Employee Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Other Pension, Postretirement and Supplemental Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Prior Period Reclassification Adjustment	$ 4
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	2	$ 2
Interest cost	6	6
Expected return on plan assets	(10)	(10)
Net amortization	(3)	(3)
Net periodic benefit cost	(5)	(5)
Domestic Plan [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	5	6
Interest cost	26	29
Expected return on plan assets	(41)	(40)
Net amortization	8	7
Net periodic benefit cost	(2)	2
UNITED KINGDOM | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	5	6
Interest cost	14	14
Expected return on plan assets	(27)	(24)
Net amortization	15	17
Net periodic benefit cost	$ 7	$ 13