Employee Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1	$ 3	$ 6	$ 7
Interest cost	7	7	19	21
Expected return on plan assets	(9)	(9)	(31)	(30)
Net amortization	(3)	(3)	(9)	(10)
Net periodic benefit cost	(4)	(2)	(15)	(12)
Domestic Plan [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	5	6	15	18
Interest cost	26	29	78	87
Expected return on plan assets	(41)	(40)	(123)	(120)
Net amortization	8	7	23	22
Net periodic benefit cost	(2)	2	(7)	7
UNITED KINGDOM | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	5	6	15	19
Interest cost	14	15	42	44
Expected return on plan assets	(25)	(25)	(78)	(74)
Defined Benefit Plan, Plan Assets, Payment for Settlement	12	18	36	18
Net amortization	9	17	38	50
Net periodic benefit cost	15	$ 31	53	$ 57
Accounting Standards Update 2017-07 [Member] | Other Pension, Postretirement and Supplemental Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Prior Period Reclassification Adjustment	$ 16		$ 8