Employee Benefits (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Pension plans
Components of net periodic (benefit) expense
Service cost	$ 14	$ 17	$ 42	$ 50
Interest cost	109	99	326	295
Expected return on plan assets	(155)	(171)	(464)	(513)
Recognition of prior service credit	(2)	(2)	(6)	(6)
Recognition of actuarial loss	54	45	167	134
Net periodic pension benefit expense (income)	20	(12)	65	(40)
Post-retirement benefit plans
Components of net periodic (benefit) expense
Service cost	3	4	11	13
Interest cost	27	24	82	73
Expected return on plan assets	0	(1)	0	(1)
Recognition of prior service credit	5	5	13	15
Net periodic pension benefit expense (income)	$ 35	$ 32	$ 106	$ 100