Employee Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 3	$ 3	$ 5	$ 5
Interest cost	8	6	14	12
Expected return on plan assets	(10)	(12)	(20)	(22)
Net amortization	(1)	(3)	(3)	(6)
Net periodic benefit cost	0	(6)	(4)	(11)
Domestic Plan [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	4	5	8	10
Interest cost	28	26	55	52
Expected return on plan assets	(39)	(41)	(77)	(82)
Net amortization	7	7	16	15
Net periodic benefit cost	0	(3)	2	(5)
UNITED KINGDOM | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	4	5	8	10
Interest cost	13	14	26	28
Expected return on plan assets	(25)	(26)	(50)	(53)
Defined Benefit Plan, Accumulated Benefit Obligation, (Increase) Decrease for Settlement and Curtailment	0	24	0	24
Net amortization	9	14	18	29
Net periodic benefit cost	$ 1	$ 31	$ 2	$ 38