Benefit Plans (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Pension benefits
Components of net periodic cost
Service cost	$ 24	$ 39	$ 48	$ 79
Interest cost	64	66	128	132
Expected return on plan assets	(100)	(96)	(199)	(193)
Amortization of prior service credit	(14)	(1)	(29)	(1)
Amortization of net actuarial loss (gain)	28	65	57	130
Settlement loss	11	9	22	19
Net periodic cost (credit)	13	82	27	166
Postretirement benefits
Components of net periodic cost
Service cost	2	3	5	7
Interest cost	5	9	11	17
Amortization of prior service credit	(5)	(6)	(11)	(12)
Amortization of net actuarial loss (gain)	(5)	(3)	(11)	(6)
Net periodic cost (credit)	$ (3)	$ 3	$ (6)	$ 6