Employee Pension and Other Postretirement Benefits (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Pension Benefits
Components of net periodic benefit cost:
Service cost	$ 20	$ 19	$ 63	$ 57
Interest cost	23	29	71	88
Expected return on plan assets	(67)	(64)	(200)	(193)
Amortization of prior service credit	(5)	(7)	(19)	(20)
Recognized net actuarial loss	26	15	80	46
Total net periodic benefit (income) cost	(3)	(8)	(5)	(22)
Other Postretirement Benefits
Components of net periodic benefit cost:
Service cost	0	1	1	2
Interest cost	2	2	5	7
Expected return on plan assets	(5)	(4)	(15)	(13)
Amortization of prior service credit	(1)	(3)	(1)	(10)
Recognized net actuarial loss	1	2	1	7
Total net periodic benefit (income) cost	(3)	(2)	(9)	(7)
Superannuation Supplemental Executives Retirement Plan Defined Benefit and Executive Supplemental Defined Benefit Plan
Components of net periodic benefit cost:
Service cost			0	0
Interest cost			2	3
Expected return on plan assets			0	0
Amortization of prior service credit			0	0
Recognized net actuarial loss			3	2
Superannuation, SERP and ESBP
Components of net periodic benefit cost:
Service cost	0	0
Interest cost	1	1
Expected return on plan assets	0	0
Amortization of prior service credit	0	0
Recognized net actuarial loss	1	1
Total net periodic benefit (income) cost	$ 2	$ 2	$ 5	$ 5