Employee Benefit Plans - Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
United States Pension Plan of US Entity [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Service Cost	$ 33	$ 36	$ 24
Defined Benefit Plan, Interest Cost	121	131	87
Defined Benefit Plan, Expected Return on Plan Assets	(169)	(164)	(119)
Defined Benefit Plan Net Amortization	53	44	58
Defined Benefit Plan, Net Periodic Benefit Cost	38	47	50
Domestic Other Postretirement Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Service Cost	11	14	14
Defined Benefit Plan, Interest Cost	31	46	33
Defined Benefit Plan, Expected Return on Plan Assets	(45)	(53)	(44)
Defined Benefit Plan Net Amortization	(11)	(3)	6
Defined Benefit Plan, Net Periodic Benefit Cost	(14)	4	9
UK Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Service Cost	24	24	22
Defined Benefit Plan, Interest Cost	79	95	85
Defined Benefit Plan, Expected Return on Plan Assets	(116)	(124)	(101)
Defined Benefit Plan Net Amortization	62	51	53
Defined Benefit Plan, Net Periodic Benefit Cost	$ 49	$ 46	$ 59