Commitments and Contingencies - Environmental (Details) - Environmental Issue $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016 USD ($) sites	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($) sites	Jun. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Loss Contingencies [Line Items]
Number of alleged environmental contamination sites (in sites) | sites	216		216
Number of environmental superfund sites (in sites) | sites	18		18
Liability for third-party tort claims	$ 12		$ 12		$ 12
Site Contingency, Estimated Time Frame for Accrued Cost Distributions			10 years
Accrual for Environmental Loss Contingencies [Roll Forward]
Beginning balance	362	$ 395	$ 369	$ 404
Accruals	0	2	0	3
Payments	(7)	(9)	(14)	(19)
Ending balance	355	$ 388	355	$ 388
Minimum [Member]
Loss Contingencies [Line Items]
Loss Contingency, Estimate of Possible Loss	275		275
Maximum [Member]
Loss Contingencies [Line Items]
Loss Contingency, Estimate of Possible Loss	485		485
Current Liabilities [Member]
Loss Contingencies [Line Items]
Accrued obligations for environmental matters, current liabilities	$ 50		$ 50		$ 50