Pension and Other Postretirement 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
Components Of Net Periodic Cost Details [Abstract]
Pension contribution			$ 150
Pension Benefits [Member]
Components Of Net Periodic Cost Details [Abstract]
Service cost	10	9	20	18
Interest cost	53	61	106	122
Expected return on plan assets	(68)	(62)	(136)	(124)
Amortization of actuarial loss (gain)	22	18	44	36
Net periodic cost	17	26	34	52
Postretirement Benefits [Member]
Components Of Net Periodic Cost Details [Abstract]
Service cost	0	0	0	0
Interest cost	6	8	12	16
Expected return on plan assets	0	0	0	0
Amortization of actuarial loss (gain)	(4)	(4)	(8)	(8)
Net periodic cost	$ 2	$ 4	$ 4	$ 8