Employee Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Pension Plans [Member]
Components of net periodic benefit cost:
Service cost	$ 35	$ 30
Interest cost	21	24
Expected return on plan assets	(44)	(42)
Amortization of:
Net actuarial (gain) loss	18	10
Prior service credit	(5)	(4)
Special charges	0	0
Net periodic benefit cost	25	18
Employee Benefit Plans (Textual)
Contributions to benefit plans	12	14
Future employer contributions to pension and other postretirement plans, as disclosed in annual report on Form 10-K			$ 140
Previously planned discretionary contributions subject to reconsideration	100
Other Postretirement Benefit Plans [Member]
Components of net periodic benefit cost:
Service cost	1	1
Interest cost	2	3
Expected return on plan assets	0	0
Amortization of:
Net actuarial (gain) loss	0	(1)
Prior service credit	(1)	(2)
Special charges	0	1
Net periodic benefit cost	2	2
Employee Benefit Plans (Textual)
Contributions to benefit plans	$ 4	$ 4
Future employer contributions to pension and other postretirement plans, as disclosed in annual report on Form 10-K			$ 21