Commitments and Contingencies - Environmental (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Loss Contingencies [Line Items]
Accrued obligations for environmental matters, current liabilities	$ 60
Site Contingency, Estimated Time Frame for Accrued Cost Distributions	10 years
Accrual for Environmental Loss Contingencies [Roll Forward]
Beginning balance	404	435
Accruals	1	2
Payments	(10)	(10)
Ending balance	395	427
Environmental Issue
Loss Contingencies [Line Items]
Number of alleged environmental contamination sites (in sites)	225
Number of environmental superfund sites (in sites)	16
Liability for third-party tort claims	13		15
Future costs for environmental liabilities, minimum	295
Future costs for environmental liabilities, maximum	$ 530