Employee Benefits (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Pension plans
Components of net periodic (benefit) expense
Service cost	$ 17	$ 22
Interest cost	107	141
Expected return on plan assets	(184)	(226)
Recognition of prior service (credit) cost	(2)	1
Recognition of actuarial loss	42	38
Net periodic benefit (income) expense	(20)	(24)
Post-retirement benefit plans
Components of net periodic (benefit) expense
Service cost	5	6
Interest cost	28	35
Expected return on plan assets	(2)	(5)
Recognition of prior service (credit) cost	5	5
Net periodic benefit (income) expense	$ 36	$ 41