Employee Benefit Plans (Net Periodic Benefit Cost) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 29	$ 35
Interest cost	72	66
Expected return on plan assets	(125)	(114)
Amortization of prior service cost (credit)	1	1
Amortization of net loss	28	46
Net periodic benefit cost (credit)	5	34
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	8	12
Interest cost	17	19
Expected return on plan assets	(28)	(22)
Amortization of prior service cost (credit)	(7)	(3)
Amortization of net loss	0	2
Net periodic benefit cost (credit)	$ (10)	$ 8