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 (income):
Service cost	$ 14	$ 15	$ 30	$ 29
Interest cost	83	97	167	196
Expected return on plan assets	(149)	(144)	(298)	(288)
Recognition of actuarial loss	2		3
Net periodic benefit (income) expense	(50)	(32)	(98)	(63)
Post-Retirement Benefit Plans
Components of net periodic benefit expense (income):
Service cost	3	2	6	4
Interest cost	29	37	58	73
Expected return on plan assets	(9)	(10)	(18)	(21)
Recognition of actuarial loss	1		2
Net periodic benefit (income) expense	$ 24	$ 29	$ 48	$ 56