Employee Benefits (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Pension plans
Components of net periodic (benefit) expense
Service cost	$ 14	$ 17	$ 28	$ 33
Interest cost	107	96	217	196
Expected return on plan assets	(153)	(169)	(309)	(342)
Recognition of prior service credit	(2)	(2)	(4)	(4)
Recognition of actuarial loss	56	45	113	89
Net periodic pension benefit expense (income)	22	(13)	45	(28)
Post-retirement benefit plans
Components of net periodic (benefit) expense
Service cost	4	5	8	9
Interest cost	28	25	55	49
Recognition of prior service credit	4	5	8	10
Net periodic pension benefit expense (income)	$ 36	$ 35	$ 71	$ 68