Summary of Significant Accounting Policies - Summary of Revisions in Risk-Free Discount Rate Applied to Environmental Remediation Liabilities and Recovery Assets (Detail) (USD $)
In Millions, unless otherwise specified |
12 Months Ended | ||
---|---|---|---|
Dec. 31, 2014
|
Dec. 31, 2013
|
Dec. 31, 2012
|
|
Accounting Policies [Abstract] | |||
Charge (reduction) to Operating expenses | $ 10 | $ (13) | $ 3 |
Risk-free discount rate applied to environmental remediation liabilities and recovery assets | 2.00% | 3.00% | 1.75% |