Employee Benefits (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Pension plans
Components of net periodic (benefit) expense
Service cost	$ 15	$ 20	$ 32	$ 42
Interest cost	107	142	214	283
Expected return on plan assets	(183)	(223)	(367)	(449)
Recognition of prior service (credit) cost	(2)	2	(4)	3
Recognition of actuarial loss	45	42	87	80
Net periodic benefit (income) expense	(18)	(17)	(38)	(41)
Post-retirement benefit plans
Components of net periodic (benefit) expense
Service cost	5	6	10	12
Interest cost	27	35	55	70
Expected return on plan assets	(2)	(5)	(4)	(10)
Recognition of prior service (credit) cost	5	5	10	10
Net periodic benefit (income) expense	$ 35	$ 41	$ 71	$ 82