cost	6	5	12	11
Interest cost	35	44	70	87
Expected return on plan assets	(10)	(11)	(20)	(22)
Recognition of actuarial loss	1		2
Net periodic benefit (income) expense	$ 32	$ 38	$ 64	$ 76