Employee Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Pension Plans [Member]
Components of net periodic benefit cost:
Service cost	$ 30	$ 34
Interest cost	24	23
Expected return on plan assets	(42)	(41)
Amortization of:
Net actuarial (gain) loss	10	16
Prior service credit	(4)	(5)
Special charges	0	2
Net periodic benefit cost	18	29
Employee Benefit Plans (Textual)
Future employer contributions to pension and other postretirement plans	35
Contributions to benefit plans	14	8
Other Postretirement Benefit Plans [Member]
Components of net periodic benefit cost:
Service cost	1	1
Interest cost	3	2
Expected return on plan assets	0	0
Amortization of:
Net actuarial (gain) loss	(1)	0
Prior service credit	(2)	(3)
Special charges	1	0
Net periodic benefit cost	2	0
Employee Benefit Plans (Textual)
Future employer contributions to pension and other postretirement plans	21
Contributions to benefit plans	$ 4	$ 4