Employee Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Pension Plans [Member]
Components of net periodic benefit cost:
Service cost	$ 30	$ 33	$ 60	$ 67
Interest cost	25	23	49	46
Expected return on plan assets	(41)	(41)	(83)	(82)
Amortization of:
Net actuarial (gain) loss	10	17	20	33
Prior service credit	(5)	(4)	(9)	(9)
Special charges	2	3	2	5
Net periodic benefit cost	21	31	39	60
Employee Benefit Plans (Textual)
Future employer contributions to pension and other postretirement plans					$ 35
Contributions to benefit plans			23	16
Other Postretirement Benefit Plans [Member]
Components of net periodic benefit cost:
Service cost	1	2	2	3
Interest cost	3	3	6	5
Expected return on plan assets	0	0	0	0
Amortization of:
Net actuarial (gain) loss	(1)	(1)	(2)	(1)
Prior service credit	(2)	(3)	(4)	(6)
Special charges	0	0	1	0
Net periodic benefit cost	$ 1	$ 1	3	1
Employee Benefit Plans (Textual)
Future employer contributions to pension and other postretirement plans					$ 21
Contributions to benefit plans			$ 8	$ 9