Employee Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 3	$ 2	$ 7	$ 7
Interest cost	7	7	21	23
Expected return on plan assets	(9)	(10)	(30)	(31)
Net amortization	(3)	(2)	(10)	(9)
Net periodic benefit cost	(2)	(3)	(12)	(10)
Domestic Plan [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	6	7	18	22
Interest cost	29	31	87	94
Expected return on plan assets	(40)	(39)	(120)	(120)
Net amortization	7	12	22	36
Net periodic benefit cost	2	11	7	32
UNITED KINGDOM | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	6	5	19	16
Interest cost	15	17	44	55
Expected return on plan assets	(25)	(27)	(74)	(85)
Defined Benefit Plan, Plan Assets, Payment for Settlement	18	0	18	0
Net amortization	17	11	50	34
Net periodic benefit cost	$ 31	$ 6	$ 57	$ 20