Employee Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Pension Plans [Member]
Components of net periodic benefit cost:
Service cost	$ 40	$ 35
Interest cost	18	21
Expected return on plan assets	(48)	(44)
Amortization of:
Net actuarial loss	20	18
Prior service credit	(4)	(5)
Net periodic benefit cost	26	25
Employee Benefit Plans (Textual)
Future employer contributions to pension and other postretirement plans, as disclosed in annual report on Form 10-K			$ 128
Contributions to benefit plans	21	12
Other Postretirement Benefit Plans [Member]
Components of net periodic benefit cost:
Service cost	2	1
Interest cost	2	2
Expected return on plan assets	0	0
Amortization of:
Net actuarial loss	0	0
Prior service credit	(2)	(1)
Net periodic benefit cost	2	2
Employee Benefit Plans (Textual)
Future employer contributions to pension and other postretirement plans, as disclosed in annual report on Form 10-K			$ 22
Contributions to benefit plans	$ 3	$ 4