Employee Benefit Plans - Net Periodic Benefit Cost (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Domestic Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	$ 36	$ 24	$ 25
Interest Cost	131	87	98
Expected Return on Plan Assets	(164)	(119)	(119)
Net Amortization	44	58	37
Net Periodic Benefit Cost	47	50	41
Domestic Other Postretirement Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	14	14	11
Interest Cost	46	33	36
Expected Return on Plan Assets	(53)	(44)	(43)
Net Amortization	(3)	6	1
Net Periodic Benefit Cost	4	9	5
UK Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	24	22	19
Interest Cost	95	85	85
Expected Return on Plan Assets	(124)	(101)	(104)
Net Amortization	51	53	43
Net Periodic Benefit Cost	$ 46	$ 59	$ 43