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 (income):
Service cost	$ 13	$ 15	$ 43	$ 44
Interest cost	83	97	250	293
Expected return on plan assets	(149)	(144)	(447)	(432)
Recognition of actuarial loss	2	0	5	0
Net periodic benefit (income) expense	(51)	(32)	(149)	(95)
Post-Retirement Benefit Plans
Components of net periodic benefit expense (income):
Service cost	3	2	9	6
Interest cost	30	37	88	110
Expected return on plan assets	(9)	(10)	(27)	(31)
Recognition of actuarial loss	1	0	3	0
Net periodic benefit (income) expense	$ 25	$ 29	$ 73	$ 85