Employee Benefits (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Pension plans
Components of net periodic (benefit) expense
Service cost	$ 19	$ 23	$ 39	$ 48
Interest cost	151	135	302	270
Expected return on plan assets	(223)	(224)	(446)	(448)
Recognition of prior service cost	3	1	4	2
Recognition of actuarial loss	5	20	10	40
Net periodic benefit (income) expense	(45)	(45)	(91)	(88)
Post-retirement benefit plans
Components of net periodic (benefit) expense
Service cost	5	6	11	12
Interest cost	40	35	79	70
Expected return on plan assets	(8)	(10)	(16)	(20)
Recognition of prior service cost	5	0	9	0
Recognition of actuarial loss	0	1	0	2
Net periodic benefit (income) expense	$ 42	$ 32	$ 83	$ 64