Employment Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Transition period	10 years
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Curtailment gain as a result of plan amendments	$ 120
Service cost	10	$ 11
Interest cost	22	21
Expected return on plan assets	(39)	(40)
Amortization of net gain	1	0
Amortization of prior service credits	(3)	0
Curtailment gain	117	0
Net cost recognized	(128)	(8)
Retiree Health and Welfare Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	2	2
Net cost recognized	$ 2	$ 2