Employee Pension and Other Postretirement Benefits (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Pension Benefits
Components of net periodic benefit cost:
Service cost	$ 19	$ 19
Interest cost	29	25
Expected return on plan assets	(64)	(67)
Amortization of prior service credit	(6)	(6)
Recognized net actuarial loss	15	22
Total net periodic benefit (income) cost	(7)	(7)
Other Postretirement Benefits
Components of net periodic benefit cost:
Service cost	1	1
Interest cost	2	2
Expected return on plan assets	(4)	(5)
Amortization of prior service credit	(4)	(4)
Recognized net actuarial loss	2	1
Total net periodic benefit (income) cost	(3)	(5)
Superannuation Supplemental Executives Retirement Plan Defined Benefit and Executive Supplemental Defined Benefit Plan [Member]
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
Superannuation, SERP and ESBP
Components of net periodic benefit cost:
Total net periodic benefit (income) cost	$ 2	$ 2