Employee Benefits (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Pension plans
Components of net periodic (benefit) expense
Service cost	$ 20	$ 19	$ 42	$ 39
Interest cost	142	151	283	302
Expected return on plan assets	(223)	(223)	(449)	(446)
Recognition of prior service cost	2	3	3	4
Recognition of actuarial loss	42	5	80	10
Net periodic benefit (income) expense	(17)	(45)	(41)	(91)
Post-retirement benefit plans
Components of net periodic (benefit) expense
Service cost	6	5	12	11
Interest cost	35	40	70	79
Expected return on plan assets	(5)	(8)	(10)	(16)
Recognition of prior service cost	5	5	10	9
Net periodic benefit (income) expense	$ 41	$ 42	$ 82	$ 83