Employee Benefit Plans (Net Periodic Benefit Cost) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Pension Benefits
Service cost	$ 35	$ 29
Interest cost	66	67
Expected return on plan assets	(114)	(108)
Amortization of prior service cost (credit)	1	1
Amortization of net loss	46	33
Net periodic benefit cost	34	22
Other Postretirement Benefits
Service cost	12	11
Interest cost	19	20
Expected return on plan assets	(22)	(21)
Amortization of prior service cost (credit)	(3)	(3)
Amortization of net loss	2	2
Net periodic benefit cost	$ 8	$ 9