Commitments and Contingencies - Environmental (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015 USD ($) sites	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) sites	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)
Loss Contingencies [Line Items]
Accrued obligations for environmental matters, current liabilities	$ 55		$ 55
Accrual for Environmental Loss Contingencies [Roll Forward]
Beginning balance	388	$ 416	404	$ 435
Accruals	0	8	3	13
Payments	(9)	(10)	(28)	(34)
Ending balance	$ 379	414	$ 379	$ 414
Environmental Issue
Loss Contingencies [Line Items]
Number of alleged environmental contamination sites (in sites) | sites	222		222
Number of environmental superfund sites (in sites) | sites	17		17
Liability for third-party tort claims	$ 12		$ 12		$ 15
Site Contingency, Estimated Time Frame for Accrued Cost Distributions			10 years
Future costs for environmental liabilities, minimum	295		$ 295
Future costs for environmental liabilities, maximum	510		$ 510
Environmental Issue
Loss Contingencies [Line Items]
Additional environmental expense	$ 7	$ 5