Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Pension benefits
Components of net periodic cost
Service cost	$ 28	$ 24	$ 57	$ 48
Interest cost	64	64	128	128
Expected return on plan assets	(106)	(100)	(212)	(199)
Amortization of prior service credit	(14)	(14)	(28)	(29)
Amortization of net actuarial loss (gain)	48	28	96	57
Settlement loss	6	11	12	22
Net periodic postretirement cost (credit)	26	13	53	27
Postretirement benefits
Components of net periodic cost
Service cost	3	2	6	5
Interest cost	5	5	11	11
Amortization of prior service credit	(5)	(5)	(11)	(11)
Amortization of net actuarial loss (gain)	(2)	(5)	(4)	(11)
Net periodic postretirement cost (credit)	$ 1	$ (3)	$ 2	$ (6)