Pension and Other Postretirement Benefits (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 7	$ 7	$ 21	$ 23
Interest cost	39	38	117	112
Expected return on plan assets	(38)	(45)	(114)	(135)
Amortization of actuarial loss (gain)	23	24	69	72
Net periodic cost	31	24	93	72
Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0	0
Interest cost	4	3	11	11
Expected return on plan assets	0	0	0	0
Amortization of actuarial loss (gain)	(5)	(4)	(14)	(13)
Net periodic cost	$ (1)	$ (1)	$ (3)	$ (2)