Employee Benefits (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Combined Pension Plan
Components of net periodic (benefit) expense
Service cost	$ 13	$ 14	$ 29	$ 28
Interest cost	80	107	162	217
Expected return on plan assets	(149)	(153)	(298)	(309)
Recognition of prior service credit	(1)	(2)	(4)	(4)
Recognition of actuarial loss	52	56	102	113
Net periodic pension benefit (income) expense	(5)	22	(9)	45
Post-Retirement Benefit Plans
Components of net periodic (benefit) expense
Service cost	3	4	7	8
Interest cost	20	28	40	55
Recognition of prior service credit	4	4	8	8
Net periodic pension benefit (income) expense	$ 27	$ 36	$ 55	$ 71