Employee Benefits (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Pension plans
Employee Benefits
Pension contributions	$ 100
Components of net periodic (benefit) expense
Service cost	20	$ 19	$ 62	$ 58
Interest cost	142	151	425	453
Expected return on plan assets	(224)	(223)	(673)	(669)
Recognition of prior service cost	1	1	4	5
Recognition of actuarial loss	40	5	120	15
Net periodic benefit (income) expense	(21)	(47)	(62)	(138)
Post-retirement benefit plans
Components of net periodic (benefit) expense
Service cost	6	5	18	16
Interest cost	35	40	105	119
Expected return on plan assets	(6)	(8)	(16)	(24)
Recognition of prior service cost	6	4	16	13
Net periodic benefit (income) expense	$ 41	$ 41	$ 123	$ 124