Commitments and Contingencies - Environmental (Details) - Environmental Issue $ in Millions	3 Months Ended
	Mar. 31, 2016 USD ($) sites	Mar. 31, 2015 USD ($)	Dec. 31, 2015 USD ($)
Loss Contingencies [Line Items]
Number of alleged environmental contamination sites (in sites) | sites	221
Number of environmental superfund sites (in sites) | sites	18
Liability for third-party tort claims	$ 12		$ 12
Site Contingency, Estimated Time Frame for Accrued Cost Distributions	10 years
Accrual for Environmental Loss Contingencies [Roll Forward]
Beginning balance	$ 369	$ 404
Accruals	0	1
Payments	(7)	(10)
Ending balance	362	$ 395
Minimum [Member]
Loss Contingencies [Line Items]
Loss Contingency, Estimate of Possible Loss	280
Maximum [Member]
Loss Contingencies [Line Items]
Loss Contingency, Estimate of Possible Loss	490
Current Liabilities [Member]
Loss Contingencies [Line Items]
Accrued obligations for environmental matters, current liabilities	$ 50		$ 50