Benefit Plans (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Pension benefits
Components of net periodic cost
Service cost	$ 24	$ 40
Interest cost	64	66
Expected return on plan assets	(99)	(97)
Amortization of prior service credit	(15)
Amortization of net actuarial loss (gain)	29	65
Settlement loss	11	10
Net periodic cost (credit)	14	84
Postretirement benefits
Components of net periodic cost
Service cost	3	4
Interest cost	6	8
Amortization of prior service credit	(6)	(6)
Amortization of net actuarial loss (gain)	(6)	(3)
Net periodic cost (credit)	$ (3)	$ 3